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Simple Matrix Calc Issue

3 REPLIES 3
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Message 1 of 4
mitch.s
202 Views, 3 Replies

Simple Matrix Calc Issue

I have issues performing simple matrix calculations.

I need to convert a world space transform to a local transform.
So the equation is fairly simple :
Loc_Mtx = World_Mtx x Parent_World_INV_Mtx

I isolated the problem into the simplest possible graphs.
Using Maya nodes, everything works as expected. The Target and Result transforms correspond 1 on 1.
(note that the bogus grps are translated and rotated randomly (not scaled for test purposed))
Capture.PNG


I'm trying to do exactly the same thing in Bifrost (rotation order is default XYZ for everything)
It 'should be quite trivial, but the Result does not correspond to the Target... ???
Capture1.PNG

Does anyone have a solution for this simple matrix calc problem?

FYI

I'm in Maya 2024 / BIF 2.7.1.1

3 REPLIES 3
Message 2 of 4
Grahame_Fuller
in reply to: mitch.s

Have you tried reversing the order of matrix multiplication? Maya uses row vectors, but Bifrost uses column vectors. Matrices get converted (i.e. transposed) automatically going in and out of the graph, but for multiplication in the graph the transform that is applied "first" goes on the right (bottom input of the matrix_multiply node), i.e. Translate x Rotate x Scale in Bifrost is equivalent to Scale x Rotate x Translate in Maya.

 

It's a common issue when adapting transformations between different systems or from different textbooks.

 

I hope that helps,

gray


Grahame Fuller
Learning Content Developer
Message 3 of 4
mitch.s
in reply to: Grahame_Fuller

Thanks a lot... this works indeed!
But, holy guacamole, what a mindf#!%.

Message 4 of 4
Christoph_Schaedl
in reply to: mitch.s

This might help.

https://forums.autodesk.com/t5/bifrost-forum/matrices-in-maya-explained/m-p/9789311#M3218

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