sunmoonpos: import some of the SOFA C library #583
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for a better estimate of the sun and moon positions. The original C code is add in lib/sofa/src/ and the bundle of functions used are added together in src/sofa.c
Function arguments that are not modified are declared as const. Static local variables and data that were effectively constants are declared as const to make it clear that there is no thread safety issue.
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for a better estimate of the sun and moon positions.
The original C code is add in lib/sofa/src/ and the bundle of functions used are added together in src/sofa.c
Noticed that the sun and moon position did not agree well with that from SOFA, and these are inputs into some of the tide displacement calculations and it can make a significant difference to the tide displacements.
This PR is a possible alternative using the SOFA C library. Just a few files from this library, bundled into a single file src/sofa.c to keep the build simple. Alternatively the SOFA library could be built and linked separately, but having tried both approaches it seems simpler to just bundle the few functions into a single file. The original code is placed in lib/sofa/src/ for reference.
Also noted that these return the ECI position and this still needs to be convert to ECEF using eci2ecef() and this also appears to be a little off, but the differences for eci2ecef() appear to have a negligible impact on the tide displacements.
Does anyone care enough about the sun and moon position to bother with this?
Is using SOFA a useful approach?
Any strong opinions on bundling the few functions into one file vs building a separate library?