more robust reading of DFM grids

Author: gei-rusty

stompy/grid/multi_ugrid.py

@@ -394,6 +394,7 @@ def __init__(self,paths,cleanup_dfm='auto',xr_kwargs={},grid=None,
                     if f in g.cells.dtype.names:
                         log.warning("Dropping extra cell field %s to avoid max_sides issues"%f)
                         g.delete_cell_field(f)
+                g.edge_to_cells(recalc=True) # 20250813: failing to merge, seems to be edge ordering. 
         if is_dfm:
             # kludge DFM output (ver. 2021.03) has nNetElem and nFlowElem, which appear to
             # both be for the cell dimension

stompy/grid/unstructured_grid.py

@@ -865,12 +865,14 @@ def process_as_index(varname):
         if 'face_edge_connectivity' in mesh.attrs:
             v=mesh.attrs['face_edge_connectivity']
             if v in nc:
+                start_index=nc[v].attrs.get('start_index',0)
                 # Some files advertise variable they don't have. Trust no one.
-                ug.cells['edges'] = nc[v].values
+                ug.cells['edges'] = nc[v].values - start_index
         if 'edge_face_connectivity' in mesh.attrs:
             v=mesh.attrs['edge_face_connectivity']
             if v in nc:
-                cells = nc[v].values
+                start_index=nc[v].attrs.get('start_index',0)
+                cells = nc[v].values - start_index
                 ug.edges['cells'] = np.where( np.isfinite(cells), cells, -1)
 
         if dialect=='fishptm':