[Gvsig_english] Georeferencing MrSID (.sid) format image

[Juan Lucas Dominguez Rubio]

Hi, Denis:

As Antonio says, gvSIG should read the georeference information contained in your SID files, but for some reason, it's not read (maybe it's not there?) and the raster is located at the default (0, 0).

I don't know what will happen with your 1.6 billion pixel images, but you can try this:

gdal_translate -of gtiff -co "TFW=YES" filename.sid filename.tif

Then open the file 'filename.tfw' and check if it makes sense (the last two numbers should be not equal to zero). If the tfw does not make sense, you will have to find out the coordinates of the top-left corner of your images and write the 'filename.tfw' yourself. Then you can use the tif file in gvSIG, and if it's too large, you can compress it again, for example to ECW:

gdal_translate -of ecw -co "LARGE_OK=YES" filename.tif filename.ecw

GDAL is part of FWTools: http://fwtools.maptools.org/

Regards,
 
Juan Lucas Domínguez Rubio
Prodevelop SL, Valencia (España)
Tlf.: 96.351.06.12 -- Fax: 96.351.09.68
http://www.prodevelop.es <http://www.prodevelop.es/> 

________________________________

De: gvsig_internacional-bounces at runas.cap.gva.es en nombre de Antonio Falciano
Enviado el: mié 26/11/2008 15:07
Para: Users and Developers mailing list
Asunto: Re: [Gvsig_english] Georeferencing MrSID (.sid) format image



Payne Denis ha scritto:
> I have 4 large .sid format images I need to load. They are 12.5cm
> resolution aerial photography each covering 5km*5km. I'm working in UK
> Nat Grid, and using gvsig 1.1.2
>
> They open OK - but not properly position. They show as being at the
> origin. I have tried georeferencing them - but whilst the process
> appears OK that doesn't appear to solve the problem. I have what looks
> like a valid .rmf file from that process.
>
> I've tried using IrfranView to convert to .jpg format, but that doesn't
> retain the resolution of the original .sid format images.
>
> I'd welcome any suggestions as to how I can get these, at full
> resolution, properly positioned, into gvsig

Hi Denis,
you can convert them into another format using GDAL:
http://www.gdal.org/gdal_translate.html

The explanation of this apparently strange behaviour is that...

>> The key point here its: if the files are geospatial ones (geotiff and
>> MrSID), gvSIG will use the internal information. If they are no
>> geospatial ones (standard tiff and jpeg, by instance) gvSIG will use
>> external world files as this is the only way to georeferencing them
from http://www.nabble.com/Re%3A-Problemi-con-file-MrSID-p15484600.html

Regards,
Antonio






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