[gdal-dev] To to create HDF4 files for GDAL

[Andreas H.]

Hi again,

I played around a bit and now it's working. I needed to add four global
attributes to the HDF4 file:

- TransformationMatrix
- AREA_OR_POINT
- Projection
- Signature

What I don't understand is why Signature is needed. I mean, even without
Signature, the file contains all necessary information, but GDAL refuses
to process it. Once I add the Signature = "Created with GDAL
(http://www.remotesensing.org/gdal/)" attribute, GDAL does read the file
correctly.

I personally find this behaviour very strange. If I don't use GDAL to
create the file, but add all attributes necessary, GDAL should use these
attributes.

I created a ticket for this:

   http://trac.osgeo.org/gdal/ticket/4425

Cheers,
Andreas.


> Hi there,
>
> when creating HDF4 files outside of GDAL, which metadata do I have to
> write to
> the file such that GDAL can subsequently correctly read the data? In the
> docs
> I read that only HDF4 files created with GDAL or certain other HDF4 types
> are
> recognized. However, the files are created "by hand" using the HDF4 API
> from
> Delphi. I would like to modify this creation in a way such that GDAL can
> read
> the data.
>
> The HDF files follow the "Scientific DataSet (SDS)" standard. When reading
> the files with GDAL, it looks like this:
>
>    $ gdalinfo datafile.hdf
>    Driver: HDF4Image/HDF4 Dataset
>    Files: datafile.hdf
>    Size is 2880, 1440
>    Coordinate System is `'
>    Metadata:
>      _FillValue=-nan
>      long_name=VCDstrat NO2
>    Geolocation:
>      SRS=GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS
> 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9108"]],AUTHORITY["EPSG","4326"]]
>      X_DATASET=HDF4_SDS:UNKNOWN:"datafile.hdf":2
>      X_BAND=1
>      Y_DATASET=HDF4_SDS:UNKNOWN:"datafile.hdf":1
>      Y_BAND=1
>      PIXEL_OFFSET=0
>      PIXEL_STEP=1
>      LINE_OFFSET=0
>      LINE_STEP=1
>    Corner Coordinates:
>    Upper Left  (    0.0,    0.0)
>    Lower Left  (    0.0, 1440.0)
>    Upper Right ( 2880.0,    0.0)
>    Lower Right ( 2880.0, 1440.0)
>    Center      ( 1440.0,  720.0)
>    Band 1 Block=2880x347 Type=Float32, ColorInterp=Gray
>
> Obviously, georeferencing is not working. What do I need to do to the HDF4
> file to fix this?
>
> Thanks for your insight,
>
> Andreas.
>
>
> PS: In case anyone is interested, here's the reason why I want to do this:
>
> I have a whole lot of HDF4-SDS files which I want to plot using GMT. So I
> thought using gdal_translate to convert the HDF4 to GRD would be the
> easiest
> solution. I'm using GDAL 1.8.1 .
>
> However, I'm running into problems which I'm detailing below:
>
> I guess the problem is that GDAL doesn't read the SDS's latitude/longitude
> information. When converting this file then to GMT's grd format, I get a
> warning, which I guess doesn't really matter too much:
>
>    $ gdal_translate -of GMT datafile.hdf test.grd
>    Warning 6: A dataset opened by GDALOpenShared should have the same
> filename (datafile.hdf) and description
> (HDF4_SDS:UNKNOWN:"datafile.hdf":0)
>    Input file size is 2880, 1440
>
> The resulting grd file looks like this:
>
>    $ gdalinfo test.grd
>    Driver: GMT/GMT NetCDF Grid Format
>    Files: test.grd
>           test.grd.aux.xml
>    Size is 2880, 1440
>    Coordinate System is `'
>    Origin = (0.000000000000000,0.000000000000000)
>    Pixel Size = (1.000000000000000,1.000000000000000)
>    Metadata:
>      _FillValue=-nan
>      long_name=VCDstrat NO2
>    Corner Coordinates:
>    Upper Left  (   0.0000000,   0.0000000)
>    Lower Left  (       0.000,    1440.000)
>    Upper Right (    2880.000,       0.000)
>    Lower Right (    2880.000,    1440.000)
>    Center      (    1440.000,     720.000)
>    Band 1 Block=2880x1 Type=Float32, ColorInterp=Gray
>
> When I now try to plot this file using grdimage, I get the following:
>
>    grdimage: GMT ERROR: grid y increment <= 0.0
>    grdimage: Use grdedit -A on your grid file to make region and
> increments compatible [test.grd]
>
> However, running the suggested grdedit -A test.grd doesn't change a thing
> ...
>
>
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