Hi all,
I have been trying to override the MODIS WKT definition (derived from
the source HDF4 files using gdal_translate), which apparently is not
sufficient for correct transformations.
The correct srs is '+proj=sinu +R=6371007.181 +nadgrids=@null
+wktext', whereas the one stored in GTiff files is '+proj=sinu
+lon_0=0 +x_0=0 +y_0=0 +a=6371007.181 +b=6371007.181 +units=m +no_defs
'
I tried to override the projection ref with gdal_translate, but the
resulting file (in GTiff format) does not keep the EXTENSION nodes.
Examples below.
Is this a limitation of GTiff format that cannot be fixed? Is there
another format (except VRT) that can keep EXTENSION nodes?
The workaround is to override the SRS with -s_srs='...' when a
transformation is needed, but it would be better if the file itself
could store that information.
thanks,
Etienne
$ gdal_translate -a_srs '+proj=sinu +R=6371007.181 +nadgrids=@null
+wktext' MCD12Q1.IGBP.h11v07.2002.tif tmp2.tif
$ gdalsrsinfo tmp2.tif
PROJ.4 : '+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181
+b=6371007.181 +units=m +no_defs '
OGC WKT :
PROJCS["unnamed",
GEOGCS["unnamed ellipse",
DATUM["unknown",
SPHEROID["unnamed",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["metre",1,
AUTHORITY["EPSG","9001"]]]
which is the same(almost) as the input file:
$ gdalsrsinfo MCD12Q1.IGBP.h11v07.2002.tif
PROJ.4 : '+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181
+b=6371007.181 +units=m +no_defs '
OGC WKT :
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["metre",1,
AUTHORITY["EPSG","9001"]]]
However, using vrt format shows that gdal_translate does set the
output srs correctly:
$ gdal_translate -of vrt -co COMPRESS=DEFLATE -a_nodata 255 -a_srs
'+proj=sinu +R=6371007.181 +nadgrids=@null +wktext'
MCD12Q1.IGBP.h11v07.2002.tif tmp2.vrt
$ gdalsrsinfo tmp2.vrt
PROJ.4 : '+proj=sinu +R=6371007.181 +nadgrids=@null +wktext'
OGC WKT :
PROJCS["unnamed",
GEOGCS["unnamed ellipse",
DATUM["unknown",
SPHEROID["unnamed",6371007.181,0],
EXTENSION["PROJ4_GRIDS","@null"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]],
PROJECTION["Sinusoidal"],
PARAMETER["longitude_of_center",0],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
EXTENSION["PROJ4","+proj=sinu +R=6371007.181 +nadgrids=@null +wktext"]]
For reference here is how I generate the GTiff from HDF4 files (similar to
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