[gdal-dev] gdal_translate pixel shift?

[ggp08ctl]

Hello,

I am in the process of using some Gebco bathymetry data for a project,
visualising it with Arcgis 9.3. I am using osgeo4w/ gdal to convert the
gebco netcdf file to a geotif, for use in arcmap.

I wondered if someone might be able to offer a hint to a relative beginner?
I am having what I think is a projection issue with the gebco data, as
translated in gdal using the command 'gdal_translate -a_srs EPSG:4326
gebco_08.nc'.

As part of my project, I have converted the gebco_08 data from nc to tif,
and then removed the srtm30 land topography that is part of the gebco file,
so as to just use the bathymetry data, and then added the higher resolution
esri supplied srtm3 land topography data instead. I notice that once I have
converted and displayed the gebco file (now a tif) in arcmap, that it does
not align neatly with the edge of the srtm3 data. Even when taking into
account the difference in pixel size between the two datasets there is still
a displacement between the two, with the gebco appearing 'shifted' too far
north or north-west relative to the srtm3 by as much as maybe approx one
gebco pixel. Both datasets are lat long GCS_WGS_1984. Can anyone offer me
advice as to what might be causing this. I wonder if there  might be a bug
in the gdal_translate package, or whether EPSG:4326 is the most accurate
projection for me to use in this instance. I would really appreciate any
advice, especially if I am missing something obvious.

Regards,
Chris

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