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The color geometry test produces a graphical display of geometry errors. Normally, with the Test option OFF, a ray is traced from the viewpoint to the geometry, terminating at the first nontransparent surface encountered. The angle of incidence of the ray with the surface normal determines the intensity of the pixel, while the cell on the other side of the surface determines the color. With the Test option ON, the pixel color and intensity are set initially from the first encounter as without testing. The ray is then continued until it exits the geometry model or an error is encountered. If so, the color of the pixel is changed to the error color (default red) and the intensity of the error color is computed from the angle between the ray and the normal of the surface where the error was first encountered. The geometry error has priority over correctly defined geometry, which might otherwise obstruct the view to the error. The volume containing the geometry error is thus highly visible and easy to locate.
Since geometry checking follows rays through the entire model, it requires more computer time than without checking. The computer time can be reduced by lowering the color resolution or decreasing the size of the graphics window or subwindow, but the completeness of the geometry test is also diminished. A model defined in surface geometry usually requires more time to check than the equivalent model in a body description.
To use the Color test option, check the Test item in the Options menu or type TEST ON and then Color. The usual requirements for ray tracing must be met-a finite spatial window and at least one cell must be nontransparent.