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I have some GPX files which have elevation data, but I am aiming for greater accuracy. Currently I have used OS benchmarks to correct the barometric elevation data. Online digital elevation models (ASTER, SRTM, Strava, etc) do not provide the degree of precision or accuracy that I was seeking and perform more poorly than the barometric data.

I have downloaded QGIS, imported a shape file as a layer from the Environment Agency (UK) and imported a GPX route. Unfortunately the shape file appears, as I suspected, to be just the areas covered by the LIDAR and not the actual elevation data.

It seems I am stuck at a most basic level.

Also, later I would actually like to be able to draw a GPX route and get elevation data from the LIDAR dataset and export as GPX.

Is this possible do you think?

I would like to be able to access much of the data linked to on this page: https://www.researchgate.net/post/Which_EU_Countries_provide_free_access_to_LIDAR_data_files_in_2017 and more if available.

I have got to here:

enter image description here

But I am really struggling to see how to get the elevation assigned to the GPX despite the link in the answer below. (and to export gpx when that is done).

PolyGeo
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Jonathan
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    Welcome to GIS Stack Exchange! There are many ways to do what you want. Most involve using an elevation raster (which you could derive from the lidar) from which GIS software can assign elevation values to your point feature. A similar question answered here: https://gis.stackexchange.com/a/317241/24989 – cm1 May 15 '20 at 12:38

1 Answers1

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I have figured this out using the tip and link above.

For UK Environment Data go here: https://environment.data.gov.uk/DefraDataDownload/?Mode=survey For US data go to https://opentopography.org/

Choose the DSM (surface model includes buildings) or DTM model (terrain only).

Very important - ensure QGIS is set to the Coordinate Reference System that you are about to use (e.g. for UK Environment Agency Data this is EPSG 27700 - OSGB / British National Grid)

Download the data, unzip and drag the arc files or GeoTiff files into QGIS

Merge them.

If you hillshade that layer you can see where the track runs off the path

Right click your GPX layer and Export>Save Features as. Choose ESRI shapefile. Very important - Choose the coordinate reference system of your DEM. You can modify the points on this file in QGIS to ensure the GPX runs along the route you want.

Then use SAGA Add raster values to points for the shapefile layer

Right click the new layer and choose Open attribute table. Then click the abacus symbol and update existing field (ele) and in the formula box type the name of your DEM layer. Save.

Then right click the shapefile layer and export as GPS. Set use extensions to True. Set Force GPX track to True. Set Geometry type to points.

I have made a video here: https://youtu.be/mqDgOfTQnXs

PolyGeo
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jonathanc
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