[eigen] More efficient way to transform 3D coordinates to 2D.

[Billy Araujo <billyaraujo@xxxxxxxxx>]

I was thinking of implementing 3D to 2D transformation in the following way:

If I have 3 vertices, calculate v1, v2 vectors. Calculate cross
product of v1, v2 to get vz.
Then calculate vy using v1 and vz. vx = v1.

Then build a matrix with [vx, vy, vz] and multiply each vertex to get
local coordinates. The idea is to get 0 in z-coordinate.

Is there a better a better way to do this? Since I don't know anything
about eigen's geometry module.

Thanks in advance,

Billy.