GCP location error

This topic contains 9 replies, has 2 voices, and was last updated by  cnu_lee 2 years, 3 months ago.

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  • #849


    Hi professor,

    In the “GCP selection” module, no matter I choosed “keep current orbits” or “through external DEM”, the result of “Mean kml” has shown the location of automatic GCP was not matched with my study area and was too far away .And the amplitude map was far away from study area in Google earth ,but they couldn’t be displayed in the same screen. I don’t know why is this, my DEM data is SRTM, my dataset is 11 scenes Radarsat-2 images.

    Thanks, hope your reply.


  • #850


    In the GCP selection module there is a flag: ‘OVW’ which stays for “overwrite”.
    If you do not flag it, it will load the previous “mean kml” map.
    Since you are not the first one asking about it, I switched it to checked as default…
    You’ll get it in the next version, for the moment just check it manually.

  • #873


    Thanks for your reply.

    I went back and extract the master area again, but I found the SAR image of extracted master area isn’t the area that I want. The centre of wrong area isn’t what I input in “latitude” and “longtitude”, but is the centre of one complete image. And I set the “latitude” and “longitude”, but the “samples” and “lines” doesn’t change.

  • #874


    if you start the SLC processing over again,
    the Master and all previously generated files are overwritten.
    Also, the Master area is set as default: center in the middle of the scene.
    So, you have to set the Master area again. By the way, these operations were slightly improved recently: download the last version (or check in the updates history the version you are using is already containing the improvements).

    • #875


      The version of software is May 6.

      I delete the old folders and import the data again.I set the master area again in “longitude” and “latitude” ,but the error was still here. The center of master area was still the center of the scene.By the way, the master area of kml format was right, but the SAR format image was not matched with the kml file.

  • #876


    Can you please grab a few screenshots to show us your case?

    • #877


      The first picture is SAR image,the other one is kml format master area.It’s obvious to find that area on the two pictures don’t match.

    • #878


      I’m sorry for that the two pictures couldn’t be uploaded successfully.These two ones are new.

      You must be logged in to view attached files.
  • #881


    A possible explanation is a wrong timing of the image relative to the orbital data.
    Suggestion: plot the footprints of the full-frame, extract the full-frame Master and plot it.
    Based on the 2 pictures, you can make a rough estimation of the shift between the real geographic location of the image and the apparent one retrieved from the orbits.
    You can then proceed in 2 different ways:
    either you make use of the estimated shift to extract your area of interest (you have to shift the apparent Master area center)
    or you extract and coregister the full-frame, and later you extract a sub-dataset over the area of interest (from the site processing module).
    This misgeocoding can be later corrected through the GCP.

    check please if the software returned a message like “warning, the geographic center of the image retrieved from orbital data does not match …”.
    We can check whether we can in some ways improve/correct it or not.

    • #882


      I don’t understand how to process specifically,but I found Matlab gave me a message”center latitude and longitude from MASTER SLC data differ from center of calculated footprint”. Is this message important for this problem?

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