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