Viewer is a program to draw three-dimensional surfaces of the form z = f(x,y). The function f and the boundary values for x and y are the inputs. The surface thus defined may be drawn after arbitrary rotations.
The method used is division into a uniform rectangular grid of the given x and y ranges. The values of the supplied function at the grid points (x, y) are calculated and stored; this defines the surface. The surface is portrayed by connecting successive (y,z) points with straight-line segments for each x value on the grid and, in turn, connecting successive (x,z) points for each fixed y value on the grid. These lines are then projected by parallel projection onto the fixed yz-plane for plotting.
This program was released by NASA through COSMIC as LAR-11049. The italicized text above is from the official NASA release.
The program has been modified by PDAS to produce a file called viewer.gnu that may be used with gnuplot. For example
gnuplot>plot 'viewer.gnu' with lines
The name of the program has been changed from PLOT3D to Viewer to avoid confusion with a popular NASA Langley program.