Re: Rotation matrix definition

[Carlo de Falco]

Il 26 nov 2019 17:39, Carlo de Falco <address@hidden> ha scritto:

Vecrot is for rotation vectrans for displacement vecscale is for scaling etc. All produce matrices as output. Composition of transformations corresponds to multiplication of matrices.

 If you really need to do anything more than a one-off computation with this stuff, I strongly recommend that you either read more on the theory of general affine transformations or you hire someone with more experience to write a code with a higher level interface to solve your problem.

c.

Il 26 nov 2019 17:18, Farzad Torabi <address@hidden> ha scritto:

Thank you very much dear Carlo 

Something changed, first it was vecrot, now vectrans? What's the difference? 

I also tried using 3 points to find the new coordinates and calculate the transformation matrix using quaternions, the results was different from vecrot. How's that? 

Also : in robatic books, there's one matrix for rotation and one for translation that get multiplied in each other, but I don't know if they are for the coordinate system or for the movements in space 

Farzad Torabi
Master in mechanical engineering

Il mar 26 nov 2019, 12:40 <address@hidden> ha scritto:

Il giorno 26 nov 2019, alle ore 11:56, Farzad Torabi <address@hidden> ha scritto:

dear Carlo

thank you for your great answer !

So the " T " is the transformation matrice to use, but can the "T" be used to either transform points coordinates or rotations or displacements ?

Yes, 

if T is 4x4 it can represent any affine transformation, i.e. scaling, rotation, displacement, etc.

If you want to understand theory about how this works (and I think you should), 

you will have to read about homogeneous coordinates and projective geometry, 

wikipedia has very good articles about those topics.

In practical terms, though, you should  just know that you can produce the transformation

matrix for a rotation and a displacement as 

  T = vectrans (displacement) * vecrot (rotation_angle, axis_direction)

c.