3D PLOTTER (aka. Technical Drawing) ---------- by Martin Clayton from ZX Computing, June/July 1984 Craft drawings can be viewed in several ways with this program from Martin Clayton of Knaresborough. When you have entered this program and first run it, a brief explanation of how it works is given. To get the most effective displays from it however, a few moments of preparation is necessary. The shape must be a prism although the cross section can have any number of points. Curves are not aliowed — even VU-3D, one of the best drawing programs on the market, has problems with curves. You must enter the coordinates of your shape as DATA in line 9000. These are relative co-ordinates as used in the DRAW statement and start at the bottom right corner to allow several views to be drawn on screen at once. A possible shape section is shown in the diagram and the co-ordinates are given. To use this in the program you would produce a DATA line as follows: 9000 DATA -50,0,-10,20,40,20,20,-40,1000 Note that 1000 is a "rogue" value to signal the end of the DATA to the computer. Once the required shape DATA has been entered, then the program can be RUN. After the title page you are asked to input the depth in pixels of the shape. The program then moves through four separate display modes. 1 ROTATIONAL The shape is moved through 90 degrees in a series of steps specified by yourself. 2 WORKING DRAWING Technically known as 1st Angle Orthographic Projection, the front, side and plan views are drawn in position. 3 OBLIQUE Where all the front facing planes are displayed in full and all the other horizontals are at 45 degrees. 4 ISOMETRIC All sides are displayed equally with all horizontals at 30 degrees. All the angles in this program are produced by a trigonometrical formula which was carefully and painstakingly worked out by Martin. At each stage of the display, an option to make a copy with the ZX printer is offered. The DATA included gives the shape that we have used for the screen prints. Try running the program with this to get an idea of the way the program works.