Conversion to PostScript

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# Conversion to PostScript

To visualize the structure as in reconstruction we modified software originally written by Geri Wagner. This program was written for Hewlett Packard work stations. As input the program takes a file with x-, y, and z- coordinates of points. The output is a PostScript program. When sent to a PostScript printer, the output of this program is a projection of the three-dimensional points down in two-dimensions. At each point, a small box is printed. Because only three sides of a box can be seen at the time, only these three sides are printed. The PostScript programming language is suitable for visualization tasks like these. The principle used here is that the boxes representing the structure are printed from the rear towards the front. Because of the way PostScript is designed the result will be the visible outer surface of the structure. The resulting PostScript program will be discussed in chapter .

The interesting parts of the conversion program is the projection from a three-dimensional space to a two-dimensional subspace. This is done with two macros in the program. These are

```#define xcoord(a,b,c) (b*coord(a,b,c)*SINBETA)-(a*coord(a,b,c)*SINALFA)
#define ycoord(a,b,c) (c*coord(a,b,c))-(a*coord(a,b,c)*COSALFA)-(b*coord(a,b,c)*COSBETA)```
xcoord(a,b,c) and ycoord(a,b,c) are the x- and y-coordinates of the three-dimensional point with coordinates (a,b,c). ALFA and BETA are the angles shown in projection. SINALFA, COSALFA, SINBETA and COSBETA are the sinus and cosinus values of these angles. This projection method does not use any algorithms for simulating perspective. The necessary calculations had to be done by the printer and this failed because the printing process took too long time (timeout error from the printer). Attempts to create the image directly in the computer were also made, but this was never finished.

Thomas Walmann
Fri Apr 7 16:34:05 METDST 1995