[Gdal-dev] matching metadata for different file formats

[Matt Fearon]

Hi All,

Wondering if anyone could give me some advice on the following. Sjur was 
helping me, but has gone on holiday.

I have a grib file that I have converted to a netcdf. My goal is to 
reproject the data in the netcdf file from polar stereographic to 
geographic. The original grib file reprojects nicely using the following 
GDAL command;

gdalwarp -t_srs '+proj=latlong +datum=WGS84' gag4.19980201.01 out_geo.tif

However, the netcdf file does not reproject correctly. I believe it is 
due to metadata being lost. The only difference between the 2 files are 
the format, metadata, and the data values - after some calculations on 
the data. The coordinate system, projection, and datum etc.. are the 
same. How can I make the metadata consistent between the 2 files using 
GDAL commands and reproject accurately? I have tried many things 
unsuccessfully. Please see below the following:
1. gdalinfo on grib file
2. gdalinfo on netcdf file before gdal_translate
3. gdalinfo on geotiff after gdal_translate (an attempt to make metadata 
consistent)

Help would be greatly appreciated.
thanks,
Matt


---- gdalinfo on grib file:

Driver: GRIB/GRIdded Binary (.grb)
Files: gag4.19980201.01
Size is 1160, 880
Coordinate System is:
PROJCS["unnamed",
   GEOGCS["Coordinate System imported from GRIB file",
       DATUM["unknown",
           SPHEROID["Sphere",6371200,0]],
       PRIMEM["Greenwich",0],
       UNIT["degree",0.0174532925199433]],
   PROJECTION["Polar_Stereographic"],
   PARAMETER["latitude_of_origin",60],
   PARAMETER["central_meridian",255],
   PARAMETER["scale_factor",90],
   PARAMETER["false_easting",0],
   PARAMETER["false_northing",0]]
Origin = (-2095445.938568701269105,-3433257.108374913223088)
Pixel Size = (4763.000000000000000,-4763.000000000000000)
Corner Coordinates:
Upper Left  (-2095445.939,-3433257.108) (136d23'50.23"W, 52d37'0.31"N)
Lower Left  (-2095445.939,-7624697.108) (120d22'0.66"W, 22d44'35.90"N)
Upper Right ( 3429634.061,-3433257.108) ( 60d 1'48.89"W, 45d35'28.48"N)
Lower Right ( 3429634.061,-7624697.108) ( 80d46'53.41"W, 19d46'5.69"N)
Center      (  667094.061,-5528977.108) ( 98d 7'13.01"W, 39d48'1.57"N)
Band 1 Block=1160x1 Type=Float64, ColorInterp=Undefined
 Description = 0[-] SFC (Ground or water surface)



---- gdalinfo on netcdf before gdal_translate. Note metadata on the 
coordinate system, datum, projection, and corners have been lost when 
compared to grib.

Driver: netCDF/Network Common Data Format
Files: 19980201.nc
Size is 1160, 880
Coordinate System is `'
Metadata:
 precip#_FillValue=-9.990000e+02
 precip#description=These daily data are a sum of the original hourly 
data; the sum used a GMT to UTC time adjustment (15 deg change longitude 
= 1 hour change in GMT); the adjustment was calculated per individual 
gridcell determining the linear distance between centroid longitude and 
the prime meridian
 precip#date=19980201
 precip#longname=Daily Precipitation
 precip#shortname=precip
 precip#center=US National Weather Service - NCEP (WMC)
 precip#long_name=Total precipitation
 precip#units=kg/m2
 precip#coordinates=gridlat_240 gridlon_240
 precip#level_indicator=1
 precip#gds_grid_type=5
 precip#parameter_table_version=2
 precip#parameter_number=61
 precip#model=WSR-88D Stage II Precipitation Analysis
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,  880.0)
Upper Right ( 1160.0,    0.0)
Lower Right ( 1160.0,  880.0)
Center      (  580.0,  440.0)
Band 1 Block=1160x1 Type=Float32, ColorInterp=Undefined
 NoData Value=-999
 Metadata:
   NETCDF_VARNAME=precip


---- gdalinfo on geotiff after the following gdal_translate command. 
Note how GEOGCS says "unnamed ellipse" and Spheroid says "unnamed". 
These are different when compared to the grib. Grib has these as 
"sphere". How can I change these to "sphere" and keep the radii = 
6371200 km ?

gdal_translate -sds -a_srs '+proj=stere +lat_ts=60 +lat_0=90 +lon_0=255 
+k_0=90 +x_0=0 +y_0=0 +a=6371200 +b=6371200' -a_ullr -2095445.939 
-3433257.108 3429634.061 -7624697.108 19980201.nc 19980201.tif


Files: 19980201.tif
Size is 1160, 880
Coordinate System is:
PROJCS["unnamed",
   GEOGCS["unnamed ellipse",
       DATUM["unknown",
           SPHEROID["unnamed",6371200,0]],
       PRIMEM["Greenwich",0],
       UNIT["degree",0.0174532925199433]],
   PROJECTION["Polar_Stereographic"],
   PARAMETER["latitude_of_origin",60],
   PARAMETER["central_meridian",255],
   PARAMETER["scale_factor",90],
   PARAMETER["false_easting",0],
   PARAMETER["false_northing",0],
   UNIT["metre",1,
       AUTHORITY["EPSG","9001"]]]
Origin = (-2095445.939000000013039,-3433257.108000000007451)
Pixel Size = (4763.000000000000000,-4763.000000000000000)
Metadata:
 AREA_OR_POINT=Area
 precip#_FillValue=-9.990000e+02
 precip#description=These daily data are a sum of the original hourly 
data; the sum used a GMT to UTC time adjustment (15 deg change longitude 
= 1 hour change in GMT); the adjustment was calculated per individual 
gridcell determining the linear distance between centroid longitude and 
the prime meridian
 precip#date=19980201
 precip#longname=Daily Precipitation
 precip#shortname=precip
 precip#center=US National Weather Service - NCEP (WMC)
 precip#long_name=Total precipitation
 precip#units=kg/m2
 precip#coordinates=gridlat_240 gridlon_240
 precip#level_indicator=1
 precip#gds_grid_type=5
 precip#parameter_table_version=2
 precip#parameter_number=61
 precip#model=WSR-88D Stage II Precipitation Analysis
Corner Coordinates:
Upper Left  (-2095445.939,-3433257.108) (136d23'50.23"W, 52d37'0.31"N)
Lower Left  (-2095445.939,-7624697.108) (120d22'0.66"W, 22d44'35.90"N)
Upper Right ( 3429634.061,-3433257.108) ( 60d 1'48.89"W, 45d35'28.48"N)
Lower Right ( 3429634.061,-7624697.108) ( 80d46'53.41"W, 19d46'5.69"N)
Center      (  667094.061,-5528977.108) ( 98d 7'13.01"W, 39d48'1.57"N)
Band 1 Block=1160x1 Type=Float32, ColorInterp=Gray
 NoData Value=-999
 Metadata:
   NETCDF_VARNAME=precip