Why does Mesh Generator sometimes fail to interpolate values into an area with quadrangular elements?

This could be due to the presence somewhere in the domain of a polygon marker that is not related to a closed polygon. This has been seen to occur in large complex setups. You then have to find and delete the redundant polygon marker for the interpolation to work.
Fig. 1 illustrates an example of such an extra marker located outside a closed polygon. It may be difficult to detect without zooming into the local area.

TRICK: Open the mdf-file in an ASCII editor and look for lines ending with ' 0' in the [POLYGONS] section. These lines indicate the position of polygon markers with no arcs attached.

Fig. 1 - Example of polygon marker without related closed polygon 


Manuals and User Guides
Mesh Generator User Guide (p. 137 - 232)
Bathymetry Editor and Mesh Generator, Scientific Documentation