AW: [Qgis-user] managing topomaps (need a better workflow)

[Ziegler Stefan]

Hi

you probably want to try RasterLite:

http://lists.osgeo.org/pipermail/qgis-developer/2010-July/010492.html

I've never used it by myself.


mit freundlichem Gruss
Stefan Ziegler


----- Originalnachricht -----
Von: "maning sambale" <emmanuel.sambale at gmail.com>
Gesendet: Mon, 2.8.2010 13:46
An: qgis-user <qgis-user at lists.osgeo.org>
Betreff: [Qgis-user] managing topomaps (need a better workflow)

Hi,

A brief of background.  We have thousands of scanned rectified
topomaps (mostly jpegs with jgw),  In order to view them
simultaneously, I use gdal VRT.  Although this approach allows me to
view the whole collection as a single data layer, loading them at
startup is incredibly slow and even during panning around the map
view.  Another issue is that vrt and rasters in general cannot be
loaded on the fly.

Now, I need to use the several rasters in another projection.
Re-projecting the whole vrt mosaic  produces a very large GTif.

I have this workaround.
1. Open a qgis session with the vrt mosaic's projection and open the vrt mosaic.
2. Zoom to area of interest and create a new tif file using raster
tools clipper (a gui for gdal_merge)
3. Load the created tif file and reproject to the desired projection
using gdal_warp.
4. Open a new QGIS session to load re-projected raster and other layers.

I'm trying another option which is to re-project the vrt to another
vrt but this doesn't solve slow loading problem.  Re-projecting all
the individual tile can probably make it faster but you get the same
issue when you start working on another projection.

I tried the WMS route which makes it easier to load specific area in
QGIS.  However,  sharing the raster layer to colleagues as a file (for
offline viewing) will go through the above steps.

Any ideas in managing topomap collection?  I'm looking for a process
that would probably make it tedious as one time conversion, but
hopefully help us easily manage the data with the following use
scenarios:
 -  easily load the mosaic in different projections
 - select a bbox to clip and save to another raster format.



-- 
cheers,
maning
------------------------------------------------------
"Freedom is still the most radical idea of all" -N.Branden
wiki: http://esambale.wikispaces.com/
blog: http://epsg4253.wordpress.com/
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