Implement accurate and flexible fiberloss calculations

dkirkby commented 8 years ago

This is not ready to merge yet but is getting close. Here is the final checklist:

[x] Add support for point-like sources.
[x] Anti-alias fiber aperture.
[x] Read and use file of optional achromatic centroid offsets.
[x] Add option to save pre-tabulated fiberloss for later use w/o galsim.
[x] Review documentation of new features.
[ ] Compare with fiberloss files in desimodel.
[ ] Optimize numerical parameters num_wlen, num_pixels.
[ ] Add some unit tests of new features.

The goal of this PR is to obtain correct results at the required level of realism. Optimizations for efficient calculation of a large number (~5K) of sources distributed over the focal plane in a single exposure are not considered here.

dkirkby commented 7 years ago

The new fiberloss module can now save the results of an on-the-fly galsim calculation to a file with the same format as used in desimodel, so we have a mechanism to update the files desimodel/data/throughput/fiberloss-xxx.dat to be more realistic, if we want to.

dkirkby commented 7 years ago

I am going to close this now (and defer the last 3 items in the checklist) in order to have a stable base for working on #6.

desihub / specsim

Implement accurate and flexible fiberloss calculations #52