Tagging Surfaces in .vtu files

Our code writes out XML VTK unstructured grid files, which are then visualised in ParaView. Currently, however, information about boundaries is lost during the export process (as we just write out volume cells) and has to be recovered through clipping and surface extraction filters.

To this end, I was wondering if there is any means of tagging certain points in the VTU file as belonging to a named entity? In ParaView a user could then ask for all faces which are made up of these points, thus making it trivial to extract surfaces.

Regards, Freddie.

You can have a PointData array, where the value is an id of the face the point belongs to.
Then, in ParaView, you can use Threshold to extract points and thus one surface.

Is it possible to have Threshold just extract the faces on the relevant cells as opposed to the cells themselves? In our export (VTU writing) code, we already strip away all cells not on a boundary. What we are looking to simplify is surface extraction.

Additionally, is it possible to associate categorical names with threshold values? This would make it easier for our users to know what to dial in/select.

Regards, Freddie.

No, you may need to use Extract Surface filter then.

Yes but it is less handy. You should use string values. Then the Threshold won’t work so you have to make a selection query through Find Data and then Extract Selection.

But from what I see, you may want to modify your code to export MultiBlock data set, with one block per faces and one block for the inner volume. Then extraction is much easier