[CF-metadata] FGDC projection parameters not well documented

From: John Caron <caron>
Date: Wed, 04 Oct 2006 13:43:39 -0600

I know that we decided to use FGDC names for projection parameters, but there doesnt seem to be any further documentation or references in the FGDC-STD-001-1998 doc to explain them.

For example:

Polar stereographic

Map parameters:

    * straight_vertical_longitude_from_pole
    * latitude_of_projection_origin - Either +90. or -90.
    * Either standard_parallel or scale_factor_at_projection_origin
    * false_easting
    * false_northing


The first parameter doesnt exactly match any proj4 names:

Name Polar Stereographic

Projection Parameters

Latitude of natural origin 1 NatOriginLat latitude_of_origin Angular
Longitude of natural origin 2 StraightVertPoleLong central_meridian Angular
Scale factor at natural origin 5 ScaleAtNatOrigin scale_factor Unitless Not in original GeoTIFF ... I added for similarity with EPSG. Defaults to 1.0.
False Easting 6 FalseEasting false_easting Linear
False Northing 7 FalseNorthing false_northing Linear


I would assume "straight_vertical_longitude_from_pole" = "Longitude of natural origin" but the FGDC name seems poorly chosen, whats a "vertical longitude?"

Also, one must choose "standard_parallel" or "scale_factor_at_projection_origin". I would assume that one finds the scale factor that makes the distortion at the standard_parallel = 1.0, but theres no docs that would explain that. Someone else might make a different assumption.

Im thinking we need to start annotating the CF spec, unless someone knows where FGDC has documented all of this.
Received on Wed Oct 04 2006 - 13:43:39 BST