[Gdal-dev] Re: GDAL and Spot Vegetation

[Vincent Schut]

Markus,

my first impression is that it should be correct. According to the faq 
(http://www.vgt.vito.be/faq/faq.html), vegetation coordinates refer to the 
center of a pixel, so your correction with 1/2 pixel size should be OK. 
That's exactly what I did, too.
About Plate Caree, I'm not sure either. I used a simple lat/long wgs84 
configuration which looked OK. It is however possible that better projection 
parameters exist... I know I found a small shift when comparing with MODIS 
data, but I had hard times trying to reproject these modis data from Goodes 
Homolosine with datum shift etc. to generic latlong, and I always suspected 
the shift to be a result of that, and not of bad spot vegetation projection 
parameters. Still do think that, by the way.

Vincent.

On Wednesday 18 August 2004 17:52, Markus Neteler wrote:
> On Wed, Aug 18, 2004 at 05:09:13PM +0200, Vincent Schut wrote:
> > On Wednesday 18 August 2004 16:56, Markus Neteler wrote:
> >
> > <snip>
> >
> > > So one seems to have to parse the 0001_LOG.TXT (sigh).
> >
> > That's what I did...
>
> Meanwhile I got a sort of valid VRT file constructed (manually).
> Not sure yet about "Plate Caree"... I used QGIS to
> overlap to VMAP0 coastline data, it matches quite well.
>
> So here my suggestion, added the spot_vegetation_ndvi.vrt file:
>
> gdalinfo spot_vegetation_ndvi.vrt
> Driver: VRT/Virtual Raster
> Size is 8177, 5601
> Coordinate System is:
> GEOGCS["wgs84",
>     DATUM["WGS_1984",
>         SPHEROID["wgs84",6378137,298.257223563],
>         TOWGS84[0.000,0.000,0.000]],
>     PRIMEM["Greenwich",0],
>     UNIT["degree",0.0174532925199433]]
> Origin = (-11.004464,75.044643)
> Pixel Size = (0.00892857,-0.00892857)
> Corner Coordinates:
> Upper Left  ( -11.0044643,  75.0446433) ( 11d 0'16.07"W, 75d 2'40.72"N)
> Lower Left  ( -11.0044643,  25.0357149) ( 11d 0'16.07"W, 25d 2'8.57"N)
> Upper Right (  62.0044641,  75.0446433) ( 62d 0'16.07"E, 75d 2'40.72"N)
> Lower Right (  62.0044641,  25.0357149) ( 62d 0'16.07"E, 25d 2'8.57"N)
> Center      (  25.4999999,  50.0401791) ( 25d30'0.00"E, 50d 2'24.64"N)
> Band 1 Block=128x128 Type=Byte, ColorInterp=Gray
>   NoData Value=0
>
> Does it look reasonable (I don't like the small deviation);
> and there is the usual cell center vs cell corners story...
>
> The file 0001/0001_LOG.TXT reports:
> [...]
> CARTO_UPPER_LEFT_X         -11.000000
> CARTO_UPPER_LEFT_Y          75.000000
> CARTO_UPPER_RIGHT_X         62.000000
> CARTO_UPPER_RIGHT_Y         75.000000
> CARTO_LOWER_RIGHT_X         62.000000
> CARTO_LOWER_RIGHT_Y         25.000000
> CARTO_LOWER_LEFT_X         -11.000000
> CARTO_LOWER_LEFT_Y          25.000000
> CARTO_CENTER_X              25.500000
> CARTO_CENTER_Y              50.000000
> CARTO_HEIGHT                50.000000
> CARTO_WIDTH                 73.000000
> GEO_UPPER_LEFT_LAT        +075.000000
> GEO_UPPER_LEFT_LONG       -011.000000
> GEO_UPPER_RIGHT_LAT       +075.000000
> GEO_UPPER_RIGHT_LONG      +062.000000
> GEO_LOWER_RIGHT_LAT       +025.000000
> GEO_LOWER_RIGHT_LONG      +062.000000
> GEO_LOWER_LEFT_LAT        +025.000000
> GEO_LOWER_LEFT_LONG       -011.000000
>
> I don't feel that the map in QGIS is shifted by 0.5 degree.
> Mmh.
>
> Please let know in case of errors in the VRT file.
>
> Markus

-- 
-----------------------------
 Vincent Schut
 SarVision B.V.
 Wageningen, The Netherlands
 www.sarvision.com