利用者:Ccherrett/ReconstructionAndMotionTracking competition
June 04, 2007
Determining the ground plane:
It would be nice to see the Blender tracker allow you to align the camera and objects to the Blender grid system. This would help when building your geometry into the scene after the track. In programs such as voodoo it imports the camera and point cloud but it is not aligned to the grid system. It would be nice to almost be able to optionally define your ground plane and align to it.
I found this tutorial on PFTrack. It has a fantastic way of determining the ground plane:
http://www.cmivfx.com/m/c4d_pftrack4.mov
Film Back:
I must admit that I do not understand fully why film back is necessary but apparently it plays some role in obtaining a good motion track. I have been hunting for some indication of what exactly the film back is and I found the following article to have a paragraph that might shed some light on it:
<quote from http://www.fxguide.com/article212.html>
Many operators fear trying to solve a 3D camera move that has had a static resize in telecine. While a wider or larger picture will perhaps allow tracking markers to be valid longer before moving off screen, static resizes in telecine are not as disastrous as sometimes thought. Hill explains that while an accurate film back is important, it is not "as important as the pixel aspect ratio. If you get the filmback wrong then you're going to get an inaccurate focal length value, but this is rarely a major problem unless the value calculated is way out. Pixel aspect ratio, on the other hand, can kill a camera track. It acts like a kind of 1D lens distortion and will have a very big effect on tracking accuracy. If the telecine process puts any squeeze on the frames then you're in trouble". If the image is adjujsted in telecine, it is important to know where the principal point (the projection of the camera optical center on the film back) lies in the image. With cropped footage, "it can even lie outside of the image," jokes the RealViz team. "An error of a few pixels on the principal point will generally not affect the tracking too badly. Knowing the value of the camera focal length is helpful, both for accuracy and speed. Measurements on the set are also helpful. Any such measurement can be used by MatchMover to find a quicker and more accurate solution."
</quote from http://www.fxguide.com/article212.html>
The following is from the book "Matchmoving The Invisible Art of Camera Tracking" page #14
http://www.tsiwebdesign.com/testing/not_all_film_backs_same.jpg
The following is from the book "Matchmoving The Invisible Art of Camera Tracking" page #76
Screen Shot of MatchMover Pro 3.0
http://www.tsiwebdesign.com/testing/camera_parameters.jpg
The following is from the book "Matchmoving The Invisible Art of Camera Tracking" page #76
Screen Shot of Boujou
http://www.tsiwebdesign.com/testing/cameras_panel.jpg
Good explanation of converting film back between 3D Max and Maya
Here are some screenshots from other apps allowing you to define film back / film gate:
This is from Maya:
This is from Fusion:
http://www.vfxpedia.com/images/Camera3d_controls_perspective.jpg
This is from Voodoo Tracker:
http://www.tsiwebdesign.com/testing/voodoo_filmback1.png
http://www.tsiwebdesign.com/testing/voodoo_filmback2.png
