Add sinusoidal projection

[etourigny]

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.

[jonathan]

I support this proposal. (I am not an expert on this, but I do think it is important to make sure CF supports all the useful grid mappings.) Thanks. Jonathan

[jonathan]

It would be useful if anyone else who uses the sinusoidal projection could add their support to this ticket ​https://cf-pcmdi.llnl.gov./77. Thanks. Jonathan

[caron]

Is it possible to get a sample netcdf file with (preferably real) data that uses this projection?

[etourigny]

I'm not sure this is what you're looking for, but here is a sample file (from MODIS MOD09 surface reflectance data) that was converted from hdf to netcdf and reduced, using gdal:

gdal_translate -of netcdf -projwin -6985306.55659 -589994.90259 -6963245.33155 -606406.301703 HDF4_EOS:EOS_GRID:"/data/research/work/modis/mod09/orig/MOD09GA.A2010278.h11v09.005.2010280102154.hdf":MODIS_Grid_500m_2D:sur_refl_b01_1 tmp2-sin.nc
gdalwarp -t_srs EPSG:4632 -of netcdf tmp2-sin.nc tmp2-geog.nc

tmp2-sin.nc is the file with sinusoidal projection and tmp2geog.nc is the equivalent with a lat/lon geographic CRS.

Here is the relevant CF metadata of the sinusoidal file:

	short Band1(y, x) ;
		Band1:long_name = "GDAL Band Number 1" ;
		Band1:_FillValue = -28672s ;
		Band1:grid_mapping = "sinusoidal" ;
	char sinusoidal ;
		sinusoidal:grid_mapping_name = "sinusoidal" ;
		sinusoidal:false_easting = 0. ;
		sinusoidal:false_northing = 0. ;
		sinusoidal:longitude_of_central_meridian = 0. ;
		sinusoidal:longitude_of_prime_meridian = 0. ;
		sinusoidal:semi_major_axis = 6371007.181 ;
		sinusoidal:inverse_flattening = 0. ;
	double x(x) ;
		x:standard_name = "projection_x_coordinate" ;
		x:long_name = "x coordinate of projection" ;
		x:units = "m" ;
	double y(y) ;
		y:standard_name = "projection_y_coordinate" ;
		y:long_name = "y coordinate of projection" ;
		y:units = "m" ;

Unfortunately I don't think that any data provider distributes data with this projection as netcdf files. Modis data is distributed as HDF4 files.

[etourigny]

gtiff version of the same file

[etourigny]

and here is the WKT for the tmp2-sin.nc file

PROJCS["unnamed",
    GEOGCS["Unknown datum based upon the custom spheroid",
        DATUM["Not specified (based on custom spheroid)",
            SPHEROID["Custom spheroid",6371007.181,0]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433]],
    PROJECTION["Sinusoidal"],
    PARAMETER["longitude_of_center",0],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["Meter",1]]

[caron]

Seems ok to me.

[markh]

I support this change, it looks to be additive, and adding value.

The definition of the sinusoidal projection looks correct to me.

[jonathan]

Thanks to all for contributions and support. This proposal now meets the requirements to be accepted, if there are no objections or amendments in the next three weeks.

Jonathan

[mggrant]

Slightly belated, but this projection is one of those selected by the ​ESA Climate Change Initiative, which will be reanalysing the MERIS, MODIS and SeaWiFS time series and producing netcdf CF files. Certainly the ocean colour and sea surface will be using this projection and it would be very nice if it was formally supported. Currently, we're following the same convention as the MODIS HDFs.

[etourigny]

mggrant - do you see anything that should be added to or amended in the definition as it is?

[jonathan]

As enough support has been expressed and no further comments made, this proposal is accepted according to the rules. The change should be made in the next version of the CF standard document, as it appears in the original proposal, and Etienne Tourigny should be added to the list of additional authors of the convention. No change is needed in the conformance document.

Jonathan