In the recent text, I’ve shown you how to get the elevation data to QGIS without DEM. Imagine, that this is a track for equipping any point in QGIS with elevation data regardless of its location on our map. Maybe it’s not that useful when our point layer is restricted to some small area bounded within i.e. 10-20km, but if our points are spread across a whole continent, for example, this method can save a lot of time for you.
The image above shows the situation I would like to describe here. Our layer has massive extents over i.e. a continent. In this case, is rather impossible to execute the elevation data from just one DEM file. These files, in fact easily downloadable are restricted to smaller areas (Pic. 2).
Therefore it’s essential to apply another method, which would allow us to equip all our points with the elevation data without this whole hassle. As per my previous article explaining a very similar issue, we know, that elevation received from the Terrain mode in Google Earth rather not vary that much from the SRTM data utilized by GpsVisualizer.com. So I will stick to this website again, but the way of acquiring the elevation data will be slightly different. Let’s get started!
1. Open the attribute table of your layer and provide the ID number for the description column (Pic. 4). If the column doesn’t exist, create it. If something already exists in this column, move it to the other column (Pic. 1 – 3).
The ID number can be provided simply by the $id expression in the builder (Pic. 4). Afterwards, we will have the unique ID number assigned to every input. We can organize it later, but it’s not necessary.
2. Export your current layer as the .kml file. Make sure, that you’ve chosen the WGS84 system, in which the Keyhole Markup Language operates.
3. Import your file to GpxVisualizer.com, next hit the “Convert & Add Elevation” button making sure, that the .gpx file extension is selected (Pic. 6).
Now we are reaching the moment, where you will understand why creating (or equipping) the description column with a unique ID number was legitimate at the very beginning. This is because we have to match at least one layer of our column with the column created by the converted .gpx file. Because the column name doesn’t represent exclusive data leaving even some items empty across the whole table, we need to define another column with will have these values, and what is most important – will fit the column generated by the .gpx file. In our case, it’s the description column, which after conversion falls as desc retaining all the unique values provided (Pic. 9).
Now, as you might have noticed, the previous description column has been superseded with desc retaining all the unique ID values appropriate to the object (point) name and its elevation provided.
4. Join the Waypoint .gpx layer with the layer you are working on. You can do it by right-clicking on your layer -> Properties -> Joins and in the dock window choose the new .gpx point layer as the joining layer and description as a join and target field. In your .gpx layer, it will be the desc column, but everything is the same there, so it will work. In the joining section, we should choose the ele column which contains the elevation data (Pic. 10).
5. Finally our joined elevation field should correspond to the proper place, defined by the unique ID value (Pic. 11).
The name of the column comes as defined at the joining stage. We can define the Custom Field Name Prefix (Pic. 10), but it’s not necessary. The very last step is saving this layer with joined the ele field as the separate layer and carrying on working on your project.
As you might come to conclusion, downloading the Digital Elevation Model in order to extract the elevation data for our point layer is not a mandatory thing. You can omit this step simply by passing your point layer file via the GPSVisualizer.com tool, which will provide this elevation data for you.
- Terrain analysis in QGIS.html
- Gisgeography.com: 5 Free Global DEM Data Sources
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