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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>HI All,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I think I may have discovered a slight issue with how GDAL reads GRIB2 files.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I created a grib2 file using a third party utility with the following parameters:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal> cell_size_x = 0.011232419944023<o:p></o:p></p><p class=MsoNormal> cell_size_y = 0.011232419944023<o:p></o:p></p><p class=MsoNormal> lat_lower_left = 41.2972846<o:p></o:p></p><p class=MsoNormal> lon_lower_left = -23.5278783<o:p></o:p></p><p class=MsoNormal> lat_upper_right = 61.5044080<o:p></o:p></p><p class=MsoNormal> lon_upper_right = 26.8045955<o:p></o:p></p><p class=MsoNormal> rows = 1799;<o:p></o:p></p><p class=MsoNormal> columns = 4481<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>When I look at the grid dimensions using wgrib2 I see that the corner points match exactly:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>1:0:grid_template=0:winds(N/S):<o:p></o:p></p><p class=MsoNormal> lat-lon grid:(4481 x 1799) units 1e-06 input WE:SN output WE:SN res 48<o:p></o:p></p><p class=MsoNormal><b> lat 41.297283 to 61.504407 by 0.011232<o:p></o:p></b></p><p class=MsoNormal><b> lon 336.472121 to 26.804594 by 0.011232</b> #points=8061319<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>When I dump the same grid using gdalinfo it’s corner points show up differently:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Driver: GRIB/GRIdded Binary (.grb)<o:p></o:p></p><p class=MsoNormal>Files: image_combine_20101115164227.grib2<o:p></o:p></p><p class=MsoNormal>Size is 4481, 1799<o:p></o:p></p><p class=MsoNormal>Coordinate System is:<o:p></o:p></p><p class=MsoNormal>GEOGCS["Coordinate System imported from GRIB file",<o:p></o:p></p><p class=MsoNormal> DATUM["unknown",<o:p></o:p></p><p class=MsoNormal> SPHEROID["Sphere",6367470,0]],<o:p></o:p></p><p class=MsoNormal> PRIMEM["Greenwich",0],<o:p></o:p></p><p class=MsoNormal> UNIT["degree",0.0174532925199433]]<o:p></o:p></p><p class=MsoNormal>Origin = (336.472120999999959,61.492418999999998)<o:p></o:p></p><p class=MsoNormal>Pixel Size = (0.011232000000000,-0.011232000000000)<o:p></o:p></p><p class=MsoNormal>Corner Coordinates:<o:p></o:p></p><p class=MsoNormal><b>Upper Left ( 336.472, 61.492) (336d28'19.64"E, 61d29'32.71"N)<o:p></o:p></b></p><p class=MsoNormal><b>Lower Left ( 336.472, 41.286) (336d28'19.64"E, 41d17'9.78"N)<o:p></o:p></b></p><p class=MsoNormal><b>Upper Right ( 386.803, 61.492) (386d48'9.77"E, 61d29'32.71"N)<o:p></o:p></b></p><p class=MsoNormal><b>Lower Right ( 386.803, 41.286) (386d48'9.77"E, 41d17'9.78"N)<o:p></o:p></b></p><p class=MsoNormal>Center ( 361.637, 51.389) (361d38'14.70"E, 51d23'21.25"N)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I thought that GDAL used degrib to extract the Grib information and so I also dumped the file with degrib and it matches the wgrib2 output as it should:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>GDS | Number of Points | 8061319<o:p></o:p></p><p class=MsoNormal>GDS | Projection Type | 0 (Latitude/Longitude)<o:p></o:p></p><p class=MsoNormal>GDS | Shape of Earth | sphere<o:p></o:p></p><p class=MsoNormal>GDS | Radius | 6367.470000 (km)<o:p></o:p></p><p class=MsoNormal>GDS | Nx (Number of points on parallel) | 4481<o:p></o:p></p><p class=MsoNormal>GDS | Ny (Number of points on meridian) | 1799<o:p></o:p></p><p class=MsoNormal><b>GDS | Lat1 | 41.297440<o:p></o:p></b></p><p class=MsoNormal><b>GDS | Lon1 | 334.942119<o:p></o:p></b></p><p class=MsoNormal><b>GDS | u/v vectors relative to | easterly/northerly<o:p></o:p></b></p><p class=MsoNormal><b>GDS | Lat2 | 61.504407<o:p></o:p></b></p><p class=MsoNormal><b>GDS | Lon2 | 25.274208<o:p></o:p></b></p><p class=MsoNormal>GDS | Dx | 0.011199 (degrees)<o:p></o:p></p><p class=MsoNormal>GDS | Dy | 0.011199 (degrees)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>My question is….How does GDAL calculate its dimensional constraints? I would have assumed that it read it right from the grib2 file.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>Bill<o:p></o:p></p></div></body></html>