Camera projection matrix: why transpose rotation matrix?

Question

In the following:

http://cvlab.epfl.ch/files/content/sites/cvlab2/files/data/strechamvs/rathaus.tar.gz

there's a README file that says:

a 3D point X will be projected into the images in the usual way:
x = K[R^T|-R^T t]X

I remember that 3D to 2D Camera Projection Matrix requires the R rotation, not the transpose R matrix, i.e. I expect:

 x = K[R|-R t]X

Why does it say R^T and not simply R ?

Answer 1

It depends in which direction R was determined. I.e. is it a transformation of the camera in the global reference frame, or is it a transformation of the points in the local camera's reference frame.

The true answer is: Don't worry just check that what you've got is right.