The "x" option at the Main Menu will turn on shadow masking. This is something you will want to do since you do not want shadows to be interpreted as topography. The extract filter, which is almost always used, performs several functions:
- It enhances shadows by extending them into the lit portion. This is done because shadows are not sharp, particularly if the image is lower in resolution than the maplet, and this is interpreted as topography by the LITHOS software.
- It zeroes out data in regions that, according to the current maplet topography, should not be seen in an image. In many cases the maplet is seen obliqely in the image and some areas, especially the bottoms of craters, cannot be seen. This is done with both a restriction on emission angle and through ray tracing.
- It zeroes out data in regions that, according to the current maplet topography, should not be in shadow. This is done through ray tracing.
LITHOS will ask you to enter the tolerance; .025 is the standard input.
Main Menu: Q 0123O IUCRSG NVAMBX DEPL FZH? x >x enter tolerance .025 Current landmark = EE0001 SCALE = 0.000100 QSZ = 49 Lat/Lon/Rad = -6.806 264.097 0.266 Region = EE gc LMRK_DISPLAY0.pgm gc LMRK_DISPLAY1.pgm check display Main Menu: Q 0123O IUCRSG NVAMBX DEPL FZH?
== Standard Input ===
x .025