Homography on 90deg rotated projectors

something I ve been dealing with for ages and never really found out a solution, how do you setup homography with a projector rotated of 90 degrees ?

one sollution: shift the original points by one corner to the left or to the right

I just rotate the desktop in windows… then the renderer in vvvv does not need to be rotated.

genius! cool solution.

nice idea Sunep, but I am using the homography after the projector node to do a last fine tweak, so I rotate the projector on the input transform pin of the projector node, i d like to keep it this way for a more consistent workflow.

@ggml: i tried that but if you do it aftear a multiscreen or spatial edge blend module it doesn not work as it rotates the blending edge.


this could be one approach

RotatedHomography.v4p (12.0 kB)

@Sunep that won t work cause I need to rotate the projector on the Projector node.

you can multiply the homography and the perspective transform with Multiply (Transform). Changing the order should do the trick.

@velcrome, that s what I am doing right now, I expected that shifting the spreads of the original point or of the homography would do, but it doesn t, the whole render gets rotated and the point you picks are always the same…

you could alter the projecter node to have a more flexible aspect ratio than just a choice between 4:3 and 16:9 and then set it to the opposite of what it is normally and then just make vertical shift into horizontal shift and then rotate the desktop. Wouldn’t that work?

Not sure about all of the above, currently I have 4 projectors rotated of 90 degrees, connected with 2 Matrox over 2 outputs, with the spatial edge blend node, ideally I d like to keep the projector node configuration as it is, I understand that what you propose is a workaround more than a solution (consider for example that each couple of the projectors going to a Matrox are rotated each on a different direction, could be easily fixed, yes). It should work though.
Still I am interested to understand how to keep the patch consistent with the scene and modify the Homography accordingly.