I'd like to use the same affine matrix M on some individual (x,y) points as I use on images with cv2.warpAffine. It seems cv2.transform is the way to go . When I try send an Nx2 matrix of points I get negged (
src = np.array([
[x1,y1],[x2,y2],[x3,y3],[x4,y4]], dtype = "float32")
print('source shape '+str(src.shape))
dst=cv2.transform(src,M)
cv2.error: /home/jeremy/sw/opencv-3.1.0/modules/core/src/matmul.cpp:1947: error: (-215) scn == m.cols || scn + 1 == m.cols in function transform
I can get the transform I want just using numpy arithmetic :
dst = np.dot(src,M[:,0:2]) +M[:,2]
print('dest:{}'.format(dst))
But would like to understand whats going on . The docs say that cv2.transform wants a number of channels equal to number of columns in M but I'm not clear what the channels would be - maybe an 'x' channel and 'y' channel, but then would would the third be, and what would the different rows signify?