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Voyager View Demo

G. E. Malpas, Little Stoke, Bristol

My program simulates the view from Nasa's Voyager spacecraft on its approach to Saturn. It will run on both models of the BBC Microcomputer and demonstrates the high-resolution graphics and some of the plotting capabilities of the machine.

The first part of the program at subroutine 390 describes the program; note the use of double-height teletext characters using CHR$(141). Then the following data is read from the data file: R, the radius of the planet; M and N, the location of the planet on the screen; Inc, the angle of the rings; and finally Comp, the obliqueness of the rings.

Using this data, the planet is drawn but invisibly using the VDU 19 command in line 50 and then the drawing is complete the colour is applied to the plot in line 110. The rings are then drawn individually but each one is drawn in two halves using the PLOT 5 and PLOT 6 commands which produces a three-dimensional effect by making the plot transparent - lines 170 and 200. The completed drawing is then displayed for five seconds before the screen is cleared and the next frame is plotted.

The data supplied produces eight frames and shows a flight towards the planet, flying over the pole and then looking down through the ring structure. The data could easily be altered to produce different flight paths.

Apart from showing the graphics capability of the BBC machine, the program could be used in schools for teaching astronomy or could be used as the background for a game. However, the main problem with the program is that each frame takes about one minute to draw so it could hardly be described as animated motion.