Rotated Grid Definition

Purpose

This CRS definition describes a rotated grid, specifically for the COSMO data set (rotation angles 40.0 and -170.0). It is encoded in GML as per OGC rules, with an identifying URL TBD that resolves to this GML.

Corresponding Discussion Issue.

Many thanks in particular to Martin Desruisseux, Even Rouault, and Roger Lott! -- PeterBaumann - 18 Apr 2021

Concept

A projection is defined, working title: Rotated_Latitude_Longitude. This is a member of a new (?) code list.

This projectioin has the following parameters:

• latitude_of_origin in degrees; IOGP URN: urn:ogc:def:parameter:EPSG::8801
• longitude_of_origin in degrees; IOGP URN: urn:ogc:def:parameter:EPSG::8802

(Edit by Martin on April 25): I took those parameters from the Mercator projection on the (wrong) assumption that the operation was some kind of projection. We probably need to define a new set of parameters. Taking OGC 18-010 §14.3.2 as a source, the parameters may be:

• "Latitude of rotated pole" in degrees. OGC URN: urn:ogc:def:parameter:OGC::to be determined
• "Longitude of rotated pole" in degrees. OGC URN: urn:ogc:def:parameter:OGC::to be determined
• "Axis rotation" in degrees. OGC URN: urn:ogc:def:parameter:OGC::to be determined

I'm not aware of IOGP codes for those parameters.

GML Definition

see attachment ...which is DRAFT - likely incomplete and incorrect!

(Edit by Martin on April 25): current draft is for a ProjectedCRS. It probably needs to be changed to a DerivedCRS.

WKT Definition

Discussion (thanks, Even!):

For now PROJ 7, will understand things like

+proj=ob_tran +o_proj=longlat +o_lat_p=52 +o_lon_p=-30 +lon_0=-25 +datum=WGS84 +no_defs +type=crs

and

GEOGCRS["WMO Atlantic Pole",
    BASEGEOGCRS["WGS 84",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]]],
    DERIVINGCONVERSION["unnamed",
        METHOD["PROJ ob_tran o_proj=longlat"],
        PARAMETER["o_lat_p",52,
            ANGLEUNIT["degree",0.0174532925199433]],
        PARAMETER["o_lon_p",-30,
            ANGLEUNIT["degree",0.0174532925199433]],
        PARAMETER["lon_0",-25,
            ANGLEUNIT["degree",0.0174532925199433]]],
    CS[ellipsoidal,2],
        AXIS["latitude",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["longitude",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]]]

Issues

Open

• cosmo.gml attached has dangling xlinks
• ellipsoid ok?
• establish codelist with OGC-NA

Closed

• Q: uom for angles?
  • A: uom for COSMO is degrees.