Consider switching to gc_map2 program

[mcgarth]

We use GAMMA's gc_map1 program: https://github.com/GeoscienceAustralia/gamma_insar/blob/8c4dc16743a40888e1a438ca4dfa54c3ca84411c/insar/coregister_dem.py#L433

but gc_map1 was deprecated by GAMMA, and they recommend using gc_map2 instead.

See the following excerpt from the GAMMA GEO users guide:

6.2. Geocoding for tracks different from N-S direction In 2017 we added support for the geocoding of SAR data acquired in tracks clearly different from the north-south or south-north directions. Such data are acquired by the satellites in regions close to the poles (e.g. in Antarctica), as well as by airborne and terrestrial sensors. The program gc_map processes the data DEM line after DEM line which is not adequate when determining the layover and shadow mask – resulting in incorrect layover and shadow masks which are then potentially also used in pixel_area which will affect the quality of the geocoding refinement and of the terrain normalization of backscatter images. For most satellite data the heading deviates by less than 15 deg. from the north-south direction and consequently the related effects can be neglected. In cases where the deviation is larger, the new program gc_map2 should be used. This program determines the layover and shadow maps in the radar look direction and provides therefore a correct result independent of the heading. The slight disadvantage of gc_map2 is that it is slower than gc_map. For this reason gc_map is kept in the software.

[daleroberts]

Fixed now.