[gdal-dev] onestep vs twostep reproject and change format

[Etienne Tourigny]

See http://trac.osgeo.org/gdal/ticket/4484

On Tue, Jan 29, 2013 at 6:19 AM, Even Rouault
<even.rouault at mines-paris.org> wrote:
> Selon Terry Rankine <terry.rankine at csiro.au>:
>
>> Hi Guys
>>
>> I have an ERS (ermapper) dataset I want to reproject into wsg84 and then
>> change the file format to netcdf4. I am using GDAL 1.9.2 linked against
>> netcdf 4.1.3
>>
>> I get different results using the following.
>>
>> One step:
>> * gdalwarp /projects/r17/GA/GSQ_P1247tmig.ers -s_srs "+proj=latlong
>> +datum=GDA94" -t_srs "+proj=latlong +datum=WGS84" -r cubic -of NETCDF
>> -overwrite -co "FORMAT=NC4" -co "COMPRESS=DEFLATE" -co "ZLEVEL=9" -dstnodata
>> -99999 onestep.nc4
>>
>> Two step
>> * gdalwarp -of ERS -s_srs "+proj=latlong +datum=GDA94" -t_srs "+proj=latlong
>> +datum=WGS84" -r cubic /projects/r17/GA/GSQ_P1247tmig.ers reproj.ers
>> -dstnodata -99999
>> * gdal_translate -of netCDF -co "FORMAT=NC4" -co "COMPRESS=DEFLATE" -co
>> "ZLEVEL=9" -stats reproj.ers reproj.nc4
>>
>> In fact - the onestep destroys part of my data.
>> OneStep output
>> <http://osgeo-org.1560.n6.nabble.com/file/n5030451/onestep.nc4>
>>
>> two step output:
>> <http://osgeo-org.1560.n6.nabble.com/file/n5030451/reproj.nc4>
>>
>> Can someone let me know what I am doing wrong?
>
> Nothing. The netCDF driver would need enhancements to fully support random
> writing. I believe there are already tickets in Trac about that, or there was a
> related discussion on that topic some time ago. The 2 step method is the
> recommanded one for the time being.
>
> For the one step process, you could perhaps try adding -wo OPTIMIZE_SIZE=TRUE
> (see
> http://gdal.org/structGDALWarpOptions.html#a0ed77f9917bb96c7a9aabd73d4d06e08 ).
> This will perhaps work, but at the expense of a slow warping in some situations.
>
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