[Marble-devel] Re: altitude profiles

[Bernhard Beschow]

Am Montag, 27. September 2010, 19:35:29 schrieb Niko Sams:
> On Mon, Sep 27, 2010 at 01:22, Torsten Rahn <torsten.rahn at basyskom.de> wrote:
> > Hi Niko,
> >
> >> And who would run the server that
> >> serves the tiles?
> >
> > Server space is no issue: Just get in touch with dirk at kde.org (Dirk Müller,
> > our KDE Sysadmin).
> >
> > We can use kde.org servers for providing tiles - at least as long as it's
> > about Gigabytes of data.
> ok, I thought that might be not that easy.
> 
> > In fact we do this already for the base imagery (satellite view, srtm, etc).
> where can I find the code for that?
> 
> > Also especially for base data we want full control over the servers. I'm not
> > keen on the idea of downloading stuff from NASA servers where the data
> > suddenly disappears or gets moved elsewhere and we can do nothing about it.
> yeah, that is true of course.
> 
> >> The original SRTM data is in tile files with 1° resolution, with a
> >> filesize of max 2MB
> >> each tile (in my area).
> >
> > 2 MB is unfortunately too big: Think about:
> >
> > * it takes about a minute to download a 2MB file on an average 3G/GPRS
> > connection. That is unacceptable.
> > * We also want to run Marble on phones/tablets/embedded devices.
> > * There should be an efficient way to apply the SRTM data to the imagery tiles
> > (e.g. as surface meshes or via a blending filter for the stacked tiles)
> > * Ideally we'd reuse our own code for managing the chunks of data that are
> > kept in memory (how would this work with the 2MB tiles?).
> Ok, i see your point.
> 
> >
> >> There exists even C++ code for directly
> >> reading those files.
> >
> > That's nice. But I rather see the advantage of that in being able to
> > preprocess the data so that it fits our requirements.
> >
> > Marble is also a Qt library. Code that is integrated with Marble should also
> > get evaluated based on design and API considerations :-)
> My only reason for directly using the existing files it just that I
> don't have to
> think about a new format. Could you give me some hints on where to
> find examples how this could be implemented...

If you're looking for a conversion tool, there is gdal, which should be part of your distribution. To convert a single file, issue:

gdal_translate -ot UInt16 -of GIF SRTM_fB03_n051e013.tif SRTM_fB03_n051e013.gif

Note that converting to PNG didn't deliver correct results for me. Gdal also provides a retiling utility, which I didn't try, though.

Greetings,
Bernhard