Enhancement: Use coherence to identify best reference pixel

[mcgarth]

Use amplitude or coherence image to detect a pixel/region that is always bright or always coherent in the interferograms. This indicates low phase noise and relative stability

[basaks]

reference pixel calculation has been there for a while and recently updated to match that of Matlab's reference pixel calculation. Discuss with MG before closing.

[basaks]

Specifically look at the changes in these functions:

refpixel._step
refpixel.ref_pixel
tests/test_refpixel.test_refnxy_step_1

[basaks]

Matt and I agreed to close this.

[mcgarth]

Reopening: The original enhancement has not been implemented yet, since it will use coherence and/or amplitude images that are not currently read in to PyRate.

[sheecegardezi]

New functionality has to be added at: https://github.com/GeoscienceAustralia/PyRate/blob/53cf14fcbb2fc44bf47a3522c5270dc3a61e3ade/pyrate/process.py#L144

[mcgarth]

Coherence data is now read in prepifg and would be available for this enhancement