[gdal-dev] gdal2tiles strangeness

[Klokan Petr Přidal]

Mano,

If you would like to have both Google Maps and Google Earth
presentation for a global map then you must generate two tile sets,
because Google Maps supports only Mercator tiles (EPSG:900913) and
Google Earth only geodetic (EPSG:4326).

GDAL2Tiles has as a default tile profile 'mercator', it means that it
will warp your input into Spherical Mercator internally.
To create tiles and KML for Google Earth for your EPSG:4326 input data
you should use -p "raster".

>From the "gdal2tiles --help":

-k, --force-kml     Generate KML for Google Earth - default for 'geodetic'
                        profile and 'raster' in EPSG:4326. For a dataset with
                        different projection use with caution!

Detailed description of recommended step by step usage of gdal2tiles
for global maps was posted by Jesse Varner
from CIRES & NOAA/NGDC, who used gdal2tiles for official presentation
of Global magnetic anomaly map EMAG2 (for Google Maps/Earth) at:
http://ngdc.noaa.gov/geomag/data/Google_Maps/EMAG2/index.html

His post is here:
http://groups.google.com/group/maptiler/msg/fe105e27a62711e4

Best regards,

Klokan

On Tue, Mar 31, 2009 at 6:37 PM, Mano Marks <mmarks at google.com> wrote:
> I'm getting started with gdal2tiles, and I'm getting strange results.
>
> I downloaded a blue marble jpg from NASA:
> http://www.nasa.gov/vision/earth/features/blue_marble.html
>
> And I ran the following command lines:
>
> gdal_translate -of VRT -a_srs EPSG:4326 -gcp 0 0 -180 90 -gcp 21600 0
> 180 90 -gcp 21600 10800 180 -90 world_200401.jpg bluemarble1.vrt
>
> gdalwarp -of VRT -t_srs EPSG:4326 bluemarble1.vrt bluemarble2.vrt
>
> gdal2tiles -k bluemarble2.vrt
>
> Of course, the last step took awhile.
>
> The Google Maps and OpenLayers output was fine. However, the KML had
> some odd results. When loaded directly, it looked fine, but when I
> zoomed out, it appeared that what was the equivalent of zoom 0 and 1
> the images retain a Mercator projection. Is this a known issue, or did
> I do something wrong?
>
> --
> Mano Marks
> Geo Developer Advocate
> Google, Inc.
> mmarks at google.com
> http://twitter.com/ManoMarks
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>



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