I also have some Python code for converting polygons from a watersheds shapefile into the UGRID format (
https://github.com/ugrid-conventions/ugrid-conventions/blob/v0.9.0/ugrid-conventions.md#2d-flexible-mesh-mixed-triangles-quadrilaterals-etc-topology). The major limitation here is that UGRID expects no gaps between the "faces" which limits its ability to store multi-geometries (i.e. Hawaii).
It also expects each "face" to have the same number of vertices, more or less.But it's a good idea to leverage that -- let's keep things as consistent as possible.
I wouldn't say that we expect every "face" to have about the same number of vertices, but indeed the use of fill values can blow up your data set if you have may tiny polygons and a few huge polygons. HDF5/NetCDF4 can help to reduce the problem on disk, but you may have a temporary memory issue. We used the fill approach because it seemed most consistent with the CF bounds polygons at the time. I don't know how different the ragged approach actually is. If you read and write multiple polygon, you may still have the same issues. The linearly indexed example that you gave:
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#Example%20H.2.4.1
would map to an efficient storage in memory as well, so that looks pretty attractive to me. Maybe we could also consider it as an alternative for UGRID storage.
I wouldn't go for the boundary_node_connectivity since those were introduced to specifically refer to boundaries. I would consider using the edge_node_connectivity. However, before anything else I would check with Ben Domenico and Stefano Nativi since they (and possibly others) have been looking at mapping OGC and netCDF data models. I guess that this question should have come up in that context.
Best<mailto:Chris.Barker at noaa.gov> regards,
Bert
DISCLAIMER: This message is intended exclusively for the addressee(s) and may contain confidential and privileged information. If you are not the intended recipient please notify the sender immediately and destroy this message. Unauthorized use, disclosure or copying of this message is strictly prohibited. The foundation 'Stichting Deltares', which has its seat at Delft, The Netherlands, Commercial Registration Number 41146461, is not liable in any way whatsoever for consequences and/or damages resulting from the improper, incomplete and untimely dispatch, receipt and/or content of this e-mail.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20140922/7a9dd29e/attachment.html>
Received on Mon Sep 22 2014 - 11:11:46 BST
