Return to CD Index

GemCad Reference Manual

The File Menu

The commands in this menu are to read and write disk files. GemCad deals with three types of files. There are a pair of commands to read and write each type.

Open (O) Open an existing project: read from a binary file

The Open (O) command is used to open an existing GemCad project file. Such a file is a binary file saved previously with the Save (s) or Save as (S) command. GemCad will prompt you for the name of the file. You may either type in the file name or just press the Enter key to use the file picker. If you type in the file name, the file must be in the current directory, or a full or relative path must be given (such as C:\CUTS\bril.gem or ..\QUARTZ\cut.gem). If there are already facets cut, GemCad will ask permission to trash them before asking you for the file name.

If you press the Enter key to use the file picker, GemCad will print a list of all of the files in the current directory whose extension begins with “G.” Subdirectories of the the current directory are also shown. The list of subdirectories follows the list of files. You can distinguish the two because directory names are followed by the \ backslash character. The directory ..\ is the parent of the current directory.

One of the selections will be in reverse video and will have a small arrow to its left. You may use the cursor keys or mouse to change which item is highlighted. You make a selection by pressing the Enter key or a mouse button. If you select a file name, GemCad will try to open the file. If you select a directory, GemCad will change to the new directory and display all of the files matching the wildcard and all of the subdirectories in the new directory. (A wildcard is a pattern that matches file names with certain characteristics.) There is also a special selection labeled file spec. This allows you to change disk drives or the wildcard. The default drive is the drive where you were when you started the program. The default wildcard *.G* matches any file name whose extension starts with G. The ? character matches any one character, and the * matches an arbitrary string of any length.

If you get into the file picker by accident, you can abort by pressing the Esc key or by selecting empty space. This leaves the previous design intact. If you select a directory, it becomes the new working directory.

The L&S import (M) command reads a project from a file compatible with the programs written by Robert Long and Norman Steele. Long and Steele have compiled a vast library of facet designs, and GemCad can import these files directly. These files are text files and and have names that typically end with the .P3D, .C3D, or .B3D extensions (for pavilion, crown, or both). GemCad will prompt you for the name of file. If you just press the Enter key, GemCad will bring up the file picker with the wildcard *.?3D. It will then scan the file and draw the stone on the screen. Next, GemCad will prompt you for the symmetry of the stone just as in the Symmetry (y) command.

GemCad will name each tier with a number in the same order as it appeared in the data file. GemCad will make the I.D. position of the index gear at the top of the screen. If the stone is longer than tall, you might have to scale it down with the Scale (X) to make it fit on the screen. GemCad will print an error message if it encounters a facet with less than three sides. Any error messages pertaining to the data file will begin with the line number in the data file at which the error was encountered.

Note:

The L&S import (M) command is mostly obsolete. The Datavue 2 database creates .ASC files that can be read in with the Read (R) command.

L&S export (E) Export project to a Long & Steele format file

The L&S export (E) command makes a disk file compatible with the programs written by Robert Long and Norman Steele. One of these is the RAYWIN program. GemCad will prompt you for the name of the data file. The name you enter should end with the .P3D, .C3D, or .B3D extension depending on whether your design is just a pavilion, just a crown, or both pavilion and crown, respectively. If you don't supply an extension, GemCad will add .B3D to the name.

There are several caveats to this translation process. The names of facets and the refractive index will be lost, and the cutting order will be changed to make the crown first in the data file. The orientation of the index gear will be changed to I.D. position at the top since that is the orientation that the Long & Steele programs expect, but the direction of indexing will be preserved. The z=0 plane will be made to coincide with the girdle line. This command might take a long time on machines without numeric co-processors.

Quit (Q) Quit GemCad

The Quit (Q) command is used to exit GemCad. You can also use the Esc key to quit. If you have not saved the current design since making a change or addition, GemCad will ask you if it is OK to quit anyway.

Help (h) Print out help for next command instead of doing next command

The Help (h) command shows up in every menu. The Help (h) command prints out a one- or two-line description of the next key that you press. The command corresponding to the key you press is not executed, however.

Print Screen (F12) Print what's on the screen

Function key F12 performs a screen dump. (If your keyboard does not have F12 or it doesn't work, you may use Shift-F2 instead.) This command shows up in every menu. This print screen function is completely independent of ordinary keyboard key labeled Print Scrn that invokes the DOS print screen function so it is not necessary to load the GRAPHICS.COM program for the F12 screen dump to work. GemCad supports IBM compatible dot-matrix printers and Hewlett-Packard LaserJet and DeskJet printers. See the configuration section of this manual to find out how to specify the printer type.

Crosshairs (Spacebar) The spacebar draws or erases the dotted crosshairs across the screen that intersect at the cursor.

The Crosshairs (Spacebar) command doesn't show up in any menu but is always available. The crosshairs are convenient for lining things up vertically or horizontally. It also serves to tack down the cursor if you use the mouse to pick items from the menu bar. If the command you plan to use requires a point, you can tack down the cursor with the spacebar. Then when you select the item from the menu bar, GemCad uses the location of the crosshairs and does not ask you to set a point.

Return to GemCad Manual Table of Contents

---

The Cut Facets Menu

The commands in this menu are for cutting new facets. The basic philosophy behind the cutting of new facets is that GemCad will cut a tier of facets as soon as you have given it enough information to specify one of the facets of a tier. (Facets on the same tier are cut at the same angle and depth and have indexes related to each other through the symmetry of the stone.) The section on the Symmetry (y) command gives more information on symmetry.

To determine the plane of a new facet, GemCad needs three pieces of information. There are several different combinations of three pieces of information that will determine the plane of a new facet:

One point, the index, and the angle

Two points and the index

Two points and an angle of 90°

Three points

The commands in this section allow you to give GemCad the angle or index of a facet to be cut. GemCad will cut the facet immediately after you give it the last piece of information needed to specify the facet. Sometimes you might not recall what information you have already specified. The status box in the lower-left-hand corner of the screen shows a summary of the information GemCad has for new facets. There are fields for the angle, index, and the number of points entered so far. If you have not given GemCad any information about a new facet, GemCad will display in the box the number of facets cut so far. To correct information in this field, the Draw (d) command will redraw the stone and clear this field and cause any pending information about new facets to be discarded.

Angle (a) Set the angle of a new facet

GemCad will prompt you at the top of the screen for the bearing angle (in degrees) of the new facet. Pressing the Enter key without entering an angle will abort the command. To correct an incorrectly entered angle, simply repeat the command and enter the correct angle. The new angle will replace the old.

Jam angle (A) Set the angle of a new facet to be the same as that of the facet surrounding the cursor

GemCad will search its database of facets and will find the facet surrounding the cursor. It will then duplicate the angle as if you had entered it with the Angle (a) command. This can be quite convenient when cutting step cuts with lot of facets cut at the same angle.

Index (i) Set the index of a new facet

GemCad will prompt you for the index. Indexes may be fractional. Pressing the Enter key without entering an index will abort the command. To correct an incorrectly entered angle, simply repeat the command and enter the correct index. See the Index gear (g) command to find out how to change the number of teeth on the index gear.

Jam index (j) Set the index of a new facet to be the same as that of the facet surrounding the cursor

GemCad will search its database of facets and will find the facet surrounding the cursor. It will then duplicate the index as if you had entered it with the Index (i) command. This can be quite convenient when cutting step cuts.

Change (C) Change the facet surrounding by the cursor: next new facet will replace it

The Change (C) command is used to recut a tier of facets. It is similar in action to killing a tier of facets with the Kill tier (K) command and then recutting the facet with two exceptions. First, the index of the old facet is rounded off to the nearest integer, and entered just as if you had entered it with the Index (i) command. (The index can then be changed to something else with the Index (i) command.) Second, after the new tier of facets is cut, the cutting order remains the same. (Killing a tier and cutting it again makes the new tier last in the cutting order.) The change command disables several other commands. The auto-backup feature is turned off until the facets are recut. Thus, the Undo (u) command will get you back to the point just before you executed the change command regardless of any other changes to the stone. Only one tier of facets may be changed at a time.

When a change is pending, an asterisk * will follow the index printed in the status box in the lower-left-hand corner of your display. If you discard the index with the Draw (d) command, GemCad will print the previous index in parentheses in the status box.

A problem can arise if you are cutting a design that has mixed symmetry, that is, some tiers of facets are cut with one type of symmetry and others are cut with another type of symmetry. GemCad does not keep track of which facets were cut with which symmetry setting. So, if you use the Change (C) command to change a tier of facets, make sure you set the symmetry properly for the changed tier.

Draw (d) Draw the stone again, discard set points

The Draw (d) command is used to redraw the stone. As you cut new facets, GemCad only redraws the facets that change. Sometimes in the process of redrawing, facet labels (see the Name (n) command) and index labels can become partially erased. Redrawing the stone cleans up the display. The Draw (d)g command also discards any pending information about facets to be cut (angle, index, or points) and clears the status box in the lower-left-hand corner of the screen. Thus, the Draw (d) command is also useful for correcting input errors.

The Draw (d) command also places dimension lines on the drawing of the stone. Each dimension is given by a single character L, W, P, C, or T corresponding to the length, width, pavilion, crown, and table. The relative values of these dimensions are listed with the List to scrn (l) or List to file (L) commands. If a facet is changed or a new facet is cut that changes the dimensions of the outline or table, the dimension lines will not be updated on the screen until the Draw (d) command is executed.

Zoom (z) Zoom in on the view surrounding the cursor or zoom back out again

The Zoom (z) command enlarges the view containing the cursor to fill the entire screen. The zoom command toggles between two magnifications--the command doesn't do arbitrary magnifications. If one view fills the screen, the zoom command will zoom back out to the four views.

Undo (u) Undo the last command that changed the stone

The Undo (u) command undoes the most recent change to the stone. Before each change to the stone, GemCad saves the stone to disk in a file called gemcad.bak in the current directory. The undo command simply reads in this file. Undo only undoes the previous command--repeated undos have no effect. If you are running the program off a diskette, it must not be write-protected. If you exit GemCad without saving the changes with the Save (s) command, if (forbid!) the program crashes, you have a power failure, or if your toddler pushes the red button on your tower system, you can get back to one step before the disaster by restarting the program and pressing the Undo (u) key as the first command.

Return to GemCad Manual Table of Contents

---

The Point Menu

The following commands are used to set points that will be used to cut a new tier of facets. Whenever you enter one of the point commands, GemCad will draw cross-hairs intersecting at the point you specified. (If the command picks a point relating to facets already cut, there might be a slight delay while GemCad does the search.) GemCad will then print the coordinates of the point and ask you if you want to use the point (as a piece of information for the cutting of a new tier of facets) or discard it. Any answer beginning with y will be taken as yes, and anything else (including just the Enter key) will be taken as a no. If you are using a mouse, the left button is equivalent to a y, and the right button is equivalent to the Enter key. Thus, pressing the left and then the right buttons is equivalent to a yes response, and pressing just the right button is equivalent to a no response. The number of points set so far is displayed in the box in the lower-left-hand corner of the screen. The following section describes each point command in detail.

Meet pt (m) Set a point of a new facet at the existing meet point nearest cursor

GemCad will search its database of vertexes (meet points of three or more facets) and find the one nearest the cursor in the “Manhattan sense” (sum of vertical and horizontal distances). The cursor will “snap” to the meet point and GemCad will ask you if you want to use the point. Since the exact meet point is determined by the equations for the planes of the facet, the point is set to much finer precision than the resolution of the display you are using. When the cursor is visible, the left mouse button is equivalent to the Meet pt (m) command.

Pt on edge (e) Set a point of a new facet on the edge of an old facet nearest cursor

GemCad will search its database of edges of facets (the intersections of two facets) and find the one nearest the cursor in a vertical or horizontal direction. The cursor will snap vertically or horizontally on the screen to the nearest edge, and GemCad will print the x-y-z coordinates of the point and ask you if you want to use the point. Only one of the x-y-z coordinates depends on the screen resolution; the other two depend on the equations of the two facets that form the edge. When the cursor is visible, the right mouse button is equivalent to the Pt on edge (e) command.

Pt on facet (f) Set a point of a new facet on the interior of an old facet at cursor

GemCad will search its database of facets and determine which facet surrounds the cursor. GemCad will then project the line of sight through the cursor and calculate the point of intersection of this line and the facet. GemCad will print the x-y-z coordinates of the point and ask you if you want to use the point. Since GemCad determines two of the three coordinates from the cursor position, the resolution of this command is limited to that of your particular display. Even with CGA resolution, however, this is seldom a serious limitation unless cutting designs with small “floating” facets. When the cursor is visible, the center button on a three-button mouse or pressing both buttons of a two-button mouse are equivalent to the Pt on facet (f) command.

Z-axis incpt (Z) Set a point where the plane of the facet surrounding the cursor intersects the z (dop) axis.}

This command is useful if you are cutting several facets to a common centerpoint. It's also an easy way to cut two facets at the same angle and mast height. Place the cursor inside an existing facet. If the facet encloses the centerpoint of the Top View, GemCad will pick this point of intersection. Otherwise, GemCad will project the plane of the facet and compute the point of intersection with the z (dop) axis. GemCad will ask you if you want to use the point.

Pierce zero (p) Set a point of a new facet where the cursor pierces the zero plane

This is the probably the most difficult of the point commands to understand, but it is seldomly used. Each of the four views shows a projection of the stone onto one of the three coordinate planes. The Top View is the projection of the stone onto the x-y plane. (The z axis is the axis of rotation of the dop.) In the Top View, the p command will set the x and y coordinates to those of the cursor, and the z coordinate will be set to zero. In the End View, the Pierce zero (p) command sets the x and z coordinates, and the y coordinate is zeroed. In the Side View, the Pierce zero (p) command sets the y and z coordinates, and the x coordinate is zeroed. As with the other point commands, GemCad will draw cross-hairs, print the x-y-z coordinates of the point and ask you if you want to use the point.

The Pierce zero (p) command is useful for making a preform from a sketch. One method is to sketch or photocopy a sketch of the stone on a transparency and tape it to your screen. Zoom in on the Top View (with the Zoom (z) command) and center the dop axis on the dot at the center of the Top View. The sketch should have the girdle outline divided into line segments. Enter an angle of 90 degrees and set two consecutive points on the girdle outline with the Pierce zero (p) command. GemCad will cut the resulting facet. If you go all the way around the girdle outline in this fashion, you will cut a preform of girdle facets at 90° with the same outline as your drawing.

The indexes of the resulting facets will not be whole numbers, however. You can use the Change (C) command to change the index of each facet to a whole number. You then cut facets around the stone to a temporary center point, working in the Side and End Views. These facets must be at the same indexes as the girdle outline facets to make a level girdle. (You can use the Jam index (j) command to duplicate the index of the facet surrounding the cursor.) This makes what is commonly referred to as a C.A.M. (Centerpoint Angle Method) Preform.

Query user (q) Query user for x, y, and z coordinates of a point of a new facet

If you know the (x, y, z) coordinates of a point on a new facet, the Query user (q) command allows you to enter the numeric values of the coordinates directly from the keyboard. GemCad will prompt you for each of the three values in turn. When cutting a C.A.M. preform, it's sometimes best to start with the point (0, 0, 1).

Bysect (y) Set a new point a fraction of the way between the previous two points.

The Bysect (y) command sets a point along the line segment joining the previous two points. GemCad will prompt you for the fraction of the distance. A value of zero will select the first point, and a value of one will select the second point. A value of 0.2 will select a point 1/5 of the way from the first to the second point (nearer the first point). Typically, the two points are selected with the Meet pt (m) command. When GemCad asks you whether to use the points, you will usually want to enter n to not use the points to cut a new facet. If you instead enter y to use the two points, and then use the Bysect (y) command to enter a third one between these two points, GemCad will likely complain about the points being co-linear.

Tack (t) Tack down next point to align horizontally or vertically with the previous point.

The most common use of the Tack (t) command is to force a new edge be exactly horizontal or vertical in one view. Without the tack command, the resolution of the display limits how close you can get to a horizontal or vertical line since the cursor can only move by one pixel at a time. GemCad will choose the vertical or horizontal alignment from the relationship of the cursor to the previous point. If the horizontal distance from the cursor to the previous point is greater than the verticl distance, GemCad will align the new point horizontally. The previous point can be from any of the point commands, but most often it is the Meet (m) command.

The Tack (t) command doesn't set a point directly, but forces the next point to align with the previous one. The previous point is usually a Meet (m) point but doesn't have to be. The previous point used by the Tack (t) command doesn't have to have been used for a new facet. The sequence most often used is Meet (m), answer y to use the point, Tack (t), Pt on Facet (f), and answer y to use the point. An index with the Index (i) command is often given next to provide the third piece of information to specify the facet.

For convenience, the Draw (d), Zoom (z), and Undo (u) commands are also found in the Point Menu. They are described above in the section on the Cut Facets Menu.

Return to GemCad Manual Table of Contents

---

The Edit Menu

Most of the commands in the Cut Menu change the stone in some way.

Xfer (x)Transfer the stone

The Xfer (x) command is used to transfer the stone. The stone will be turned upside-down. What was in the Top View will be in the Bottom View. You will find it easiest to do most cutting in the Top View. This is because the Top View aligns horizontally with the Side View and vertically with the End View.

Kill facet (k) Kill the facet surrounding the cursor

The Kill facet (k) command deletes a single facet. The facet is erased and the facets it used to share an edge with are recomputed and redrawn. This can be a slow process on machines without numeric co-processors.

Kill tier (K) Kill a tier of facets, one of which surrounds cursor

The Kill tier (K) command kills an entire tier of facets. The facets are erased, and each facet that shares an edge with one of the killed facets is recomputed and redrawn. This command can be quite slow on machines without numeric co-processors.

Center (c) Center the current view about the cursor

The Center (c) command is used to center the stone about the cursor in the view containing the cursor. Let's consider the End View. The End View shows a projection of the stone in the x-z plane, with x increasing to the right and z increasing up the screen. Let's say that your stone positioned too far up in the End View and you want to move it down. Move the cursor inside the stone to its approximate center by eye and press the Center (c) key. (Only the vertical position of the cursor is important.) The cursor should be above the dot at the center of the End View. GemCad will ask which coordinate you want centered. Enter z. GemCad will redraw the stone, sliding the stone down so that the position you specified is at the center of the End View. GemCad will slide the stone down the vertical distance from the cursor to the center dot.

The center command can also be used to shift the center of the dop axis by centering the x or y coordinate in the Top or Bottom Views. This is useful for pears and other stones with 1-fold symmetry. This will force the stone to be retiered since facets that used to be at the same mast height will no longer be after offsetting the center. With some deleting and recutting, this can be used to create the start of a marquise from a portion of a round design.

You will get an error message if the coordinate you specify has its axis perpendicular to the view containing the cursor, or if the stone is already centered about the cursor. For instance, if you tell GemCad to center in the z direction while the cursor is in the Top View, GemCad will tell you that you are in the wrong view to center that coordinate since the z axis is perpendicular to the Top View.

When GemCad cuts a facet it conceptually cuts the stone in two at the plane of the facet and discards one part of the stone and keeps the other. How does GemCad know which part to keep and which part to discard? The rule is that GemCad keeps the part of the stone containing the point (0, 0, 0) and discards the other part. The (0, 0, 0) point is marked by a dot at the center of each view. If you are cutting a skinny stone such as a marquise and you are having problems with GemCad cutting a facet in the wrong place, cutting away most of your stone, GemCad could be cutting off the part you really want it to keep. The solution to this problem is to use the center command to slide it up or down so that the center dot is contained in the part you want GemCad to keep.

Rotate/Tilt (r) Rotate/tilt the stone; will prompt for what fraction of a revolution

The Rotate/Tilt (r) command will rotate the stone clockwise in the view containing the cursor. Thus, if the cursor is in the Side or End View, the stone will be tilted. If the cursor is in the Top or Bottom View, the stone will be rotated about the axis of the dop. GemCad will prompt you for the numerator and denominator of the fraction of a revolution you want to rotate or tilt the stone. Thus, if you want to rotate the stone, say, 10 degrees, enter 10 for the numerator and 360 for the denominator. To rotate the stone one-half revolution, enter 1 for the numerator and 2 for the denominator.

Tan ratio (T) Tangent ratio scale top or bottom keying off of facet surrounding cursor

The Tan ratio (T) command is used to change all of the angles of one side of the stone to adapt a design to a different index of refraction. GemCad will search its database of facets to find the facet surrounding the cursor. The angle of the facet will be printed and GemCad will prompt you for the new angle of this facet. The entire side of the stone containing the selected facet will be scaled by the ratio of the tangents of the two angles. If the stone does not have a level girdle, the junction of the pavilion and crown might be distorted. If this is the case, the Playback (P) command can be used to recompute all facet edges and make the facets meet properly.

Waytwace (w) Trace a light ray from cursor into stone and back out of stone

The Waytwace (w) command twaces a single way--ahem!--traces a single ray of light through the stone. This is the only command in the Cut Menu that does not change the stone. It was placed in the Cut Menu to be close to the Tan ratio (T) command. The light ray will enter the screen perpendicular to the cursor, bounce around in the stone and then exit the stone. The ray is shown in all four views. This is a single-shot sort of a deal--one ray of light per command. A separate program (see the READ.ME file on your GemCad distribution diskette) is used to make ray-traced images of your design. You can note the leaky spots in the design and use the Waytwace (w) command to find out the cause of the leak. The Refr index (I) command is used to change the index of refraction. Rays are drawn in complement mode--shooting an identical ray a second time will erase it. A good ray should enter and exit crown facets.

Scale (X) Scale the stone: change angles, shrink, enlarge, stretch, etc.

The Scale (X) command is used to stretch or shrink the stone in one direction. The command has several variations. GemCad will ask you

Code (all, top, bot, x, y, z)?

The scale command has several uses. If your response begins with an a or A, GemCad will scale the entire stone. GemCad will prompt you for the numerator and denominator of the factor by which the stone is to be multiplied. The stone is enlarged if the numerator is larger than the denominator or shrunk if the denominator is larger than the numerator. No angles or indexes are changed.

A response beginning with x or X will stretch or shrink the stone horizontally in the Top View. You can use this, for instance, to turn a round design into an elliptical one. A response beginning with y or Y will stretch the stone vertically in the Top View. In either case, GemCad will prompt you for the numerator and denominator of the scale factor. Angles and indexes will be changed. Indexes will probably not be whole numbers; the Change (C) command may be used on each tier to make its index a whole number. Facets that used to be at the same index and depth before the scale command might be at different angles and depths after scaling.

When you scale the stone with the Scale (X) command in the x or y directions there is no guarantee that the indexes will be whole numbers. This happens when you stretch a round design into an oval, for instance. After scaling the stone GemCad will ask you if you want it to try to round off the indexes to the nearest notches. If you answer yes, GemCad will search through the following index gears: 64, 72, 80, 96, and 120. It will sort them in order from best to worst. The “best” gear is the one that makes the indexes come out to be nearest to whole numbers (nearest in angle, that is). GemCad will then ask you for the index gear. If you just press Enter, GemCad will use the first gear in the list. If you want a different gear (even if it is not in the list) just type it in here. It will then proceed to try to round off the indexes.

The algorithm GemCad uses is an iterative one. It will redraw the stone several times. You will see the meet points move and the facets change shape as GemCad tries to round off the indexes. After this process, you might have to use the Change (C) command to make the facets meet up again, particularly with the gears with fewer numbers of teeth. If you don't have a math coprocessor, this process will be very slow! You can press the Esc key to interrupt the process if it is taking too long or changing the shape too much. The iterative process will occasionally diverge on narrow stones or stones that have facets too close together in index. If this happens, it will print an error message and then undo the scaling. The smaller the number of teeth on the gear and the closer in index the facets are, the more trouble GemCad will have. The L/W ratio might be slightly different than what you asked for.

After the nearest-notches process, GemCad will retier the stone and automaticlly figure out the new symmetry. The retier operation groups together facets cut at the same bearing angle and depth regardless of their relationship through symmetry. To force the retier operation without otherwise changing the stone, scale the stone in the x (or y) direction by a factor of 1 over 1. After the stone is retiered, GemCad checks the design and resets the symmetry to 1, 1-y, or 2-y, whichever is appropriate. (See the Symmetry (y) command.)

If your response begins with a t or T, GemCad will scale the side of the stone currently in the Top View, be it the pavilion or crown. If your answer begins with a b or B, GemCad will scale the side of the stone in the Bottom View. A response beginning with z or Z will stretch or shrink the stone vertically in the End View thus scaling both the pavilion and crown by the same factor. All three variations perform Tangent Ratio scaling. In most cases, however, the Tan ratio (T) command is easier to use. GemCad will prompt you for an old angle and a new angle. GemCad will scale the stone such that a facet which was formerly at the old angle will be at the new angle. This will change the angles but not the indexes. If your stone does not have a level girdle, the girdle line might be distorted somewhat after the stone is scaled. This can be fixed with the Playback (P) command.

The Undo (u) command is also duplicated in the Cut Menu. It is described in the section on the Cut Facets Menu above.

Return to GemCad Manual Table of Contents

---

The Parameter Menu

The commands in the Parameter Menu are used to set parameters or switches.

Index gear (g) Change the index gear

The Index gear (g) command is used to change the number of teeth of the index gear. GemCad defaults to a 64 tooth gear when first run. After you press the Index gear (g) key, GemCad will prompt you to enter the number of teeth on the index gear. GemCad has provision for clockwise and counter-clockwise orientations. Gears with positive numbers of teeth increase counter-clockwise, and gears with negative numbers of teeth increase clockwise. Next GemCad will ask you for the offset. This is the index which will appear at the bottom of the circle of numbers in the Top View. An offset of zero causes the I.D. position to be at the bottom, and an offset of half the number of teeth of the gear cause the I.D. position to appear at the top. Pressing Enter without entering an offset also makes the I.D. position to appear at the bottom. The number of teeth must be a whole number, but the offset may be fractional.

Symmetry (y) Change the degree of radial symmetry and whether mirror-image symmetry

The Symmetry (y) command allows you to tell GemCad how many facets make up a tier and are cut at the same angle and cutting depth (mast height). GemCad will prompt you for the degree of radial symmetry and whether or not the stone has mirror-image symmetry. The stone and index gear will then be redrawn.

The degree of radial symmetry is the minimum number of facets which will be cut at once. Facets at an angle of zero are the only exception to this rule since they can be cut at any index. If the stone has mirror-image symmetry, twice as many facets as the degree of radial symmetry can be cut at once. The exceptions are facets that are mirrored by themselves--facets whose indexes are integer multiples of the number of teeth on the gear divided by twice the degree of radial symmetry. Consider an example. A standard round brilliant has eight-fold radial and mirror-image symmetry. If enough information is given to cut one of the break facets, GemCad will cut all sixteen break facets at once. It knows, however, to cut only eight mains and stars because these facets are mirrored by themselves.

What about other symmetries? If the stone is put at the center of a pie, the degree of radial symmetry is the maximum number of identical wedge-shaped pieces into which the stone can be cut. If it can't be cut into at least two pieces, the degree of radial symmetry is one. If each of the identical pieces has bilateral symmetry (if it can be folded in two along its centerline) then the stone also has mirror-image symmetry. Consider some examples. A snowflake has six-fold, mirror-image symmetry. It can be cut into six identical pieces, and each of the six pieces can be folded in two. A pear-shaped stone has no radial symmetry, but has mirror-image symmetry so it has one-fold, mirror-image symmetry. A stone whose outline is a parallelogram has two-fold radial symmetry but does not have mirror-image symmetry. An emerald cut has two-fold, mirror-image symmetry. Most triangular stones have three-fold, mirror-image symmetry.

Eight-fold, mirror-image is the default when GemCad is first run. The default can be changed when configuring GemCad. The symmetry of the stone is saved when the project is saved with the Save (s) or Save as (S) commands. You can change the symmetry in the middle of a design. For instance, you can cut a pavilion with one type of symmetry and a crown with another. Only the current symmetry is listed by the List to scrn (l) or List to file (L) commands.

If the number of teeth on the index gear is not an integer multiple of the degree of radial symmetry, GemCad will round off indexes to the nearest tooth. This allows you, for instance, to cut a seven-sided stone on a 64 index gear.

Refr index (I) Index of refraction: change it and print the critical angle

The Refr index (I) command is used to change the index of refraction for the Waytwace (w) command. GemCad will tell you the old index of refraction and will prompt you for the new one. GemCad will then print out the critical angle in the upper-left-hand corner of the display. A null response (just the Enter key) causes the R.I. to remain unchanged, but the critical angle is displayed again. When you save a design GemCad saves the R.I. with the facet data. When GemCad is first run, the refractive index is set to 1.54 for quartz. This default can be changed when you configure GemCad.

Return to GemCad Manual Table of Contents

---

The Utility Menu

Blink facet (b) Recompute the facet surrounding the cursor

The Blink facet (b) command erases the facet surrounding the facet, recomputes it, and then redraws (blinks) it. This is the quickest way to find out the angle and index of a facet: they are printed in a box at the upper-left-hand corner of the screen.

Blink tier (B) Recompute a tier of facets, one of which surrounds cursor

The Blink tier (B) command recomputes an entire tier of facets. GemCad searches its database of facets and finds the one surrounding the cursor. All facets belonging to the same tier as the specified facet are recomputed and redrawn (blinked).

Meas vector (v) Display distance, angle and index of line joining last two points

A vector is a quantity with magnitude and direction. The Meas vector (v) command is used as a measuring stick. It gives the length and direction of the line joining two points. To use the Meas vector (v) command, pick two points, typically with the Meet pt (m) command (or the left mouse button). When GemCad asks you to use the points, enter “n” or just press Enter. Then press the Meas vector (v) key. GemCad will print the distance between the two points projected along each axis and also give the true length of the line joining the two points. Next, GemCad will print the bearing angle and index of the line joining the two points. One use for this feature is to figure out the minimum angle needed to cut off an edge.

Set vector (V) Set units for Meas vector (v) command

The Set vector (V) command is used to set the length of the measuring stick used for the Meas vector (v) command. The main use of this feature is to allow you to measure the ratio of two lengths without having to divide the numbers yourself. Let's say you want to measure the length of a feature on a design as a fraction of the width of the design. First, pick two points on opposite sides of the stone with the Meet pt (m) key. (But tell GemCad not to use the points for a new facet.) Next, press the Set vector (V) key. GemCad will print the length and direction of the line joining the points as in the Meas vector (v) command. GemCad will then ask you along which axis you want the distance to be set and how many units long you want this segment to be. For instance, if you want your measuring stick set such that the width of the stone is one unit and your stone is longer than it is wide, pick two points opposite one another at the widest point of the stone. Press the Set vector (V) key. Press Enter twice to acknowledge the length and direction in the old units. GemCad will then ask you along which axis the length is measured that to you wish to set. Next it asks how many new units long to set this distance. In most cases, you will probably want to set this distance as one unit long.

Playback (P) Recut the stone

The Playback (P) command is used to recut the stone. The stone is shown at every stage as it is recut. GemCad will ask you if you want it to wait for you to press a key between facets. If your answer begins with a “y” GemCad will cut facets one at a time, waiting for you to press any key or mouse button. Otherwise, GemCad will ask you how long to wait between facets. A value of 0.5 seconds slows things down enough to see each facet as it is cut. The default is not to wait at all. Since the playback can take a long time on machines without numeric co-processors, pressing the Esc key will abort the playback. The overall effect of the playback is to show an animation of the stone as it is cut. The playback command also recomputes the stone and can sometimes improve the appearance of meet points or edges. You should use the Playback (P) command after the Tan ratio (T) command to improve the accuracy of the computed meet points.

Demo (D) Recut the stone repeatedly to demonstrate GemCad

The Demo (D) command repeatedly executes the Playback (P) command in an endless loop. As with the Playback (P) command GemCad will ask you how long to pause between facets. After the stone is recut, GemCad will pause for five seconds. The demo will continue until you interrupt it with the Esc key.

Constr line (-) First time starts at cursor, second time draws to cursor

The first time you press the Constr line (-) key, GemCad does nothing except to save the last location of the dotted cross-hairs (or the cursor if the cross-hairs are not on). The second time you press the minus key, GemCad will draw a dotted construction line from the saved point to the new location of the crosshairs (or cursor). You can get crosshairs at the cursor by pressing the space bar.

Dos (!) Execute a DOS command

The Dos (!) command allows you to executes one or more DOS commands. GemCad will prompt you with DOS> at the top of the screen, and you may enter a one-line DOS command which will be executed in a text screen. After DOS executes the command, GemCad will ask you to press any key to redraw the stone.

If you want to escape to a DOS session to execute several commands and then return to GemCad, simply press the Enterg at GemCad's DOS> prompt. This will start new DOS session in a text screen. When you finish the DOS session, you must use the EXIT command of DOS to return to GemCad.

Return to GemCad Manual Table of Contents

---

The Diagram Menu

List to scrn (l) List cutting schedule of angles and indexes to screen

The List to scrn (l) command lists the cutting schedule to the screen. Facets are listed in the order they were cut. GemCad will wait for you to press any key or mouse button at the bottom of each full screen of text. If you have used the Heading (H) command to enter the design name and author, the listing will begin with the heading. The relative length, width, table length, and pavilion and crown heights are shown next. These dimensions are those called out on the diagram. The facets visible in the Top View are labeled “Crown,” and those in the Bottom View are called “Pavilion.”

Each tier of facets is given by one or more lines in the listing. The tier begins with its name (see the Name (n) command) if it has one. Next comes the bearing angle in degrees. Next come the list of index positions separated by hyphens. This might take several lines. The rightmost column contains the cutting instructions if you have entered them with the Gloss (inst) (G) command.

If you have used the Footnote (F) command to enter a footnote, the note will be at the bottom of the listing.

List to file (L) List cutting schedule of angles and indexes to printer or file

The List to file (L) command lists the cutting schedule to a file or printer. The format is basically the same as with the List to scrn (l) command. GemCad will prompt you for the name of the file, which must be a valid DOS file name. If the file exists, GemCad will ask for your permission to write over the file. Entering the file name PRN, or a port name such as LPT1 or COM1, whichever is appropriate on your system, will list the cutting schedule to the printer. The file that is written is a flat ASCII text file. You may use your favorite text editor or word processor to annotate the cutting instructions and print them out.

The format of the List to file (L) command is somewhat different than that of the List to scrn (l) command. The heading and dimensions are set off in an indented block by themselves. The cutting instructions follow. When you configure GemCad, you can specify the margins, the height of the header and how much the header is indented.

The volume of the stone is shown with the List to scrn (l) and List to file (L) commands. The volume is displayed as a fraction of the cube of the width, Wł, of the stone. For example,

Vol./W^3 = 0.279

This notation means that the volume of the stone divided by the cube of the width of the stone is equal to 0.279. The cube of a number is the number multiplied by itself three times. The volume fraction can be used to estimate the carat yield of a finished cut. The width W of the stone is shown on the screen and is measured either horizontally or vertically in the top view, whichever is smaller. To use the volume fraction to estimate carat weight, measure W with a caliper in centimeters (mm/10), compute W cubed (W times W times W), and multiply the result by the specific gravity of the material in g/cc times the number for volume fraction Vol/W^3 given by GemCad. The result will be the estimated weight of the stone in grams. Multiply by 5 to get the weight in carats.

As an exercise, let's compute the weight of a 12 mm wide stone of quartz with Vol./W^3 = 0.279. Noting that quartz has a specific gravity of 2.65 g/cc, and 12mm = 1.2cm,

Weight = 1.2 x 1.2 x 1.2 x 2.65 x 0.279 = 1.28 grams x 5 = 6.39 carats

If you prefer, you can use mm instead of cm, but the weight will come out in milligrams. You then divide by 200 to get carats. For our example,

Weight = 12 x 12 x 12 x 2.65 x 0.279 = 1280 mg / 200 = 6.39 carats

Note that the volume fraction depends on the actual girdle thickness shown in the diagram, so it will vary with the girdle thickness shown on the screen.

Name (n) Name or label the facet surrounding the cursor

The Name (n) command searches the database of facets to find the facet surrounding the cursor. GemCad then prompts you for the name of the facet and labels the facet with the name. Names can be up to three characters, although only one or two character names will fit in any but the largest facets. The names will also appear in the cutting schedule (made by the List to scrn (l) and List to file (L) commands). Naming a facet that already has a name renames the facet, but a null name (just the Enter key) will erase the name. If two facets in the same tier of facets (same angle and depth) are named different names, only one name will appear in the cutting schedule.

Gloss (inst) (G) Provide cutting instructions for facet surrounding the cursor

A gloss is a brief explanation or annotation. The Gloss (inst) (G) command allows you to provide brief cutting instructions for a tier of facets, one of which surrounds the cursor. The cutting instructions will be printed on the listing made with the List to scrn (l) or List to file (L) commands to the right of the indexes that make up the tier.

Heading (H) Enter a heading including title, designer, date, etc.

The Heading (H) command allows you to enter up to four lines of text that show up at the top of the listing with the List to scrn (l) or List to file (L) commands. If you have already used the Heading (H) command to enter a heading, subsequent times allow you to edit the heading. You may use the Insert, Delete, End, and Home keys. The purpose of this text is to allow you to enter the name of the design, the designer, the date and reference.

Footnote (F) Enter a footnote

The Footnote (F) command allows you to enter up to four lines of text that are printed at the bottom of the listing made with the List to scrn (l) or List to file (L) commands. If you have already used the Footnote (F) command to enter a footnote, subsequent times allow you to edit the footnote. You may use the Insert, Delete, End, and Home keys.

Return to GemCad Manual Table of Contents

---

Configuring GemCad

When you first run GemCad it will print out a Copyright notice, tell you where it got its current configuration, and ask you press c to configure or any other key to start the program. If you press the c or C key, GemCad will enter its configuration mode. This allows you to change the default parameters such as index gear and symmetry. It also allows you to specify parameters relating to your printer. This configuration is stored in a file named GEMCAD.CFG in the current working directory.

When GemCad is first run, it tries first to find a file called GEMCAD.CFG in the current working directory. If it cannot find such a file, it looks in the same directory in which the GEMCAD.EXE resides for a file named GEMCAD.CFG. If it can't find either configuration file, it just uses the defaults built into GEMCAD.EXE. You can therefore make a generic configuration in the same directory where GemCad resides and then make different directories for special situations.

The questions about margins and headers pertain to the format of the listing produced with the List to file (L) command. The List to file (L) command is set up to make a listing that can be printed with the diagram produced with the GemPlot, GemJet, or GemDot programs. These programs produce publication-quality diagrams on various printers from your GemCad files. They do not print the cutting instructions, however. Since the margins, character pitch and line spacing vary with the type of printer, GemCad allows you to adjust the print position of various parts of the diagram.

The first part of the listing is the header. It contains the heading as entered with the Heading (H) command, a tally of the number of facets, some parameters, and the dimensions of the stone. The header is indented more than the cutting instructions that follow. Blank lines follow the header so that the cutting instructions always begin on the distance from the top of the page regardless of the length of the header.

The four parameters that you can set are:

Top margin: The number of blank lines from the top of the listing to the first line of the header.

Left margin: The number of spaces before each line of the cutting instructions.

Top header: The maximum number of lines in the header, or the number of lines from the top margin to the beginning of the cutting instructions.

Left header: The extra number of spaces that the header is indented.

If you set these four parameters to zero, the format of the List to file (L) command will be identical to the format of the List to scrn (l) command.

The default choices for these were tested with the GemDot prorgram with Epson LQ510 printer using its Courier typeface. You will have to experiment with the margins to adapt the listing format to your printer.

GemCad can print a copy of the screen on HP DeskJet, LaserJet, or IBM or Epson printers. All of the HP printers need the information in one format and the IBM and Epson printers need it in another. If you select the IBM compatible printer, GemCad will ask you for the aspect ratio of your printer. For most 9-pin printers, enter 1.2. For most 24-pin printers, enter 1. GemCad will print only the square plotting area of the screen. Make a test plot with one of the suggested values above and measure the square to make sure its width is the same as its height. If not, reconfigure GemCad and multiply the aspect ratio by the ratio of the width to the height. If you select the HP compatible printer, the aspect ratio is ignored since all of the HP printers have square pixels.

Return to GemCad Manual Table of Contents

---

Error Recovery

What if you press a key that executes a command that you didn't intend to? Let's say you pressed the Angle (a) key by mistake. GemCad will ask you to enter the angle. If you just press the Enter key or the right mouse button, GemCad will abort the command.

What if you enter an angle incorrectly and don't realize it until after you have pressed the Enter key? Just press the Angle (a) key again, this time entering the angle correctly.

What if you enter an angle when you meant to enter an index? If you redraw the screen with the Draw (d) key, GemCad will discard all data pertaining to new facets and will clear the status box in the lower-left-hand corner of the screen.

What if you accidently gave GemCad enough information to cut a facet that you really didn't want to cut? You can wait until GemCad finishes and then use the Undo (u) key. What if you tell GemCad to cut a facet that starts hacking away at your stone? If a facet is cut off, GemCad will tell you so in an error message telling how may facets were cut off. You must then press any key to acknowledge the error message. You may then use the Undo (u) key to uncut the facet. If GemCad seems to be taking a long time to compute the new facets, you may interrupt it by pressing the Escape key. This immediately does an undo. The Escape key will also interrupt the Kill facet (k) or Kill tier (K) key commands.

If a new facet misses the stone entirely, GemCad will sometimes draw a “stone within a stone.” The way out of this is with the Undo (u) key. What if you've already changed the stone so that the undo key doesn't get rid of the “phantom” facets? You can position the cursor inside the phantom facet, press the Blink facet (b) key and make sure only the phantom facet blinks, and then kill the facet (or tier) with the Kill facet (k) or Kill tier (K) keys. It might be necessary to move to a different view or to rotate the stone with the Rotate/Tilt (r) key to specify the phantom facet unambiguously. Again, before using the Kill facet (k) or Kill tier (K) keys to kill a phantom facet, check first with the Blink facet (b) key to make sure GemCad will kill the facet you want it to kill.

Last resort: If things are totally hopeless, if your two-year-old has pressed the red reset button, or if there has been a power failure, there is still hope. Restart your computer, change directories to where you were when you last ran GemCad, run GemCad and execute the Undo (u) key. This will read in the file GEMCAD.BAK and get you back to one step before the catastrophe. It is important to do this before reading in any other file or cutting any new facets since any command that changes the stone will overwrite the file.

Return to GemCad Manual Table of Contents

---

Using GemCad with a Mouse

Versions 2.0 and later of GemCad support a Microsoft or compatible mouse (most are). If GemCad doesn't recognize your mouse, the problem is probably the mouse driver software. On some systems you must load the mouse driver MOUSE.COM before running GemCad. This is most commonly done in the AUTOEXEC.BAT file, but may be done anytime at the DOS prompt. (GemCad does not work with device-drivers such as MOUSE.SYS that are loaded in the CONFIG.SYS file.)

You can use the mouse to position the cursor and to execute commands. If you move the mouse pointer into the menu label area at the left of the screen, you can highlight a particular menu choice. Pressing any of the mouse buttons while a choice is highlighted will select that choice. This is equivalent to pressing the corresponding function key with one exception: if the command you selected refers to a point, GemCad will print “Set a point” in the upper-left-hand corner of the screen. The selected menu choice will then remain lit until you move the cursor into the drawing area, position the cursor at the point you want and then press a mouse button. The command will then be executed just as if you had pressed the corresponding function key while the cursor was at the point you set.

When the cursor is positioned in the drawing area and a menu choice is not highlighted, the mouse buttons are mapped to commands in the Point Menu. The left button is mapped to the Meet pt (m) command, and the right button is mapped to the Pt on edge (e) command. If you have a three-button mouse, the center button is mapped to the f (point on facet) command. (On a two-button mouse, pressing both buttons simultaneously will also perform the Pt on facet (f) command.)

When GemCad is prompting you for input at the top of the screen, the left mouse button is mapped to the y key and the right button is mapped to the Enter key. Thus, to answer yes to a yes or no question, press the left and then right mouse buttons. To answer no, enter a null response by pressing just the right mouse button. The center button (if present) is mapped to a backspace.

Consider an example. To set a meet point and use it to add a new facet, move the mouse near the meet point, press the left button (mapped to the Meet pt (m) command). GemCad will then ask you if you want to use the point. Press the left button (mapped to y) and then the right button (mapped to Enter). You can set meet points, points on edges, and points on facets without touching the keyboard.

The cursor keys work exactly the same way with a mouse as they do without. They are convenient for moving the cursor vertically or horizontally from another point on the screen.

There are two environment variables that pertain to the mouse when used with GemCad. If you mouse seems to move two or more pixels in one axis or if the cursor keys don't seem to work in one of the four directions, read further. If you type “SET MXDIV=2” at the DOS prompt prior to running GemCad, the program will divide the X mouse ticks by two. This makes the mouse half as sensitive horizontally as before. Similarly the variable MYDIV divides the vertical mouse ticks. You can put one or both of these commands in your AUTOEXEC.BAT file. If you get a DOS error message like “Out of environment space,” you must place the SET commands near the top of your AUTOEXEC.BAT file. Most of the newer mouse drivers have adjustable resolution, and you should fix the problem there.

Return to GemCad Manual Table of Contents

Return to CD Index