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Author Topic: Processing photos with several bad geotags  (Read 397 times)

SynGeo

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Processing photos with several bad geotags
« on: November 24, 2021, 07:46:33 AM »
I recently did a job using an aircraft equipped with dual 64Mpix cameras. An external L1 gps geotagger was used but ran into some problems.  The aircraft flies a line, taking a picture every second or so.  At the end of the line, the camera is shut off, the airplane maneuvered to the next line, camera back on, etc.  It is a manned UAV, able to map larger areas and we routinely collect several thousand images.  Occasionally, the camera's buffers will fill and the front and aft cameras will miss commands to trigger.  This results in a rather large mess, as the two cameras will have a different number of pictures.  Ultimately this results in a progressively large error in the geotags, especially when reversing lines.  We use lots of GCPs...

Our process has been to do an initial alignment using source, find as many GCPs in the photos as possible, uncheck the images, and re-run the alignment.  This works pretty well, but occasionally, and entire line will be off on the geotag and will end up floating in space.  When mapping non-descript terrain it can be difficult to find good tie point locations. 

Is there an better way to figure this out?

Thanks for your help.

Alexey Pasumansky

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Re: Processing photos with several bad geotags
« Reply #1 on: November 24, 2021, 04:28:16 PM »
Hello SynGeo,

Do you typically use Multicamera system approach to load the photos to Metashape project?

I think you can add correct pairs as multicamera system to one chunk, then add other images (with invalid GPS data) as single images (no multicamera system layout) to another chunk and clear the coordinate data there. Then use Merge Chunks command (prior to any kind of processing) and run Align Photos procedure in the merged chunk with Generic+Reference preselection. To the images with missing geotags Metashape will apply only Generic preselection criteria.
Best regards,
Alexey Pasumansky,
Agisoft LLC

SynGeo

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Re: Processing photos with several bad geotags
« Reply #2 on: November 25, 2021, 08:59:28 AM »
Thanks Alex.  I do use the multicamera set up frequently.  On this project, I screwed up and had a 28mm lens in one camera and a 55mm in the second.  Fortunately, I had plenty of overlap (80/80 cross grid) so each point shows up 30+ times.  I'm running each camera as a separate chunk, and will focus on getting the 55mm images to process the area completely.  I also had around 50 GCPs on the ground.  I've managed to find all of the GCPS.  I've deselected the cameras and re-run the align photos command several times, with each round of processing finding and correcting errant images.  I've added manual tie points to attempt to chain the loose photos into place.