ODM parameter " gps-accuracy"

Hi there, we would like to share some findings about benchmarking the flag “ gps-accuracy” and have some questions regarding this parameter. We are using ODM version 2.8.4.

  • We benchmarked the parameter with independent high precision GCPs on a RTK survey and the decrease of the default value of 10 (meters) to 0.2 (meters) helped significantly to improve absolute geolocation accuracy. In other words, it seems to be benefitial in terms of absolute geolocation accuracy to lower the default value when appropriate.
  • We also experienced, that if the gps-accuracy value is lower than 2x the geolocation accuracy of a specific survey, the output orthophoto can become distorted and is not usebale. Use case: value set to 0.4 for a flight without RTK/PPK.
  • In our use case we get data from 3rd party pilots with different sensor types (RGB / MS) and different sensor models, which can be RTK/PPK corrected or not.
  • The ODM documentation says, that the gps-accuracy is setup automatically by GPS DOP (dilution of precision). We could see, that there exists a GPS tag in exif called “ GPSDOP”, but none of our tested raw images had that tag written into exif. Here a link that lists some (I think not all) GPS tags: GPS Tags

Resuming, our main question is:
How can we automatically setup the value correctly?
We have here some ideas and feedback from the power users would be very much appreciated to share with us; even if it is for only one of the following approaches:
• Pilot input: The flight mission software allows to be setup to write the GPS DOP of the mission as a tag into exif. This question is more directed to the pilots of this forum. Can this be done?
• If it’s not possible to push the GPSDOP info from the GPS exif tag, we would like to setup 2 ODM parameter templates with different gps-accuracy values, depending if the survey has RTK/PPK correction or not. We think about value “ 0.4” for RTK flights and keep the default value of “ 10” for surveys without RTK/PPK.
• The question is: are the proposed values (0.4 and 10) a good setup or do the ODM forum power users recommend different values?
• Is it possible to know, if a flight was RTK/PPK corrected, using the default exif / xmp info? There is a GPS tag called “GPSDifferential”, but we also couldn’t detect this tag in any of our tested raw images.
• Or is it possible to know, if a flight has RTK/PPK correction by knowing the camera/sensor model? Example: v2 dji fc6310r 5472 3648 brown 0.6666

Any feedback on one or more approaches is very much appreciated!

Best,
Gabor

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Relevant tags used to extract the GPS DOP:

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I’ve had good results (though not benchmarked. Just visual assessment) with 0.1 for the gps-accuracy for a Phantom RTK running on a CORS network.

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