# how can I reproject points once I have the homography matrix?

Hi all! I have calculated a homography matrix using cvFindHomography() and now I would like to use this matrix to do some point reprojection.

originally, i thought I could simply do

p' = H * p, where H my is my obtained (3x3) homography matrix, p is my original point a Vec3f point (with z=0) p' is my reprojected point (again Vec3f).

apparently the compiler whines though that the "*" operator has not been defined for such multiplication.

What could be wrong? I am using the operator "*" in some wrong way?

thank you for your help.

While not completely sure what you are trying to do, and what the rest of your code looks like, have you employed perspectiveTransform()? http://docs.opencv.org/2.4.8/modules/core/doc/operations_on_arrays.html?highlight=perspectivetransform#void%20perspectiveTransform%28InputArray%20src,%20OutputArray%20dst,%20InputArray%20m%29