Work continues to build a SGP4 object implementation on propeller. Getting the mathematical expressions correct is at best painful. I have been converting a C language implementation into spin little by little. I have written some utilities to assist with that conversion and progress is more quick now and less error prone (I hope). I use the FPU utilities provided to convert the math expressions into FPU assembly language and then run through my utility to convert that to spin.
I could really use some insights into how to validate the results. I can of course always compare results against the version I am converting from, but who is to say that it is correct? Ideally there would be a standard test kep set and a standard observation location that would create known results that could be validated.
The SGP4/SDP4 specification does speak to this a bit, but my understanding of it is not yet adequate to evaluate. If anyone has insights here, I could use some advice.