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Ticket Resolution Summary Owner Reporter
#92 fixed Add oblique mercator projection davidhassell mcginnis
Description

The Oblique Mercator projection is used by at least one regional climate model, RegCM3, which is part of the NARCCAP climate modeling program. Currently we record its map projection information using the transverse_mercator projection, which I have learned is very similar but not quite the same. I propose to add this map projection so we can get it right.

Proposed text:


Oblique Mercator

grid_mapping_name = oblique_mercator

Map parameters:

  • azimuth
  • latitude_of_projection_origin
  • longitude_of_projection_origin
  • scale_factor_at_projection_origin
  • false_easting
  • false_northing

Map coordinates:

The x (abscissa) and y (ordinate) rectangular coordinates are identified by the standard_name attribute value projection_x_coordinate and projection_y_coordinate respectively.

Notes:

Notes on using the PROJ.4 software package for computing the mapping may be found at http://www.remotesensing.org/geotiff/proj_list/hotine_oblique_mercator.html . The Rotated Mercator projection is an Oblique Mercator projection with azimuth = +90.


If adding a new attribute for azimuth is problematic, this proposal could be modified to add the rotated_mercator projection instead, which is a special case of Oblique Mercator with azimuth = 90.

Note that apparently there is a subtle technical difference between an Oblique Mercator projection and a Hotine Oblique Mercator projection that depends on when the rectification from skew grid to map grid is applied. Since most mapping packages don't support a rectified grid angle parameter at all (effectively giving it a default value of 90 degrees, such that it has no effect), to avoid unnecessary proliferation of attributes I propose to omit this parameter and elide this distinction until such time as it proves necessary.

My knowledge of this topic is quite limited; I have made this proposal based on what understanding I have gleaned from the geotiff website and communications with colleagues working with our RegCM3 output in GIS. Commentary from experts would be very welcome.

#77 fixed Add sinusoidal projection davidhassell etourigny
Description

The sinusoidal projection is used in NASA's MODIS products, and is supported by PROJ.4, Snyder and OGC WKT.

The mapping would be simple as this projection uses few existing CF projection parameters.

Proposed text :

====

Sinusoidal

grid_mapping_name = sinusoidal

Map parameters:

  • longitude_of_projection_origin
  • false_easting
  • false_northing

Map coordinates:

The x (abscissa) and y (ordinate) rectangular coordinates are identified by the standard_name attribute value projection_x_coordinate and projection_y_coordinate respectively.

Notes:

Notes on using the PROJ.4 software packages for computing the mapping may be found at http://www.remotesensing.org/geotiff/proj_list/sinusoidal.html. Detailed formulas can be found in [Snyder] pages 243-248.

#72 fixed Adding the geostationary projection. davidhassell martin.raspaud
Description

There seems to be a need from the weather satellite people to add the "geos" projection to the list of projections in the CF metadata.

"geos" stands for geostationary. The projection is described in detail in the "CGMS 03, LRIT/HRIT Global specification" (Eumetsat) document. (see here also: http://remotesensing.org/geotiff/proj_list/geos.html )

A possible text for this projection is:

Geostationary projection


grid_mapping_name = geos

Map parameters:

latitude_of_projection_origin

longitude_of_projection_origin

perspective_point_height

false_easting

false_northing

Map coordinates:

The x (abscissa) and y (ordinate) rectangular coordinates are

identified by the standard_name attribute value projection_x_coordinate and projection_y_coordinate respectively. Notes:

Notes on using the PROJ.4 software packages for computing the

mapping may be found at http://www.remotesensing.org/geotiff/proj_list/geos.html . These notes assume the point of observation is directly over the equator. The projection coordinates in this projection are directly related to the scanning angle of the satellite instrument.

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