photrim

The photrim program trims pixels outside of the phase, incidence, and emission angles by setting them to "null" within all bands of the cube. A user can either trim using the program's default method or the USEDEM method.

By default, photrim uses the angles calculated from the ellipsoidal surface to trim an image. The ellipsoid is retrieved from the IAU/NAIF target body file, which is defined within the cube's kernel group as the TargetAttitudeShape. If the USEDEM option is selected, then photrim will use the angles calculated from the digital elevation model (DEM) to perform the trim instead. The DEM is referenced in the ShapeModel keyword within the input cube's kernel group. Note that photrim does not trim using local slopes.

Angle Definitions:

Phase Angle - The angle between the sun vector to a point on the ellipsoid and the instrument vector to the same point.
Incidence Angle - The angle between the sun vector to a point on the ellipsoid and the normal at that point.
Emission Angle - The angle between the instrument vector to a point on the ellipsoid 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 an ellipsoidal body cannot be illuminated if the incidence angle is greater than 90 degrees.

4) A point on the surface of an ellipsoidal 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.

This is an example of trimming an ISIS cube without accounting for the DEM. Instead, the program will trim the cube based on the ellipsoid.

photrim FROM=AS15-M-1499_msk-L2_1250mpp.cub TO=photrim_no_dem MAXEMISSION=88

Example Gui

Example GUI Screenshot of the photrim GUI with a max emission angle of 88. The reset of the parameters are set to the program defaults.

Input Cube

Input Cube Parameter Name: FROM The untrimmed cube. This is an oblique view of the moon acquired by the Apollo Metric camera.

Output Cube

Output Cube Parameter Name: TO The result of trimming the cube using the ellipsoid model and a max emission angle of 88.

This example shows the result of trimming an ISIS cube while accounting for the digital elevation model of the cube.

photrim FROM=AS15-M-1499_msk-L2_1250mpp.cub TO=photrim_dem USEDEM=TRUE MAXEMISSION=88

Example Gui

Example Gui Screenshot of the photrim GUI with a max emission angle of 88 degrees and with the option to use the digital elevation model selected. The rest of the parameters are set to the defaults.

Input Cube

Input Cube Parameter Name: FROM The untrimmed cube. This is an oblique view of the moon acquired by the Apollo Metric camera.

Output Cube

Output Cube Parameter Name: TO The result of trimming the input cube using the DEM and a max emission angle of 88 degrees.