Allow GPS class to work with other image projections

[scottstanie]

Description of proposed changes

• Added two general purpose functions useful for interacting with projections other than EPSG:4326:
  • reproject convert X/Y coordinates between different EPSGs. It's more general than some of the other UTM conversion functions- for instance, to_latlon can now just call the reproject function to do the conversion.
  • get_image_rowcol to find the pixel location nearest to some lat/lon location
• Both functions are used in the GPS class to convert the gps station locations in lat/lon to whatever the image projection is, stored in the EPSG attribute
  • Future note- I've also used this in a change to tropo_pyaps.py to run that script on non-EPSG:4326 images. That will be submitted after

Reminders

• Partially addresses insar_vs_GPS comparison with geometry in geographical coordinates #1010
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[yunjunz]

Thank you @scottstanie for the PR! My main comment is the get_image_rowcol(): since it relies on mintpy.objects.coord.coordinate.geo2radar(), and mintpy.objects.coord.py relies on mintpy.utils.utils0.py, I would suggest moving this function into mintpy.objects.coord.py to avoid the circular imports. You could find the complete reliance info among sub-modules in mintpy here. The possible location could be:

• as an independent function as it's now OR
• inside geo2radar() OR
• inside lalo2yx()

UPDATE: If we assume the InSAR file is already geocoded (in EPSG:4236 or other projections), then merging geo_iamge_rowcol() into lalo2yx() sounds the simplest to me. What do you think?

Could you also rebase this PR against the latest main branch?

[yunjunz]

utils0 is imported within util1 already, so we don't need an extra utils0 as ut0 here. This is a messy part in mintpy, and the current logic is: 1) utils1 imports everything from utils0; 2) utils imports everything from utils0 and utils1.

[yunjunz]

This function is not used currently anywhere, so it's fine with me. For your information: from my experience, given a GNSS site, we either interpolate InSAR or average multiple InSAR pixels around the GNSS site. Personally, I have not gotten a good result yet by comparing GNSS and its nearest InSAR pixel yet.

[yunjunz]

I am just curious: in this syntax, when will the np.nan value be returned? Is it the same scenario as the raise ValueError above?