GACOS: Error due to lat/lon and UTM coordinates for HYP3 products

[Sugeradi985]

Description of the problem
An error occurred when I used Mintpy to do atmospheric correction (GACOS) on the interferometric pairs derived from HYP3 sdk.

I think it is the coordinate system differences that mattered but not sure, and GACOS data (WGS84) cannot be read normally when processing interferometric pairs (WGS84 UTM50N) derived from HYP3 sdk.

******************** step - correct_troposphere ********************
Input data seems to be geocoded. Lookup file not needed.
tropospheric delay correction with gacos approach

tropo_gacos.py -f /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/timeseries.h5 -g /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/inputs/geometryGeo.h5 -o /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/timeseries_GACOS.h5 --dir ./GACOS
Use GACOS products at directory: /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/GACOS
update mode: ON
output file: /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/inputs/GACOS.h5
1) output file either do NOT exist or is NOT newer than all ZTD files.
run or skip: run
--------------------------------------------------
create HDF5 file: /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/inputs/GACOS.h5 with w mode
create dataset  : date       of |S8                       in size of (120,)               with compression = None
create dataset  : timeseries of <class 'numpy.float32'>   in size of (120, 2799, 3591)    with compression = None
close  HDF5 file: /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/inputs/GACOS.h5
read incidenceAngle from file: /mnt/hyp3_mintpy_asf/bj_142_126/newds/mintpy/inputs/geometryGeo.h5

Full error message

Traceback (most recent call last):
  File "/home/melon/tools/MintPy/mintpy/smallbaselineApp.py", line 1279, in <module>
    main(sys.argv[1:])
  File "/home/melon/tools/MintPy/mintpy/smallbaselineApp.py", line 1261, in main
    app.run(steps=inps.runSteps)
  File "/home/melon/tools/MintPy/mintpy/smallbaselineApp.py", line 1054, in run
    self.run_tropospheric_delay_correction(sname)
  File "/home/melon/tools/MintPy/mintpy/smallbaselineApp.py", line 791, in run_tropospheric_delay_correction
    mintpy.tropo_gacos.main(iargs)
  File "/home/melon/tools/MintPy/mintpy/tropo_gacos.py", line 361, in main
    calculate_delay_timeseries(tropo_file=inps.tropo_file,
  File "/home/melon/tools/MintPy/mintpy/tropo_gacos.py", line 306, in calculate_delay_timeseries
    delay = get_delay_geo(ztd_file, atr, cos_inc_angle)
  File "/home/melon/tools/MintPy/mintpy/tropo_gacos.py", line 129, in get_delay_geo
    delay = resize(delay, (length, width),
  File "/home/melon/tools/miniconda3/envs/insar/lib/python3.8/site-packages/skimage/transform/_warps.py", line 176, in resize
    out = warp(image, tform, output_shape=output_shape, order=order,
  File "/home/melon/tools/miniconda3/envs/insar/lib/python3.8/site-packages/skimage/transform/_warps.py", line 827, in warp
    raise ValueError("Cannot warp empty image with dimensions",
ValueError: ('Cannot warp empty image with dimensions', (0, 0))

System information

• Operating system: Linux-Ubuntu 18.04.5
• Python environment: conda
• Version of MintPy: MintPy release version v1.3.1

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[yunjunz]

Thank you @Sugeradi985 for reporting this bug. I agree with you that it's due to the different coordinate systems between GACOS and HyP3 products. I would suggest the following two solutions:

1. crop the GACOS products based on the SNWE of HyP3; then resize the 2D matrix. The step by step procedure would be:

• grab the four corner coordinates of the HyP3 products in UTM;
• convert them to lat/lon using ut.to_latlon();
• use these lat/lon to read/crop the GACOS products;
• resize the cropped GACOS products to the same size as the HyP3 products using skimage.transform.resize(). Check similar usage in tropo_gacos.py#L128 for reference.

2. resample the 2D matrix from lat/lon coordinates to UTM coordinates.

• calculate the pixel-wised coordinates of HyP3 products in lat/lon using ut.to_latlon()
• resample the GACOS 2D matrix from its original lat/lon grid to the lat/lon coordinates calculated above.

Option 1 is used in tropo_pyaps3.py currently. Option 2 is definitely the right way, but can be slower and slightly more complex than option 1. I am not 100% clear about the difference between the two.

[mosyhey]

You need to add this piece of code to tropo_gacos.py, line 120 (after geo_box part):

    ########## New lines for converting utm to lat/lon (https://github.com/insarlab/MintPy/issues/664)
    strProcessor = atr['PROCESSOR']
    if strProcessor == 'hyp3':
        import utm #Install utm as "pip install utm" if not installed
        strUtmZone = atr['UTM_ZONE'] #Read from metadate, for example: "11N"
        intUtmZone = int(strUtmZone[0:-1]) #In this example: 11
        strHemisphere = strUtmZone[-1] #In this example: "N"
        north, west = utm.to_latlon(geo_box[0], geo_box[1], intUtmZone, strHemisphere)
        south, east = utm.to_latlon(geo_box[2], geo_box[3], intUtmZone, strHemisphere)
        geo_box = (west, north, east, south)
    ##########

Be aware that there is a very small and negligible rotation in converting a shape from UTM into Lat/Lon coordinate system.