Crater Shadows Simulator - fermigas/ltvt GitHub Wiki
Downloads.. Utility programs..
This freeware program plots the profiles of cylindrically craters using either a mathematical formula or a disk file defining the variation of depth with radial distance from the crater center. It then predicts what the shadow pattern inside the crater should look like if the crater were a flat surface and illuminated by a point source at a specified sun angle.
- The program executable file is available for download under Utility programs.
- Detailed directions are included in the Readme.txt file in the download.
- v1.2 - uploaded 12 Nov 2008 includes a new control to optionally modify the profile to conform, approximately, to the three-dimensional curve of the Moon's surface as a function of radius from the feature's center. The views are still from directly overhead. See the Readme.txt file for details.
Four preset mathematical profiles are available, each of which can optionally include a section of flat floor at the center:
The program can also read a completely arbitrary profile from a disk file. In this case it is plotting measurements of the depth of the crater Linné as a function of distance from the crater center as measured by LTVT on an Apollo 15 Metric image:
The following figure shows the subtle, and sometimes no so subtle, differences in the expected shadow patterns for the simple mathematical shapes available in the Simulator when illuminated at the same sun angle. The exact results (and the results for the different shapes compare) will depend on the assumed Depth/Diameter ratio.
As can be seen, when viewed from overhead, a spherical bowl gives a straight-edged shadow when the sun angle is 45°. This turns odd to be true regardless of the Depth/Diameter ratio, although the fraction of the bowl occupied by the straight-edged shadow will still depends on that. Exactly half the bowl is filled (i.e., the shadow bisects the rim's circle) when the Depth/Diameter ratio is 0.5, corresponding to a complete hemisphere (with vertical walls at the rim).
This page has been edited 6 times. The last modification was made by - 
JimMosher on Nov 12, 2008 3:23 pm