[Gdal-dev] SoC: GDAL2Tiles: georeferenced rasters on the web

[Klokan Petr Přidal]

Hello,

I am working on the Google SoC project GDAL2Tiles, which should allow
to use GDAL library for simply exporting raster files with
georeference into the web and viewing by Google Maps, Google Earth,
OpenLayers, WorldKit, ...

I see the main goal of my project in implementation of an application,
which allow to convert a raster georeferenced map into a directory
with tiles and metadata. Such structure should, after uploading to any
webserver, allow on-line accessing from different viewers.

I have found a commercial project Arc2Earth, a module for ESRI
ArcView, which implement similar functionality.

There are several things I realized in last month, which a bit changed
my look at the project and that implied some goals as important for
the final result, so let's discuss them here:

If a man need to publish raster map, usually there is several map
sheets that needs to be merged together, merging in gdal using
gdal_merge.py is beautiful, but raster should be reprojected in
advance. Another thing is that merging of small overlapping raster
tiles could be more efficient then merging whole map sheets especially
for huge raster results.

There is a project GeoQuadTree.org, which implements this reprojection
and merging functionality on tile level using GDAL library.
This project define own GeoQuadTree tile structure, and also
implements GDAL reader driver for this structure as well as simple
FastCGI WMS server.
These tools were available under GPL, which was a bit restricting for
practical usage in GDAL library (linking with proprietary libraries
like MrSID, linking into commercial applications, etc.).
I was speaking with Jordi, author of these tools, and he accepted dual
licensing (GPL and the same license like GDAL has), so now gqt tool
and driver could be merged into official GDAL tree.
Is there some reason why not to do that?

To be true I like the GQT tile structure more that TMS tile structure,
I will write an extra email with reasons why.

Practical tasks to reach main goals of SoC Project I see now at:

- Prepare nice coded HTML/CSS/JavaScript examples of inserting tiles
into viewers (useful for both GQT and TMS with global-geodetic
profile).
I've been playing with this so far, I prepare some testing maps by
Arc2Earth Trial. Unfortunately we can't use JavaScript from this
project (and anyway I would like to make them better, now Safari is
not supported for example... and code is cryptic).
Testing map is available at:
http://www.staremapy.cz/a2e/FreeGeoDataCZAll/
I am working on it this week and I would like to have that on Sunday
(first SoC deadline).

- I will prepare python script which will generate sample index.html
for given GQT structure and several viewers. This script will generate
KML files for tiles with suitable projection too.

- I was thinking about python script for conversion between tile
structure, so you can work with GQT but you can simply convert tiles
into TMS naming conversion, similar with VirtualEarth, Zoomify,
anything else later. This script will just create metadata and rename
tiles and directories.

- I would like to add profiles from TMS (<global-geodetic> EPSG:4326 -
used by Google Earth and NASA WorldWind, and <global-mercator>
EPSG:41001 - for Google Maps, OpenLayers, MS Virtual Earth, etc) into
gqt stable (0.9) tool.
After conversation with Jordi I will need to make other small patches
to this tool, I think of direct (one step) conversion of one file into
the given profile, and some more functionality.
Stable 0.9 version is for me more important. I need only .png tiles now.
Version 1.0 adds support for more layers (multibands) in one tile
structure, separate mask, and tile file formats another then png.

- In Google SoC I promised a driver for writing the tile structure, I
hope this will be finished too. But I see more practical to
concentrate on GQT and metadata, then look at driver, as GQT tool now
do that job pretty well.

After the project is finished I would love to see gqt tool and python
scripts in FWTools.

Any comments?

Klokan