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SaKo
@sako.works

i've been trying to figure out the math for 4 point perspective transforms like this for years now... (on and off) the last time I looked into it, I got as far as (finally) learning matrices and dove deep into videos/lessons on linear algebra and perspective projection and homogeneous coordinates

SaKo
@sako.works

but I still don't know how to do these kinds of arbitrary 4 point transforms, which is the main thing I've been wanting to learn... were there any pages or resources that helped you to understand the math behind it?

torcado
@torcado.com

yep your intuition is correct, matrices and linear algebra! there's a lot of strange terms which makes learning annoying. 8dof/projective transform/homography all point to essentially the same concept. i used the matrix from this answer for my calculation math.stackexchange.com/questions/49...

math.stackexchange.comHow to compute homography matrix H from corresponding points (2d-2d planar Homography)I went through this thread Mapping Irregular Quadrilateral to a Rectangle If i know the 4 corresponding points in image say p1->p1' p2->p2' p3->p3' p4->p4' then how to compute pi(x,y) from pi'(x...

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torcado
@torcado.com

essentially, i generate a homography matrix from 4 points to 4 other points, and then i can multiply the inverse of this on any external set of 4 points to get to that shape's projection. and because this is projective, points scale closer to the horizon/etc.