Georeference problem with Envisat Images

[timatkinson]

Gdal 1.6.2 (as featured in Fedora 13) and gdal 1.7.2 (as featured in Ubuntu 10.4) both have a problem with Georeference of Envisat Images

It appears they are reading both the Geolocation grid ADS (correct) and the Doppler Centroid Grid (incorrect) as GCPs.

The numbers in the grids are similar but actually different and hence you get two sets of ground coordinates per one GCP Line,Column

Run the command line below (*.N1 any envisat file will do)

gdalinfo *.N1 | grep \(0.5,0.5\) and you'll instantly see the problem

[warmerdam]

Chaitanya,

Could you see if you can find envisat data to replicate this? It may be hard to find some.

[chaitanya]

Tim,

Can you provide some sample data? You can email it to me (chaitanya.ch * gmail.com) if you want it to be confidential.

[chaitanya]

I was able to reproduce the problem with a sample dataset from Anders Berg. I'm working on this.

[knutfrode]

For Envisat ASAR, the mistake is that the parameter "line_num" of Geolocation Grid is used as the Y-coordinate (tested with gdalinfo v1.7). In the ESA documentation for ASAR Level 1 products, there is a warning that "line_num" is the line number relative to the "granule within the slice", and not of the image itself. ​http://envisat.esa.int/handbooks/asar/CNTR6-6-9.htm#eph.asar.asardf.asarrec.ASAR_Geo_Grid_ADSR

Instead, the Y-coordinate should be calculated as a cumulative sum from the "num_lines" parameter: [1 cumsum(num_lines)] in Matlab-notation.

Note that Ticket #3160 refers to the same issue. A patch is posted there, but I am not sure if that solves the issue.

I propose to increase the priority of this ticket, as Envisat is one of the major satellites, and the data are not very useful without georeferencing.

[Even Rouault]

(I see you've cc'ed me. Just to mention I have no particular competence/interest on this file format and don't intend to take any particular action on this)

[knutfrode]

I have recompiled GDAL with the patch which was posted by Antonio in Ticket #3160, and can confirm that it solves the problem.

Are there any developers who would like to apply this patch to the official repository, and then close these two tickets (#3160 and #3709)?

http://trac.osgeo.org/gdal/attachment/ticket/3160/gdal-envisat-gcp.patch

[warmerdam]

Patch applied in trunk (r22289) and 1.8 branch (r22290). Tested by a user in #3709, but not actually tested by me.