Need to generate tform matrix from triangle parameters.

If a user draws a triangle with parameters b, h and theta and wants to change an entire image via a transformation from a new triangle with user inputed parameters b', h', theta'. How can the transformation matrix be found?

Answer 1

[Matt J]

The corners of each triangle are separated by vectors dy and dx. There is some 2x2 matrix A which transforms them from triangle 1 to triangle 2,

dy2=A*dy1
dx2=A*dx1

These are linear equations in the unknown A, which you can solve.

[Marshall]

Does this transformation also include a change in angle?

[Matt J]

yes, the angle between dy2,dx2 can be different from dy1,dx1, as long as both are significantly non-zero.

[Marshall]

And can this matrix then be applied to the rest of the image?

[Matt J]

would it be possible to use your absor function for this vary problem?

Only if theta doesn't transform. Otherwise, the transformation is not a pure rotation.

[Marshall]

Matt J I have since managed to solve for the matrix A how can then use this matrix to generate a matrix for an image?

Answer 2

[Matt J]

Why not use fitgeotrans, like you were advised here?

[Marshall]

I don't have the version of matlabwith fitgeotrans. I need to find someway without using two images.