MLI6.1 McalGrid Perspective

[inv...@spammer.com]

We are using Matrox MIL6.1 and want to get a rough calibration of a
camera. MIL's camera calibration documentation claims to be able to do
a fit to a simple perspective pinhole model. The calibration succeeds
but when we use McalInquire to examine any of the parameters such as
camera position or grid origin they are all at obviously null answers.
(For instance the camera is at 0,0,100 and the grid corner is reported
at 0,0,0)

Does anyone know if:
a) this function, McalGrid with M_PERSPECTIVE_TRANSFORMATION, really
works; and
b) if it is possible to get the estimated parameters about the camera
that it claims to compute?

Thanks!
Josh

[Matrox Imaging]

Josh,

You are incorrect about the MIL documentation, as well as the
capability of MIL's Calibration module. The function McalGrid() with
the M_PERSPECTIVE_TRANSFORMATION mode is NOT designed to compute the
parameters of the camera and return it to the user.

MIL's calibration module (Mcal...()) consists of a set of functions
that allow you to map pixel coordinates to real-world coordinates.
This mapping can be used to get results from other MIL modules in
real-world units. The mapping can also be used to physically correct
an image's distortions. By getting results in real-world units, you
automatically compensate for any distortions in an image. Therefore,
you can get accurate results despite an image's distortions.

Furthermore, the perspective transformation mode can compensate for
rotation, translation, scale, and perspective distortions. For such
distortions, the perspective transformation mode is accurate for
points inside and outside the working area. This mode cannot
compensate for non-linear distortions such as lens distortions. The
perspective transformation mode best fits a global perspective
transformation function to the set of image coordinates and their
real-world equivalents.

The calibration grid is what the calibration module actually use to
calibrate itself. It is defined by the user to define its world
coordinate system. Therefore if the user defines the grid corner to be
at 0, 0, 0, the calibration module would, of course, have no choice
but accept the coordinates. The camera position can be any arbitrary
point that moves with the camera (default to 0, 0, 100); it does not
have to be the actual camera position.

Contact your local Matrox Imaging Sales representative or Technical
Support representative about your setup.

http://www.matrox.com/imaging/support/contact_tech.cfm

Technical Marketing,
Matrox Imaging

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