Iain,<br><br>Can you provide the code?<br><br><div class="gmail_quote">On Mon, Oct 31, 2011 at 12:46 AM, Iain <span dir="ltr"><<a href="mailto:iainmalcolm1@googlemail.com">iainmalcolm1@googlemail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">I'm building a set of 'tiles' that actually just contain dem data to drive a<br>
3d geograpic tool on android (using opengl es2.0)<br>
<br>
primarily for the uk (cos that's where I am) but hopefully in a way that<br>
works anywhere.<br>
<br>
I've picked up the srtm data and used gdal translate and gdawarp as<br>
described in the <a href="http://wiki.openstreetmap.org/wiki/HikingBikingMaps" target="_blank">http://wiki.openstreetmap.org/wiki/HikingBikingMaps</a><br>
openstreetmao wiki here , and used these to add height colouring and contour<br>
lines to mapnik generated tiles and this all works well and appears to be<br>
OK.<br>
<br>
To get the 'height' tiles I'm using the same giant tiff that I use as input<br>
to hill shade and colour-relief to a little home brew app that uses the gdal<br>
library to fetch out a tilesworth of data and then scales it and writes a<br>
tile file (using the same tile naming scheme as mapnik / tms. But the tiles<br>
I generate appear to be out about 1/4 degree too far north (look OK east<br>
west) over the whole area. (the mapnik generated tiles, using background<br>
from hill shade + colour-relief and data from openstreetmap in a postgis<br>
database are all fine and match exactly the position of tiles from the<br>
openstreetmap server.<br>
<br>
I am linearly scaling the raster info using the geo info from the giant tiff<br>
and the <a href="http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames" target="_blank">http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames</a> code here<br>
to translate between tile numbers and lon/lat.<br>
<br>
Is linear scaling the wrong way to do this? (but if so I would expect the<br>
error to change as I move north - south).<br>
<br>
I am considering using gdal2tiles to generate out the tiles, (I think I can<br>
easily tweak the settings to generate 16bit tiffs, and then reprocess these<br>
to fix the filenames and reformat the data ready for the android device),<br>
but this is a rather long way around to get there.<br>
<br>
Anyone know why this all goes awry?<br>
<font color="#888888"><br>
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</font></blockquote></div><br><br clear="all"><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br><br>+91-9494447584<br>17.2416N 80.1426E<br>