Hi All-

Is it possible to make a transform SOP “look at” another object at the SOP level? Easy to do with a geo @ the OBJ level, but I need it at the SOP level.

Any ideas?

-jon

Append a default Transform SOP. In the RX, RY, RZ parameters put in the following expressions:
explodematrix(dihedral(vector3(0,0,-1),vtorigin(“..”,“lookat_path”)), “SRT”, “XYZ”, “RX”)
explodematrix(dihedral(vector3(0,0,-1),vtorigin(“..”,“lookat_path”)), “SRT”, “XYZ”, “RY”)
explodematrix(dihedral(vector3(0,0,-1),vtorigin(“..”,“lookat_path”)), “SRT”, “XYZ”, “RZ”)


Substitute lookat_path with the path to the object you want to look at. You can substitute vector3(0,0,-1) with the axis that you want to align with. I picked the negative Z axis here because that's what the object-level does. Notice that “SRT” is the transform order which should match the transform order of your Transform SOP. Ditto for “XYZ” as the rotation order.

is there an equivalent of the dihedral
function in vops?

-cpb

Align VOP

Thanks for the explodematrix code edward.
I tried this in a copy SOP, where I was copying a bunch of disks to points, where I wanted the disks to be perpenticular to world zero.
It works!
Much thanks
-syntheticperson

cpb
is there an equivalent of the dihedral
function in vops?…

well, there is directly Look At VOP which will compute rotation matrix from given direction and up vector

be aware of Align VOP and dihedral functions for this as they don't care about up vector and therefore you may be experiencing flipping

I found this old thing I apparently made long ago. I think it still probably works…

Graham,

I tried your SOP/lookat, but it does not show up in houdini 12.1.177.
Have you tried it in houdini 12.1.177?

thanks

-syntheticperson

I'm assuming you mean 12.1.77, the latest production build, but yes, I see it. Assuming you've got it loaded, it should show up in the tab menu with the name “Geometry Lookat”.