Project tracker position back to screen fixing the distortion

Hi everyone! I am glad to be a part of OpenFrameworks community, hopefully outside the beginner forum soon.

I am working on a multimedia project where IR tracker position is scanned with a camera and projected back to the same screen with a projector.

The problem I face at the moment is that tracker position taken by camera have to be calibrated to fit the projection size and position. I was planning to use simple a map (horizontal and vertical) function to map tracked coordinates to screen coordinates, but this will give a good result only when a camera is located right in front of the screen.

When a camera is in offset horizontally or vertically - the tracker position will be a trapezoid (where ab != cd on camera tracked position I), but probably even worse where none of the sides are equal.

I want the tracking and projection be as precise as possible, so i am looking for a way to correctly map the tracker position to the projected screen position. I can take 4 positions of the tracker, which will represent points a,b,c,d on screen I, but I don’t know how to map them to points a,b,c,d on projected screen II.

There is a warpPerspective in OpenCV, which does similar operation to an image, so I need the same, but just to map the coordinates. There is probably an easy solution for this, I just don’t know how to correctly search for it :smile:

Well neverming. I think it’s called “quad warping”. Since I cannot delete the thread, I will post a solution that worked for me. Currently reading this thread:

ofxQuadWarp can also do quad warping with points, check out the example.

If you want even more precise mapping between the camera coordinate system and the projector coordinate system, you can do “camera projector calibration”, which, if I understand well, take care about the differences between the optics of the two devices.

Kj1: thanks a lot, this looks like the thing i was looking for. But as soon as you find the solution - you try to make it better, so I started to look for no OpenCV solution and luckily found it here:
Quad warping / homography without opencv (the source example by davidchatting).

I still don’t understand how everything works with matrixes but this example works exactly as i expected!

Great addon, cloned it for my future projects :slight_smile: