It appears that when I attempt to use vtkCellLocator with cells of type vtkLagrangeHexehdron, the cell locator sets the closest point out parameter to be the same as the original query point. It also does not show an error of any type, which is what I would expect if it had not been implemented yet. It does appear that the closest point distance and cell ID are being set, so it seems that some of the right things are going on. Is this a bug? Thank you!
Non-linear cells are not used very commonly, so it may be possible that implementation is indeed incomplete or even incorrect.
If you don’t get more specific response than this then you may follow these steps: Check out if there is a VTK test that checks vtkCellLocator behavior with vtkLagrangeHexahedron cells. If there is no existing test, then create one and send a merge request. If you also have suggestions how to fix/complete the implementation then include that in the merge request, too.