Reprojecting a layer using gdaltindex

[Frederico Lucca]

On 9/26/06, Frank Warmerdam <warmerdam at pobox.com> wrote:
>
> Frederico Lucca wrote:
> > Hello list,
> >
> > Can I reproject a image that is inside a layer using tileindex?
>
> Frederico,
>
> Yes.
>
> > My problem is that I need to show a ECW that is in Corrego Alegre Datum.
> > First of all I tried to use
> > PROJECTION
> >    "init=epsg:4225"
> > END
> > without success.
>
> To be clear, are the bounds stored in the tile index in degrees?
> (as opposed to projected meters, feet, etc)


Frank,

Yes, the bounds are stored in degrees, with Corrego Alegre datum. Almost the
same as WGS84, in some places with difference of 60 meters from one to
other.


> Than I tried to use gdalwarp to convert it to WGS84 that is my map
> > Datum, but I can't write ECW format, why not?
>
> The gdalwarp program processes the image in chunks, but the ECW
> writer (and also many other compressed GDAL drivers) only support
> line by line copying, so gdalwarp has to output to a "working file",
> which can then be converted to ecw using gdal_translate.  I often
> use GeoTIFF or Imagine (HFA) formats for working files.


Great! The problem is the hard disk space, I have more than 1000 images and
no space. Each GeoTiff have 100.000 MB and compressing with ECW 10.000 MB.


> So, the only solution I found is convert using gdalwarp exporting as
> > GTiff, but the image size is very large.
> >
> > I have many photos and want to use only a layer if is possible.
> > There is a solution?
>
> Generally speaking, if all your photos are in EPSG:4225 you should be
> able to just label the layer that way, and your map as EPSG:4326, and
> mapserver will take care of reprojecting the images as needed.
>
> However, you cannot have a mix of coordinate systems in your tile index.
> So this only works if all the images in your tile index are in the same
> coordinate system.


Ok, all my images have the same coordinate system.


There is a performance cost to reprojecting rasters on the fly.  You
> may still find you are better pre-reprojecting them using gdalwarp,
> and then recompressing to ECW with gdal_translate.


Ok, I will try, thanks a lot.

Fred.

Good luck,
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
>
>


-- 
"Everything under the sun is in tune
But the sun is eclipsed by the moon"
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