[GRASSLIST:7939] Re: Problem using r.in.gdal to import geoTIFF of US NDVI

[Markus Neteler]

(cc bugtracker)

On Tue, Aug 16, 2005 at 03:39:45PM -0400, Kenneth Waight wrote:
> I'm using r.in.gdal to import a geoTIFF file of U.S. NDVI data.  The  
> import is performed, but this message is displayed and the data  
> doesn't seem to be projected correctly:
> 
> GRASS_INFO_WARNING(20541,1): Datum  
> 'Not_specified_based_on_Authalic_Sphere' not recognised by GRASS and  
> no parameters found. Datum transformation will not be possible using  
> this projection information.
> Over-riding projection check.
> Proceeding with import...
> 
> CREATING SUPPORT FILES FOR ndvi.2004113.test
> SETTING GREY COLOR TABLE FOR ndvi.2004113.test (8bit, full range)
> 
> 
> It's close but is a few km off when I reproject to a lat-lon grid.   
> Here's the dataset information:
> 
> http://glcf.umiacs.umd.edu/data/modis/ndvi/guide.shtml
> U.S.16 day Vegetation Index User Guide
> 
> * Projection: Alber's Equal Area Conic Conformal
> reprojected from native MODIS projection: Sinusoidal
> Central Meridian used was 96d W
> std Parallels of 29d 30' 0" and 45d 30' 0"
> Latitude of Origin is 0d 0' 0"
> Easting & Northing are 0.0000000000 m
> Datum: sphere (a sphere of radius 6370997 m)
> Resolution is 250 meters
> ***NOTE*** - When you load the geotiff, many programs may not  
> correctly recognize the datum and report a wrong datum (i.e., WGS  
> 1984). THE DATUM IS THE SPHERE USED IN MODIS DATA, WITH A RADIUS OF  
> 6370997 METERS!!!
> 
> 
> Any ideas?

I have downloaded such a file and tested with gdalinfo:

gdalinfo US.Albers.2005145.ndvi.tif
Driver: GTiff/GeoTIFF
Size is 21000, 13000
Coordinate System is:
PROJCS["unnamed",
    GEOGCS["Unknown datum based upon the Authalic Sphere",
        DATUM["Not_specified_based_on_Authalic_Sphere",
            SPHEROID["Sphere",6370997,0,
                AUTHORITY["EPSG","7035"]],
            AUTHORITY["EPSG","6035"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4035"]],
    PROJECTION["Albers_Conic_Equal_Area"],
    PARAMETER["standard_parallel_1",29.5],
    PARAMETER["standard_parallel_2",45.5],
    PARAMETER["latitude_of_center",0],
    PARAMETER["longitude_of_center",-96],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]]]
Origin = (-2356750.000000,5769500.000000)
Pixel Size = (250.00000000,-250.00000000)
Metadata:
  AREA_OR_POINT=Point
  TIFFTAG_SOFTWARE=hdf2geotiff v0.1.5
Corner Coordinates:
Upper Left  (-2356750.000, 5769500.000) (128d59'15.31"W, 49d50'21.28"N)
Lower Left  (-2356750.000, 2519500.000) (118d30'25.87"W, 21d47'47.16"N)
Upper Right ( 2893250.000, 5769500.000) ( 56d16'50.11"W, 48d 0'54.53"N)
Lower Right ( 2893250.000, 2519500.000) ( 68d37'26.12"W, 20d30'41.05"N)
Center      (  268250.000, 4144500.000) ( 92d52'8.97"W, 38d54'34.96"N)
Band 1 Block=21000x1 Type=Byte, ColorInterp=Gray

Actually I don't understand the phrase "THE DATUM IS THE SPHERE USED IN MODIS DATA,
WITH A RADIUS OF 6370997 METERS!!!" on the GLCF page as the MODIS sphere is
with radius 6371007.181 according to
 http://edcdaac.usgs.gov/landdaac/tools/mrtswath/info/ReleaseNotes.pdf
 http://s2k.gsfc.nasa.gov/html_pages/groups/sat/modis_land_overview.html

Moreover, 6370997.0 is the Normal Sphere, not the MODIS sphere:
cs2cs -le | grep 6370997
   sphere a=6370997.0      b=6370997.0      Normal Sphere (r=6370997)

But who cares, we can only trust the metadata here.

Importing within Spearfish into a new location I can reproduce
the error message:
r.in.gdal in=US.Albers.2005145.ndvi.tif out=ndvi2005145 loc=albers_usa
WARNING: Datum 'Not_specified_based_on_Authalic_Sphere' not recognised by
         GRASS and no parameters found. Datum transformation will not be
         possible using this projection information.

Restarting GRASS with ther new location, I get
GRASS 6.1.cvs (albers_usa):/tmp > g.proj -p
-PROJ_INFO-------------------------------------------------
name       : Albers Equal Area
proj       : aea
a          : 6370997
es         : -inf
lat_1      : 29.5
lat_2      : 45.5
lat_0      : 0
lon_0      : -96
x_0        : 0
y_0        : 0
no_defs    : defined
-PROJ_UNITS------------------------------------------------
unit       : metre
units      : metres
meters     : 1

GRASS 6.1.cvs (albers_usa):/tmp > g.proj -w
ERROR: Invalid ellipsoid descriptors (a, rf, es or b) in file

This doesn't look good. Apparently fix is needed.