Question about ground control scene attribute, what is "uncertain"

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Ryan Avery

• May 28, 2019 20:24

What constitute "uncertain" for this attribute? 3 pixels off? 10 pixels off? It would be helpful to have a numerical representation of positional accuracy rather than a boolean so that we could filter by the positional accuracy we need. From https://developers.planet.com/docs/api/psscene4band/

ground_control

Positional accuracy of the item. If the item has uncertain positional accuracy, this value will be false.

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  Frank Warmerdam

  • May 28, 2019 20:35

  Ryan,

  We are not currently able to give a great metric for positional accuracy.  If ground_control is True we believe we are within our positional accuracy specification, while when it is False we are not at all confident.  It will be set to False in a number of cases:

   - we only have original satellite pointing information (often hundreds of meters off)

   - we only have positioning based on correcting the satellite pointing based on nearby scenes tie down. 

   - we only have control points tieing this scene to neighbours, but none directly to the ground reference. 

   - or lastly we only have a few tiedown points and our trust level in the result is low.

  If things being off by more than 10m is a problem, you should exclude anything with ground_control set to False.  We are contemplating offering more granularity of positional accuracy in the future, but we are still reviewing what would be possible and helpful.

   

  Best regards,

  Frank

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  Ryan Avery

  • May 28, 2019 23:52

  Thanks Frank! we noticed a few outlier scenes over Ghana that were about 10 pixels or >30 meters off, we will try the boolean filter. 

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