[Marble-devel] altitude profiles

[Bernhard Beschow]

Hi,

Am Sonntag, 26. September 2010, 16:17:33 schrieb Torsten Rahn:
> Hi,
> 
> Great that you want to look into this.
> Here are a few thoughts by me:
> 
> Am Sonntag, 26. September 2010 11:48:12 schrieb Niko Sams:
> > Hi,
> > 
> > I'd like to implement altitude profiles and would like to do a bit of
> > brainstorming beforehand.
> > 
> > * it should be an overlay widget showing the graph
> 
> You mean a float item? Or a Dialog? Maybe you can make the code generic enough 
> so that it can be used for both.
> 
> > * it should read data either from a GPX file (if avaliable) or use
> > locally avaliable SRTM data.
> 
> Well, the atlas theme is currently using a very coarse srtm data set already 
> (encoded as a grayscale image). This SRTM dataset was actually created using 
> GMT mapping tool.
> 
> >   using a webservice might also be an option, but I haven't found a good
> > one yet * it should calculate statistics like total incline/decline
> > * it should be available for opened tracks and routing tracks
> 
> There are basically three options for implementing this feature:
> 
> 1.) Ask the user to download huge chunks of SRTM data in advance and then run 
> some code over it which figures out the height profile. This is certainly the 
> worst idea and I wouldn't want to see this in Marble since it's not the way 
> that Marble users are supposed to interact with data. We already do this 
> approach with offline routing. And the only reason that we accept this 
> approach there is the complexity of retrieving chunks of data that can be used 
> offline to determine a good route.
> 
> 2.) Use a webservice. This is probably the easiest approach and a good 
> temporary solution. I guess this one would be the best option for now.
> 
> 3.) Use tile data: This is an approach that we have to take in the future to 
> render 3D surfaces anyways: The DEM/SRTM data should get tiled in a tile 
> layout and should be downloaded seemlessly like the image data. 
> One possible option would be to demand the same tile layout for the srtm data 
> as for the imagery, so that it could be stored as part of  a StackedTile. 
> Another option would be to have it downloaded in a tile layout that is 
> different from the one used for the various map themes. I guess the latter 
> option would make most sense ... 
> 
> > UI issues:
> > Where to choose the track to display?
> > - gpx files can contain multiple tracks, currently all are shown
> > - what happens if a track is opened and a route is shown
> > Maybe a combobox where the track can be choosen
> 
> I think it would also be cool if the feature worked together with the measure 
> tool to get more accurate measurements. :-)
>  
> > Implementation issues:
> > * a new plugin that adds a info box like Routing does
> > * data available in the track can be read from GeoDataCoordinates and
> > displayed * where to store altitudes that the plugin needs to figure out
> > itself?
> 
> See above. I guess it would be cool if eventually we'd store the srtm data in 
> the map data directory as tiles. Currently we are kind of doing this already 
> for the Atlas theme which contains coarse SRTM data already.

For the OpenGL mode, I need a high-bandwidth solution which delivers height information for arbitrary geo coordinates. Perhaps we should have a deeper look into option #3?

Greetings,
Bernhard