Elements attached to ghost nodes after .stp import from Catia
Hello,
I am currently working on a .gmsh converter to Exodus II format (https://github.com/diehlpk/gmsh-exodus-converter).
After opening a ".stp" 3d parts (a cube for example) to Gmsh, I perform a simple 3D mesh by clicking on Mesh > 3D, then Save. I then realized that some Elements were attached to the node number 0. However, when checking the nodes, it appeared that there is no node number 0.
In the nodes section, it is possible to see that the first node's number is 1 (not 0): $Nodes 429 1 0 0 0 2 0 10 0 3 -10 0 0 4 -10 10 0 5 -10 0 10 6 -10 10 10 ...
When I check the elements, I have Elements attached to the zero, which seems impossible, since there is no node number 0: $Elements 2335 1 15 2 0 1 1 2 15 2 0 2 2 3 15 2 0 3 3 4 15 2 0 4 4 5 15 2 0 5 5 6 15 2 0 6 6 7 15 2 0 7 7 8 15 2 0 8 8 9 1 2 0 1 1 9 ...
This is critical to the code I am working on since it will mainly be used to import CAD files from Catia. Could you please help me understand how the Elements attached to the (seemingly) non-existing 0 node work?
Thank you, ilyass