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insarlab / MintPy

Miami InSAR time-series software in Python
https://mintpy.readthedocs.io
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GPS Stations as "Tie Points" instead of Reference Points #708

Closed rbiessel closed 2 years ago

rbiessel commented 2 years ago

I'm not sure I really understand the reference point selection when displaying a velocity map. From what I understand, the velocities are referenced to some point, as opposed to re-referencing the time series and recomputing the velocity map? It also seems then that --ref-gps option sets the velocity at that point to zero, regardless of the actual velocity of that station.

I would like to be able to reference the initial time-series to a GPS station and I would like to be able to use it as a tie point rather than simply a reference point. In other words, I want to be able reproject GPS station components in the same way (enu2los or up2los) and then adjust the InSAR time-series so it agrees with this GPS station. (Going even further, it would be great to be able to either interpolate tie-points between different GPS stations or fit a least-squares plane to reference the InSAR timeseries to.)

In other words, I would like to be able to fix the InSAR time-series to some GPS time-series instead of simply using a GPS station velocity as a reference.

For environments with very spatially heterogeneous surface movements where it's find any pixel that is actually stable, this would be quite useful.

I want to get around to implementing this into MintPy myself, but I thought I'd suggest it here if anyone is planning on doing something similar already in the meantime.

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yunjunz commented 2 years ago
  1. re-referencing the velocity from point P to Q
  2. re-referencing the time-series from point P to Q, then re-calculate the linear velocity

The resulting linear velocities are exactly the same between 1 and 2. @olliestephenson and I confirmed this via math and real data experiment.

I'm not sure I really understand the reference point selection when displaying a velocity map. From what I understand, the velocities are referenced to some point, as opposed to re-referencing the time series and recomputing the velocity map? It also seems then that --ref-gps option sets the velocity at that point to zero, regardless of the actual velocity of that station.

Your understanding is correct.

yunjunz commented 2 years ago

@rbiessel Your idea of tieing the InSAR time-series or velocity to GNSS via one or multiple tie points sounds all good to me. I am happy to answer any questions related to MintPy that you may have.

You may want to implement it in a jupyter notebook or eventually an independent script, I would not suggest integrating it into view.py as it's pretty complicated there already.