NEW FEATURE: Visualization of UGRID elements defined on the nodes
Summary
Within the UGRID conventions it is possible to defined variables to live on the nodes, rather than the faces. Within psyplot, we do visualize them at the the moment, but silently this provides wrong results.
Reason
It should be possible to visualize these elements, too.
Detailed explanation
Within the get_cell_node_coord method of the UGRID decoder, we generate triangles using a delauney triangulation.
I think this is fine for now as we do not have generic methods to generate grids from the nodes. What grid is the best is a very scientific question and should rather be answered by a custom decoder class for the data.
None the less, the current implementation in psy-maps (and psy-simple) is wrong. In the _polycolor method, we say transformed, array=arr.ravel(). For variables on a node however, this does not generate correct results because the length of the array (which is the same as the number of nodes) is not the same as for transformed, which has the length of the number of triangles.
So array should actually be the mean of the nodes for each generated face element (i.e. for each generated triangle).
Examples
matplotlibs tripcolor method is doing exactly this: https://github.com/matplotlib/matplotlib/blob/e097bf4baf8f275fda91f224b537076caf17dd91/lib/matplotlib/tri/tripcolor.py#L108
ping @platipodium