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Ticket Resolution Summary Owner Reporter
#6 wontfix Unstructured Grids Vocabulary Request cf-wg-supporting-technologies@… tomgross

Welcome to the Unstructured Grid Mailing lists. This task will be a sort of test for our ability to use the new CF task tracking and mailing list methods. Remember: Don't "reply" to the emails directly, use the web page instead. See GettingStarted and UnstructuredTaskLists

This first task/discussion thread concerns the creation of a vocabulary for Unstructured Grids. We began the task at the workshop and agreed upon a few useful starting points, such as the use of "Unstructured Grids" rather than "Unstructured Meshes", and the use of "Cell" instead of "Element" to refer to that fine grain structure which is usually a triangle or quadralateral made up of nodes, edges and faces.

Contribute to this thread your ideas for other necessary vocabulary and perhaps other structures and "things" we need to describe in the construction of the Unstructured Grid Data Model

Tom Gross

#7 wontfix Unstructured Grids SuperGrid Requirements cf-wg-supporting-technologies@… tomgross

The irregular grid specifications have brought up several spatial objects which are not precisely described by a single coordinate location. For instance the edge of a triangle, or the triangle itself. An edge must be described by two points and the triangle by three points. A variable such as heat flux or area are not, necessarily, located at a single point. For convenience we could define spatial locations, center of edge or center of triangle, which could serve as coordinate locations for these variables. As it will still be necessary to describe the edge or triangle, by calling out the locations of the vertices, these derived locations are redundant. These extra locations are very much like the gridspec supergrid points (Balaji 2006). They might be useful enough to become a requirement of the CF conventions.

Should there be a requirement for the inclusion of these auxiliary locations for the center points of higher dimensional objects, such as line segments or areas?

#9 wontfix Extensions to CF grid mapping attributes to support coordinate reference system properties cf-conventions@… pbentley

1. Title

Proposed Extensions to CF Grid Mapping Attributes to support CRS Properties

2. Moderator

Jonathan Gregory

3. Requirement

Previous posts to the CF mailing list have identified the requirement for additional attributes that could be used to provide a fuller definition of the characteristics of the coordinate reference system (CRS) used by spatial coordinates within a netCDF file. This proposal attempts to define attributes for several commonly used CRS properties.

4. Initial Statement of Technical Proposal

Owing to the length of this proposal, the full specification text is included in the attached PDF document.

(NB: If it is considered more convenient, e.g. for discussion purposes, to upload the full text of this proposal into this Trac ticket, then the author is happy to do so.)

5. Benefits

Scope: potentially all producers and end-users of netCDF datasets could exploit the proposed new attributes.

New capabilities: the proposed new attributes would enable data producers to more accurately record the specific characteristics of the coordinate reference system (or systems) used to define spatial coordinates within netCDF files.

Example use-case 1: A data producer has collected meteorological observations using a sensor platform which uses, for example, a particular geodetic datum (e.g. WGS 84, NAD 83, OSGB 36) to record spatial coordinates. It is desirable for this piece of CRS metadata, and others like it, to be recorded in appropriate netCDF CF attributes.

Example use-case 2: A climate data center wishes to convert a legacy dataset to netCDF format and make it available over the internet. The legacy dataset is based upon an unusual or customised coordinate reference system (e.g. transverse mercator projection using, say, the Clarke 1880 ellipsoid). As before, these CRS details need to be encoded in agreed, standardised CF attributes.

6. Status Quo

The author is not aware of alternative CF attributes or mechanisms that could be used to encode the desired additional CRS properties.

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