[gdal-dev] reprojecting coastcolour (/meris) using python via GCPs

[Ivan Price]

Hi again Etienne,

sorry for being vague.. when i say it 'works' in inverted commas, its because i'm not sure to what level it is expected to work. I can read the list of bands but there is no georeferencing for example., gdal doesn't see the gcps (=values in lat/lon variables).

so previously i was writing out a (subsetted) gtiff with gcps in python then warping using gdalwarp -tps which was working well actually.. just a few more steps than i'd ideally like.

following your advice regarding the vrt and after learning from nansat examples (thanks Anton!) i now write a vrt with gcps and use gdalwarp from the commandline with -tps on that.. which works fine.. although i need to use a gcp for every > 200 pixels or the calculation time is too high.


if you tell me that the gcps should be recognised automatically by gdal then i'd be happy to file a bug and upload some sample data.

for info i'm using gdal 1.9.2, built by me using flags:
--prefix --with-python --pymoddir=xxx
and thats all.

thanks for your assistance,

-i

save.nc is an untouched coastcolour dataset.

(price at nemo:)$ gdalinfo NETCDF:"save.nc":reflec_1
Driver: netCDF/Network Common Data Format
Files: none associated
Size is 4481, 9921
Coordinate System is `'
Metadata:
  NC_GLOBAL#auto_grouping=reflec:norm_reflec:atm_tau
  NC_GLOBAL#Conventions=CF-1.4
  NC_GLOBAL#metadata_profile=beam
  NC_GLOBAL#metadata_version=0.5
  NC_GLOBAL#product_type=MER_FSG_CCL2R
  NC_GLOBAL#start_date=08-FEB-2011 10:37:07.984543
  NC_GLOBAL#stop_date=08-FEB-2011 10:44:24.434783
  NC_GLOBAL#TileSize=16:4481
  NC_GLOBAL#title=MERIS CoastColour L2R
  reflec_1#bandwidth=9.9370003
  reflec_1#coordinates=lat lon
  reflec_1#long_name=Water leaving irradiance reflectance at 412.691 nm
  reflec_1#solar_flux=1764.0343
  reflec_1#spectral_band_index=0
  reflec_1#units=sr^-1
  reflec_1#valid_pixel_expression=!l2r_flags.INPUT_INVALID
  reflec_1#wavelength=412.69101
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0, 9921.0)
Upper Right ( 4481.0,    0.0)
Lower Right ( 4481.0, 9921.0)
Center      ( 2240.5, 4960.5)
Band 1 Block=4481x1 Type=Float32, ColorInterp=Undefined
  NoData Value=9.96920996838686905e+36
  Metadata:
    bandwidth=9.9370003
    coordinates=lat lon
    long_name=Water leaving irradiance reflectance at 412.691 nm
    NETCDF_VARNAME=reflec_1
    solar_flux=1764.0343
    spectral_band_index=0
    units=sr^-1
    valid_pixel_expression=!l2r_flags.INPUT_INVALID
    wavelength=412.69101


(price at nemo:)$ gdalwarp -t_srs EPSG:4326  NETCDF:"save.nc":reflec_1 foo.tif
Processing input file NETCDF:save.nc:reflec_1.
ERROR 1: Unable to compute a transformation between pixel/line
and georeferenced coordinates for NETCDF:save.nc:reflec_1.
There is no affine transformation and no GCPs.




De : Etienne Tourigny [mailto:etourigny.dev at gmail.com]
Envoyé : Monday, 17 February 2014 20:32
À : Ivan Price
Cc : gdal-dev at lists.osgeo.org
Objet : Re: [gdal-dev] reprojecting coastcolour (/meris) using python via GCPs



On Mon, Feb 17, 2014 at 2:03 PM, Ivan Price <Ivan.Price at noveltis.fr<mailto:Ivan.Price at noveltis.fr>> wrote:
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'.

does it really work or sort of? If not, please file a bug report with an example data set attached or a link to it.


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..

have you tried using a .vrt file?


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

thanks for your response,

-i



De : Etienne Tourigny [mailto:etourigny.dev at gmail.com<mailto:etourigny.dev at gmail.com>]
Envoyé : Monday, 17 February 2014 14:09
À : Ivan Price
Cc : gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>

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 <Ivan.Price at noveltis.fr<mailto:Ivan.Price at noveltis.fr>> 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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