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I have a video footage shot on an iPhone 8, that I want to track and use in Blender (to add objects etc.). I added a couple markers and these track pretty well, I can get a fairly low solve error (under 0.3).

The problem is that the ground plane keeps slipping off from its original position in the 3D scene. I tried a couple different camera settings (settings only sensor width, both width and focal length, various refine options), but the result is never satisfactory. Since this is the first time I am trying tracking, I might be missing something here. Another problem might be that the video is actually shot in portrait not landscape.

I uploaded both the project file and image sequence compiled into an archive here https://drive.google.com/file/d/1hn30fjg09rlZt3wLz0bfsWwe_oraut1q/view?usp=sharing. It is unfortunately quiet large because of the png images.

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    $\begingroup$ I'm not going to download files from a site plagued with adds or that I can't trust, But The most common error is this: the shot has no parallax. Meaning that the camera is stationary, it is just rotating, but with no displacecement. Shots like those cannot be solved with the default solver, but need to be solved as tripod. Read: blender.stackexchange.com/questions/42329/… $\endgroup$ – susu Sep 29 at 20:42
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    $\begingroup$ blender.stackexchange.com/questions/58098/… $\endgroup$ – susu Sep 29 at 20:44
  • $\begingroup$ @susu understandable. Thanks for posting the links, I actually already read both and I am in fact using tripod tracking the whole time. $\endgroup$ – davidv Sep 30 at 4:53
  • $\begingroup$ @susu I did reupload to my Google Drive, if that makes it comfortable enough for you to take a look (link is in the original question). $\endgroup$ – davidv Sep 30 at 5:34
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The most common error is this: the shot has no parallax. Meaning that the camera is stationary, it is just rotating, but with no displacecement.

enter image description here

Shots like those cannot be solved with the default solver, but need to be solved as tripod. Read:

How can I get better results when doing camera motion tracking?

A few words of advise: track objects at the point where there is more contrast, like the window on the back, don't track the middle where all of the pixels have almost the same value, track a sharp edge or features that show distinct characteristics.

enter image description here

In this case the tracking is accurate and the tripod solution is as good as it is going to get, but know this: you will never get 3D reconstruction out of a tripod solve. You will only get a camera movement that resembles that of the original camera. Without parallax there is no way to estimate depth, meaning how far away objects are from the camera. The tracker for the window across the freeway will end up at the same distance from the camera as the trackers for objects in the foreground.

The tracking points are projected into a sphere around the camera, there is no distance information. So in this case you need to be vary careful in setting the lens parameters correctly and try to match the scale of the 3d models to that of the real world. Grab the camera and try to move it so that it is at the height of the real camera, and for the actual distance try to create some geometry that matches the dimensions of real objects. Then you might need to adjust the size of the camera to match the geometry to the objects in the scene. In other words you are up for a lot of work and lots of guessing. There are no automatic tools for accurate solving without proper depth estimation.

As an alternative, try using single image in fspy and determine the camera lens, height and scale there, and use those parameters for the tracked camera.

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  • $\begingroup$ Thank you for the answer, it is basically what I suspected (but I wasn’t sure since I never did this before). I will look into fSpy, maybe that helps. I noticed there are no distortion coeficients there, does that mean I should than use the refine for K1, K2 when solving? One more thing, I was thinking about figuring the camera movement manually, since it is only 90something frames (plus video is low quality so slight difference might not be noticeable). Is there a common practice/process I could follow? $\endgroup$ – davidv Sep 30 at 8:49
  • $\begingroup$ The camera movement is already solved accurately. , what is not is working is the scale and placement on the 3d world. You won't be able to determine distortion coefficients or refined focal length from this shot. If your goal is to learn how to do motion tracking use another shot in which the camera has displacement. $\endgroup$ – susu Sep 30 at 9:01

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