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Optionally generate orthos on DTM

Overall, I’ve been very impressed with Pix4D’s ability to generate really nice orthos on digital surface models. True orthos are great when they work, and the software (particularly since v2.0) is really adept at doing it right around well defined features, such as buildings. That said, rough and less defined things seem to cause a lot of trouble.

For example, I’m working on a farm test site that has a few buildings, fields and some trees. Without much effort, the buildings look great. The trees, on the other hand, are causing me a lot of trouble. The MosiacEditor doesn’t help much here. I’ll likely have to do the processing in different software. Since it doesn’t do well truly modeling the trees–something that is just accepted in photogrammetry–it would be far better to be able to model such features on a cleaned surface model (DTM) rather than a surface model (DSM).

Consider the trees below. Pix4D’s ortho looks like this:

When it should really look more like this:

I’d like to see more tools available to generate orthos on a bare earth model, whether that’s a DTM that’s created inside Pix4D or one that is imported from elsewhere. In the meantime, I believe I’m going to have to use other software to generate orthos and mosaics.

Wes, you can import a DTM into Pix4D but if you use it to create an ortho you may get really weird results. Pix4D uses the elevation of the DSM to then color each pixel according to all of the pictures that include that 3D point so using a DTM to create the ortho where there is a tree could cause a lot of noise.

Have you tried using the orthomosaic editor to select the area around the tree and project it in planar instead of ortho? That way you use one of the original pictures instead of blending the colors based on the DSM.

Curious to hear what happens if you get a chance to run it with the DTM, but I don’t think it will yield good results.