Python API: gmsh.model.mesh.getNodes() returns empty lists for some surfaces of the model.
I am using Gmsh 4.9.5 on Windows. I am trying to follow the python tutorial x5.py to calculate normal and display them with arrows (as in the x5.py). For my model, this code:
for e in gmsh.model.getEntities(2):
s = e[1]
tags, coord, param = gmsh.model.mesh.getNodes(2, s, True)
Gets all model surfaces and for some surfaces, the gmsh.model.mesh.getNodes()
returns empty lists. This result seems like no nodes exist for the surface, which is obviously not the case.
I have included a screenshot of the outcome when the issue happens for the nodes of the two volumes (8 node hexahedrons) in blue, on the right side - notice missing green arrows for normals on all the nodes of the two volumes.