Orientation rot on Unreal Spline component HDA outputs

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Joined: March 2019
Howdy all,

I was wondering if anyone has had any luck with getting useful orientation or rotation information on Unreal spline outputs from HDAs, or can give any pointers.
I have a situation where I would like to output a unreal spline (in addition to an instancer or static mesh) that can be used by a Blueprint to do additional work natively in Unreal.

The end hope is being able to replicate the pitch, roll and yaw of the Houdini curve in Unreal, but I've have broken down the problem to the simplest test case you can see below.

Left is a HDA that outputs an instancer, placing @unreal_instance along a Houdini curve with a copy to points, and converts @N and @up to @orient before outputting. It also outputs this same curve, with renamed @orient to @rot, and a @scale attr (based on looking at how Houdini inputs UE splines ).

Right is a blueprint that reads a spline component and places instances at each point of the spline using Add Instance and the Get Transform at Spline Point nodes.

Expected different coordinate system aside, when there is no @rot attr present, the blueprint essentially works as if a native unreal spline was used, with each instance orientated to the next point on the spline.
When rot is present however, there is rotation information to be seen on the spline points but it's a bit nonsensical (random values in each channel, flipping sign from point-to-point). I can't work out how this should be interpreted into unreal - or even if it is meaningful/accurate. @scale works perfectly fine, so I'm inclined to think(hope) maybe the rotation information could be significant.

I think I'm pretty on top of the curve stuff in Houdini but am still only a few days into really diving deep into unreal splines so potentially I'm missing something on that end.

Edited by furlerer - June 11, 2022 21:43:38

hda_spline_ue_no_attrs.jpg (71.5 KB)
hda_spline_ue_rot_attr.jpg (81.8 KB)

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