I posted something a few days ago that used the lengths of the opposite vertical sides to locate the robot on the field. The math is pretty simple, basically doing the same thing as the white paper for the vertical sides of the rect, and ultimately constructing a non-right triangle. You could use the law of cosines if you wanted to identify the angles within the triangle. You can also base if off of angles, I'm sure, but I suspect that will be less accurate due to lens distortion and coarse resolution.
As mentioned in the other post, I highly encourage you to build a backboard, attach some large number tape measures to it, perhaps yard sticks, and take images from various locations on the field. Perhaps mark the floor with tape and label them (A, B, C, etc.) so that you know the measurements. Keep notes of distance to target, location, etc. Then use Vision Assistant to work through some of the images by hand using the techniques listed above or from the white paper, and see how close you get. Once you get the hang of it, write code that runs over the same images, then move to the locations on the field with the live camera and see how well it works.
Finally, consider what you are trying to locate. Is it the center of the hoop, the center of the rectangle, or what. Once you know where you are, you may need some more math to actually aim.
The post from the other day is here ..
http://www.chiefdelphi.com/forums/sh...5&postcount=18.
Greg McKaskle