[Marble-devel] altitude profiles

[Niko Sams]

Hello,

> You mean a float item? Or a Dialog? Maybe you can make the code generic enough
> so that it can be used for both.
I was thinking of a float item.
>
>> * 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.
I would like to have the best possible resolution.

>>   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.
The original SRTM data is in tile files with 1° resolution, with a
filesize of max 2MB
each tile (in my area). There exists even C++ code for directly
reading those files.


> 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.
agreed, but for that we need to find a good one, or set up our own.

> 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 ...
Do you think 2MB chunks are too large? And who would run the server that
serves the tiles? Imho option 1. should work for us.

>> 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. :-)
good idea.

>
>> 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.
Ok, I will have a look at how this works...

thanks,
Niko