In Houdini 20, to export the primvars:st:indices.
- Go to USD Exporter (tab Configure) or add a USD Configure above the USD Exporter.
- Go to section Import Data
- Check the box in front of the line Indexed Attributed
- Select or enter uv (they should be stored in the vertex attributes)
As you can see in the bottom of the USD Exporter, Houdini transfers automaticaly the UV attribute to ST attribute. The UV indices will follow during the export and the primvars:st primvars:st:indices will be exported in the USD file.
If you have any doubt:
- open a console command in C:\Program Files\Side Effects Software\Houdini 20.x.yyy\bin
- open your usd file with usdview:
hython usdview C:\MyPath\MyFile.usd