Added constant in ramp.py

[bjmarfito]

Description of proposed changes

Added estimation and removal of constant in ramp.py

Reminders

• [ ] Fix #xxxx
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[yunjunz]

@bjmarfito could you describe your motivation for this addition? Note that since InSAR products are relative in space, we always keep the value at the reference pixel (specified with REF_Y/X) to zero as below, thus, will remove the effect of the estimated constant from this PR.

https://github.com/insarlab/MintPy/blob/5ca554fef324b816f9130feec567e2cf463e41d2/src/mintpy/objects/ramp.py#L110-L114

[bjmarfito]

Hi @yunjunz, sorry, I missed this part of the code. My motivation for introducing this constant deramping is to estimate it using the the whole or part of the interferogram and not just using a reference point. Please correct me if my way of thinking is wrong.

[yunjunz]

Hi @yunjunz, sorry, I missed this part of the code. My motivation for introducing this constant deramping is to estimate it using the whole or part of the interferogram and not just using a reference point. Please correct me if my way of thinking is wrong.

Hi @bjmarfito, no need to be sorry at all, I appreciate your effort of contributing back! From my understanding, the "constant deramping" is to estimate a global mean, which is intended to do spatial referencing using the global mean. I don't really recommend that personally, as it makes the interpretation complicated: there is no exact location for this spatial reference, and it could change as the dataset spatial coverage change.

On the other hand, this is a subjective choice, it's totally fine with me if you still want it in the code, just make sure you remove the REF_Y/X attributes before you run this constant deramping, to turn off the re-referencing effect from the mentioned code above, in a different (maybe your own) script. At this point, I would prefer not to add this attribute removal automatically within this script for the cautious reason, so that regular users won't use it by accidence without being fully aware of this.

[bjmarfito]

Hi @yunjunz, thank you for your insights. Based on your recommendations, I think it is better for me to write my personal code for this as to not confuse the other users of this package.

I will close this PR.