Ortho photos over water

We are taking multi-spectral images using a DJI Phantom over water to estimate chlorophyll distributions. This means that the image matching algorithms do not work because the waves move between images.

We can do PPK processing to have more accurate drone positioning.

We do not need the images to be exactly placed - they can be off in the horizontal. Because we are over water, the terrain is flat.

Is there a way to generate approximately image placements for each image? It would be great if we coudl do a mosaic from ODM, but if each image could be “placed” (e.g., a geoTiff), we could load the images into QGIS or other software for mosaicing.

Essentially, if we assume the terrain is flat, can ODM read the GPS locations, pitch-roll-yaw of the drone, and pointing anglers from the gimbal and generate an approximate ortho image?

Gus

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Hmm… Not sure we can force the pipeline into doing that.

What are your typical processing parameters?

I’d say if something like Microsoft Image Composite Editor or Hugin can’t stitch it naively, that we’d have trouble, as well, unfortunately.

Thank you for the quick reply. However, neither Hugin or Microsoft ICE will work because they both depend on finding matching locations in the image files.

I was hoping that ODM did a preliminary old-school orthophoto calculation to show where the photos are relative to each other (an outline of the photo boundaries) or a calculation where the images are roughly laid out so the image.

Essentially, since my images do not have any matching points (they are over water with waves), i need to be able to warp each image based on the camera position, the pitch-role-yaw of the aircraft, and the pointing angles of the camera.

Something similar to this stack overflow question:
matlab - Transform Image using Roll-Pitch-Yaw angles (Image rectification) - Stack Overflow, except I also need to locate the image in space.

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Maybe this new mode in our pipeline might fare better with your particular data once it lands:

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The images look like exactly what i need, just a rough placement of the drone photo in geolocated space.

Will there be a way to export this information for each photo? It would be nice if it just could create geoTiffs.

Thanks for your help.

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I don’t know how this will work yet! Good questions, however.

Piero is still testing, developing, and implementing this.

I have a similar application (over water).

I found the “import photo” plugin in QGIS does what you are asking (“a rough placement of the drone photo in geolocated space.”). Uses the Exif data.

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Sorry - I mentioned the wrong QGIS plug in. The one you want is “Vertical Photo Placer

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Thank you for the pointer, I’ll try the QGIS plugin

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Hi- my work involves a lot of direct georectification of aerial imagery over water. I am just starting with ODM, but I have been using Agisoft for several years now. Here’s my current workflow for drone images over water:

  1. Fly the drone over the beach and acquire images with large overlap.
  2. Use the images to compute the intrinsic camera parameters
  3. Fly my water mission and use the intrinsic parameters to correct for distortion
  4. Use image exif data for approximate direct georectification with the undistorted images. Largest sources of error are heading and altitude.

Note that you need the height above the water, and DJI altitudes are unreliable, so I take a picture as close to the water level as I dare (if flying), or I have my VO hold the drone right above the water and take a picture.

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Do you have any code or procedures to do the image correction?

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