Problem with Pattern Matching

[markus_71]

Hello,

some help with the following application is needed:

I have a litte robotics demonstration using a Mindstorms robot carring a USB Camera. The robot is controlled via bluetooth and the images are
captured via IMAQ USB - hardware setup works quite fine !

I need the robot to detect a target, which is a pattern very easy to recognize. A black X printed on a white sheet of paper (Lines are about 1cm thick,
X is about 12cm in diameter).

So I use a geometric pattern match (after some preprocessing) to recognize the X, this in general works, but I get only matches if I a allow a very
high "Obscured" value (about 60) and a match is only detected, if the image is in rectangular position to the camera (due to geometric distortion,
I think).
This is not useful for my application, because the robot should "see" the X, even if it looks on it with an angle of 45deg.

How could this be improved ?
I played around with some other pattern matching algos, but the geometric one seems the best for this
application.

Any help would be appreciated,
thanks in advance,

Markus

[BruceAmmons]

Markus,

Perhaps you could search for the individual lines of the X instead of the combined pattern.  You will get a lot more matches, but you should be able to sort through them to identify which ones intersect at the appropriate point.  This eliminates the distortion problem at the intersection of the lines.

Bruce