[gdal-dev] GSoC GDAL2Tiles: MapTiler.org, Google Maps Projection Web, Source Code

Klokan Petr Přidal klokan at klokan.cz
Mon Aug 18 16:23:44 EDT 2008

Hello everybody,

what was done recently on GDAL2Tiles project:

New cool example of the map generated by GDAL2Tiles:
I processed freely available USGS DRG map of Grand Canyon by
GDAL2Tiles. It is a nice example of what GDAL2Tiles can generate:


Source Code:
- Fully functional source code for generating Google Maps tiles is in
my GDAL SVN sandbox (http://svn.osgeo.org/gdal/sandbox/klokan/).
The code was refactored a lot and it is almost prepared for merging to
stable svn trunk gdal2tiles.py, but some coding is still needed. I am
going to work on it during the next week.

- I split the code into three files: 'gdal2tiles.py' (the main command
line utility), then 'globalmaptiles.py' (classes for global
mercator/geodetic tile bounds calculation, runs as command line
utility too), and supporting module 'templates.py' with sample HTML
viewers and base for generated XML files.

- Implementation of several resampling algorithms for controlling the
quality of tile rendering. Default is 'average' used in the GDAL's
overview functionality. Complete list is:
The last one is high quality Lanczos based antialiasing algorithm, but
you will need Python Image Library for that.
Quality of the tile rendering is excellent I think. If you need it,
the simple and fast 'near' it is still available.

- GDAL2Tiles generates the sample Google Maps Based viewer, OpenLayers
based Overlay viewer and KML files for Google Earth.

- The utility automatically warp the raster to Google Maps projection
(EPSG:900913) by AutoCreateWarpedVRT().

- For raster files with palette (USGS DRG, NOAA BSB, ...) a separate
VRT with "rasterize rgba" (GDAL 1.6dev) is recommended (later I would
like to automate this step).

The code is NOT YET READY for production use (now supports only RGBA -
4 bands - source files for example), so I recommend you to wait for
merged version which will appear in the GDAL trunk. I will send a note
when I will finish the merging.

Documetation & MapTiler.org

- I decided to create a special website for distributing binary
installer and user-friendly GUI for GDAL2Tiles. I plan to develop
wxWidget based GUI a la step by step wizard. The user-friendly project
has name MapTiler, http://www.MapTiler.org/. Right now this web is
used only for documentation on for raster files for templates, which I
did not want to distribute with utility.

I received great feedback from several users and realized that
GDAL2Tiles utility is expected by community. That pushed me to crete
this new project and change the name to MapTiler, which is more
straightforward and fits to the utility probably better, especially
for users who are not familiar with GDAL tools yet.
GDAL2Tiles will be maintained as GDAL command line utility. MapTiler
will implement just GUI and binary distribution.

It would be great to have blessing of OSGEO for this project, I would
prefer to not make separate SVN repository for such small project,
better to keep it as part of GDAL. Would it be possible? Otherwise I
will create Google Code project.

- I studied the OpenGIS proposal for WMTS standard, which is related
to TMS and I plan to send some comments to that standard. Is there
still free OSGEO slot for OpenGIS membership?

- I created a website about Spherical Mercator and Google Maps
Projection and Coordinate system, for anybody who is interested to see
the math behind tiles:

Question to community:

- Would it be possible to keep more files separately even in the main
GDAL tree or the utility really have to be merged to one file?

- Is there anybody in the OpenLayers community who whould like to have
a look at the Opacity Control for OL? I prepared the bitmaps. Is there
any need on the OpenLayers templates? Now I am using /dev/ tree of
OpenLayers as Virtual Earth support is broken in the stable tree
(Safari for example).

- Does anybody know how to correctly set the KML SuperOverlay
maxlodpixels and fadeextents so transparency and opacity runs well and
tiles are not disappearing in Google Earth?

- Is anybody interested to help me with developing MapTiler (for
example compilation of latest GDAL with all modules, preparing of
Windows installer, help with wxPython...)
KyngChaos (thank you!) already had a look at binaries for MacOSX, but
we did not moved far yet as I need some functionality from 1.6dev.

Thanks belong to everybody who gave me excellent advices on #gdal IRC,
especially to 'FrankW' and 'even'.

BTW I am looking for an interesting job or paid projects... any offers? ;-)

Is there anybody who would like to support further development of
MapTiler/GDAL2Tiles? There is plenty of features on todo list (merging
of produced tiles with existing tile tree, support for MapCruncher
tiles, Zoomify tiles, speed improvement - rewrite to C++ to allow
better usage of threads on multi-core processors, driver for remote
online TMS tiles for GDAL/MapServer to allow WMS from statically
published tiles, etc..).

Best regards...

Klokan Petr Pridal

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