Difference between SPATIAL_POSITION, MESH_NODE_POSITIONS and coord

[zahur.ullah1]

What is the difference between  SPATIAL_POSITION, MESH_NODE_POSITIONS and coords in the context of large deformation? 

And then how to calculate DISPLACEMENT from these fields?

[Lukasz Kaczmraczyk]

Zahur,

- Each node in MoAB mesh has coordinates. It consist initial geometry created in pre-processor and used by all MoAB functions.

- Sometimes we like to distinguish between geometry on mesh and reference geometry, to that we using MESH_NODE_POSITIONS, which are given as a MoFEM field. That allows to store higher order geometry with smooth surfaces. 

- If  MESH_NODE_POSITIONS is present, reference configuration is given by this field otherwise coords on MoAB entities are used.

- SPATIAL_POSITION field is usually used to describe current configuration.

In principle you can attach any name to field describing current and reference configuration. MESH_NODE_POSITIONS is not the best name, and in future we should name that field MATERIAL_POISTIONS.

In preview to see results correctly, you need to calculate 
1) W = MESH_NODE_POSITIONS-coords 

2) Wrap By Vector using W

3) U = SPATIAL_POSITION-MESH_NODE_POSITIONS

4) Wrap By Vector using U