[Marble-devel] altitude profiles

[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.

Best Regards,

Torsten

> Niko
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Torsten Rahn
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