Dev:Source/Motion tracking/Shots catalog

Clips catalog

See http://download.blender.org/ftp/incoming/libmv.

If you have some stuff to upload usable with libmv just put it there! Thanks!

General requirements

Textures

The scenes should have good texture so that tracking is easy.

We can add challenging scenes later.

Scene

• Boxes with texture are good.
• Complicated objects like bushes or trees are bad.
• The scene must be static (no cars, people, birds, godzilla, etc).

Camera

Sensor Implications

• CMOS sensors are affected by Rolling shutter!! CCD based sensors, are not.
• CMOS rolling shutter artifacts can break 3D reconstruction from 2D tracking. The LibMv team is well aware of this phenomenon and will implement a correction scheme soon.
• For this reason, possibly please use a camera with a CCD based sensor.

Calibration

libmv calibration grid

Here's the procedure to calibrate the camera.

Prepare the calibration grid

• Download this libmv calibration grid you see on the right.
• Affix it to a really flat object: something that has a bit of bend is unacceptable and will give poor results.

Shoot it

• The checkerboard and camera should be still.
• Take several views of the calibration target at different angles (or a video in HD).
• The perspective on the checkerboard should be very apparent (in addition to front-on views).
• Each shot of the checkerboard should try to cover as much of the field of view of the camera as possible, while still showing the full checker board (important for distortion correction).

Note This is important since the distortion tends to happen towards the edges of the view, so if the grid only occupies the middle 25% of the view it won't produce a good calibration. Even with the full autotracking that you get in the commercial packages, you can get superior results if you properly calibrate your camera; especially for difficult shots where there is ambiguity, etc.

Calibrate the lens

Run one of the calibration tools, to find the lens intrinsic parameters:

• focal length x
• focal length y
• principal point x (center of projection)
• principal point y
• skew
• radial distortion coefficients (typically ~1-5 numbers) which describe:
  • barrel
  • pincushion
  • tangential distortion

Types of required camera movement

Type of movement	Description
Moving and rotating camera	Camera is not always pointing at one part of the scene.
Panning shots	Camera on a tripod, rotating around a fixed point (if possible the camera's "Nodal point", but you need a special tripod for that)
Sideways tracking shots	Walking sideways keeping the camera pointed forward (e.g. not circling). Hand-held wobbling is ok
Pull-in tracking shots	Walking towards the scene. Hand-held wobbling is ok
General motion with planar scene	Example: camera keeps a big billboard in view and only the billboard
Target tracking	Circle strafing around an object: camera points on one part of the scene (intersecting principal ray)