Hi Etienne,

firstly the problem reading the MERIS (actually coastcolour) data was due to 
the fact i was using gdal 1.6, after upgrading to 1.9 i can at least list the 
bands so i guess that 'works'.

regarding the use of the filesystem, i tried that, however it is slow to write 
out the whole dataset to disk, (i need to treat hundreds of images), so i was 
looking for a way to avoid this.. although it will be my fallback option if all 
else fails..

either way i'll reply to the list with what we do in the end

thanks for your response,

-i



De : Etienne Tourigny [mailto:[email protected]]
Envoyé : Monday, 17 February 2014 14:09
À : Ivan Price
Cc : [email protected]
Objet : Re: [gdal-dev] reprojecting coastcolour (/meris) using python via GCPs

As far as I know, the gdal warp api is not exposed to python.

I have no idea on reading the MERIS data with the gdal netcdf driver - what I 
the problem?

But you might be able to use this workaround: instead of creating a source 
dataset using the memory driver, create a file on disk (in gtiff format) with 
GCPS and write data to disk, and then use gdalwarp on that.

Etienne

On Mon, Feb 17, 2014 at 6:46 AM, Ivan Price 
<[email protected]<mailto:[email protected]>> wrote:

Hello,

I am trying to reproject a window inside a coastcolour (=MERIS) image. As far 
as I can see GDAL cannot read the coastcolour data directly, so i am reading 
the coastcolour netcdf in python, building a source dataset using the memory 
driver, adding GCPS (1 for every 10th pixel) and writing the data to it, then 
reprojecting the source dataset to a destination dataset which is a spatial 
subset of the original in wgs84 lat/long.

This works fine and is relatively fast, but the reprojection is not accurate, 
the results are out by about 6-10 pixels (in various directions). On reading 
the forums it seems if i was using gdalwarp i would be using -tps, however the 
ReprojectImage() function does not seem to offer this parameter ? And i don't 
have the option of using the commandline tool as even gdal 1.10 cannot 
recognise the coastcolour data.

So i guess i have 2 questions.. has anyone had any success reading coastcolour 
data with the gdal command line tools, and secondly:

how can i get ReprojectImage() to be more accurate, given i have a GCP for 
every pixel ?

thanks and regards,

-ivan



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