[gdal-dev] Using a gdal generated tiff to generate DEM tiles - losing registration

[Chaitanya kumar CH]

Iain,

Can you provide the code?

On Mon, Oct 31, 2011 at 12:46 AM, Iain <iainmalcolm1 at googlemail.com> wrote:

> I'm building a set of 'tiles' that actually just contain dem data to drive
> a
> 3d geograpic tool on android (using opengl es2.0)
>
> primarily for the uk (cos that's where I am) but hopefully in a way that
> works anywhere.
>
> I've picked up the srtm data and used gdal translate and gdawarp as
> described in the  http://wiki.openstreetmap.org/wiki/HikingBikingMaps
> openstreetmao wiki here , and used these to add height colouring and
> contour
> lines to mapnik generated tiles and this all works well and appears to be
> OK.
>
> To get the 'height' tiles I'm using the same giant tiff that I use as input
> to hill shade and colour-relief to a little home brew app that uses the
> gdal
> library to fetch out a tilesworth of data and then scales it and writes a
> tile file (using the same tile naming scheme as mapnik / tms.  But the
> tiles
> I generate appear to be out about 1/4 degree too far north (look OK east
> west) over the whole area.  (the mapnik generated tiles, using background
> from hill shade + colour-relief and data from openstreetmap in a postgis
> database are all fine and match exactly the position of tiles from the
> openstreetmap server.
>
> I am linearly scaling the raster info using the geo info from the giant
> tiff
> and the  http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames code here
> to translate between tile numbers and lon/lat.
>
> Is linear scaling the wrong way to do this?  (but if so I would expect the
> error to change as I move north - south).
>
> I am considering using gdal2tiles to generate out the tiles, (I think I can
> easily tweak the settings to generate 16bit tiffs, and then reprocess these
> to fix the filenames and reformat the data ready for the android device),
> but this is a rather long way around to get there.
>
> Anyone know why this all goes awry?
>
> --
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-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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