[gdal-dev] Can VRT be used to control display order of images in mosaic?

[Roger André]

Hi Frank,

Thanks for the reply.  It might be worth keeping the option to control layer
ordering somehow in a mosaic.  The reason I'm exploring this is to see if
it's possible to emulate the ArcGIS 10 "closest to center" behavior.  I'm
thinking that if I dynamically write the VRT, I can control how images are
overlapped in response to the BBOX extents specified in a WMS request.

Roger
--

On Tue, Jun 22, 2010 at 8:16 AM, Frank Warmerdam <warmerdam at pobox.com>wrote:

> Roger André wrote:
>
>> Hi All,
>>
>> I'd like to control the order in which overlapping images are displayed in
>> a mosaic.  Is it possible to do that by using a VRT, and altering the order
>> in which the files are defined in it?
>>
>> The online doc for gdalbuildvrt states, "If there is some amount of
>> spatial overlapping between files, the order may depend on the order they
>> are inserted in the VRT file, but this behaviour should not be relied on."
>>
>> Not sure if this disclaimer is for the gdalbuildvrt utility, or describes
>> the generic behavior of a raster VRT.
>>
>
> Roger,
>
> I believe the statement applies to the VRT format itself.  I have looked
> at the code, and it always applies them linearly based on the order they
> appear in the .VRT list of sources.  I think you could depend on it "for
> now"
> though in a future version we might do something more fancy that would
> result in alternate ordering.
>
> Best regards,
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam<http://pobox.com/%7Ewarmerdam>
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/gdal-dev/attachments/20100622/b73b7db0/attachment.html