Calculate LOOK_REF1/2/3/4 from attributes and dataset of geometryRadar.h5 files

[ranneylxr]

Kite support products generated by Gamma, Matlab, ISCE, GMTSAR, ROI_PAC and SAR scape.
Mintpy uses roi_pac and isce as processor. If the processor is ROI_PAC, we can just use the save_roipac.py to generate datafile and parameter file(*.rsc). But if the processor is ISCE, we have two solutions: 1. calculate LOOK_REF1/2/3/4 from attributes and dataset of geometryRadar.h5 file. 2. write a script to generate *.unw.geo, *.unw.geo.xml and los.rdr.geo files based on the results of mintpy.

Issue 1 (For solution 1):
Based on the ROI_PAC document and IntSim.f script, Calculation method of LOOK_REF1/2/3/4 is:
look_angle = acos((sc_d^2+range^2-target_d^2)/(2sc_drange))
where range is slant_range; target_d = img_pln_rad; sc_d = img_pln_rad+spacecraft_height;
img_pln_rad is earth radius assuming spherical earth.
From IntSim.f script, a conclusion can be drawed that the calculation of img_pln_rad needs many parameters. Some of them can be found in attributes or dataset of *.h5 file. Some parameters like "spacecraft position vector", "body fixed state vector" can not be found in the results of mintpy. Thus, it seems that solution 1 can not be achieved. This is the first problem I met.