I have a converter that is generating USD files from scientific data sets. Most of these are 3D meshes with interior polygons carrying dozens of data values translated to USD primvars. I want to clip the data and create a “cap” or patch over the clip to show the interior. It appears to me as if Houdini is interpolating the values incorrectly (the interpolation is per-vertex in USD).

In the attached images and hip, the data is the distance squared from the origin.



The above shows the data values when clipped



Intersecting the data with a grid at the location of the clip gives the image above (the grid is offset from the cube to show the values). Notice the values do not match. One issue with using the boolean is that it results in non-manifold edges.

So (in the hip), I clip the data to a small value that doesn't produce non-manifold edges, and I still get similar results.

Any help is appreciated. The real data sets are significantly larger, so manual tweaking of the data or results is no allowed.

Mark

What's incorrect about it?
If you lerp P values to the same point as the clip, I get the same value for the attributes as the clip sop.

The values generated by the boolean are interpolated between the left and right inputs. Since the grid is missing these attributes, they are blended with zero.

Doh! Thanks, that makes sense now. I though it was interpolating between 0, but my frazzled brain couldn't quite pull it together.

Throwing an AtrribTransfer after the boolean gives me the answer I was looking for.