[Marble-devel] Questions About Marble Installation

[Torsten Rahn]

Hi Paul,

On Wednesday 21 April 2010 23:34:41 Paul Carlisle wrote:
> We will very likely be using Marble for an upcoming project that requires
> the display of a user's position on a map. Resolution will never have to
> be very high - at the finest, we probably won't have to show an area any
> smaller than roughly 50 miles on a side. The application will be written
> in C++ using Qt and the MarbleWidget class, running under Unix.

Great :-)
 
> Unfortunately, this application will almost never have Internet access, so
> we will be forced to provide a large image, or our own set of image tiles.

Yes, that would both be possible.
 
> After playing with a simple demo program, I note that the Blue Marble
> dataset only seems to contain a single JPEG image that is 2700x1350
> pixels. This seems awfully small for the level of detail seen in the
> zooms. Is it drawing the data from somewhere other than the <install
> location>/data directory? Or is Marble just using a really good scaling
> algorithm?

Marble is fetching more tiles from the internet while you are browsing the map. 
The data is downloaded to ~/.marble/data by default in all versions up to 0.9.x.

So I guess you have an internet connection running in the background which 
downloads the data behind your back (it's possible to disable this behaviour 
btw., so that Marble remains in offline mode). :-)

> I note in your documentation that the largest image that the widget will
> automatically tile is 10800x5400. If we choose to download, say, the full-
> resolution NASA Blue Marble images and provide our own tiles, is it
> sufficient to simply place the tile directly tree in the data area, or are
> there additional steps needed to make the application locate the tiles?
 
There are no further steps necessary. :-) You can just place the downloaded 
tiles either in the local ( ~/.marble/data ) or system/install directory. 

> Also, what is the recommended way of telling Marble where the data is
> stored? 

Yes, see the third chapter at:
http://edu.kde.org/marble/obtain.php

> Is there an environment variable, or can the path be set at
> runtime? I'm referring to the widget, not the Marble executable.

Yes, see the third chapter at:
http://edu.kde.org/marble/obtain.php

You might also have a look at the documentation of the MarbleDirs class for a 
better understanding :-)

Note also that this stuff has changed in trunk. For development we usually 
recommend to use the stable Marble version (i.e. right now this is 0.9.x).
But if you should decide to use trunk then you need to be aware of the recent 
changes (which Bastian could tell more about). 

> We will
> likely not be given root access when we install our application and data,
> so we need to be able to configure Marble to look where we will be forced
> to install.
> 
> If this project succeeds, we may explore the possibility of building our
> own Open Street Map server in order to provide the follow-on level of
> detail some users will want. 

That should work fine with Marble as well. 

> For now, however, high-resolution imagery
> will probably be sufficient.

Cool,

Best Regards,

Torsten

> 
> Thank you in advance for your help.
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