photrim

Given a camera based cube and minimum and maximum ranges for the phase, incidence, and emission angles, this program sets any pixels outside these ranges to NULL. Photrim uses angles calculated from the spheroid; it does not use local slopes.

Angle Definitions:

Phase Angle - The angle between the sun vector to a point on the spheroid and the instrument vector to the same point.
Incidence Angle - The angle between the sun vector to a point on the spheroid and the normal at that point.
Emission Angle - The angle between the instrument vector to a point on the spheroid and the normal at that point.

Examples of special cases:

1) If the instrument is directly between the point and the sun, then the phase angle is 0; if both the sun and the instrument are both along the normal to the point, then the phase, incidence and emission angles are all zero.

2) If the instrument is looking along the normal and the sun is illuminating the point, then the emission angle is 0 and the incidence and phase angles will be in the range of 0 to 90 and equal to each other.

3) A point on the surface of a spherical body cannot be illuminated if the incidence angle is greater than 90 degrees.

4) A point on the surface of spherical body cannot be visible if the emission angle is greater than 90 degrees.

5) If a point is both illuminated and visible, then the phase angle ranges from 0 to less than 180.