Wednesday, 28 December 2016

Interactive Terrain Mapping in QGIS

During last year's winter break I did a little animation of Arctic sea ice, which eventually ended up being shown in slightly modified format in Svalbard Museum - and they even sent me a nice hat for my efforts. This year's spare time project was to look a bit more at terrain mapping in QGIS, with a purpose. Since I'm a Highlander in exile I dream of the hills quite a lot, and the mountains in particular. If you follow mountain weather reports for the Highlands, you'll hear of fairly regular avalanches. They may not have the ferocity of avalanches elsewhere in the world, but they can be deadly. The Scottish Avalanche Information Service do a great job of recording, documenting, mapping and educating here so I thought I'd add this data to some 3D interactives using Minoru Akagi's Qgis2threejs QGIS plugin and Ordnance Survey Open Data. If that sounds like gobbledygook to you, never mind - just look at the little animation below to see one of the outputs. The red dots are the locations of recorded avalanches since 1991. You can also play around with it in your web browser - it's quite good fun.

Avalanche data is from the Scottish Avalanche Information Service

I extracted the avalanche data from the SAIS webmap and just plotted the locations in QGIS. I decided to focus on an area I know relatively well - the Cairngorm mountain area. It's not high by world standards, at 1,245m/4,085 feet (6th highest in the UK), but at 57 degrees north and nothing much protecting it from the fierce winter weather, conditions up there can be extreme. In fact, I remember growing up sitting many times on the old chairlift as it swung in the wind! Not for the faint hearted. Anyway, as is the way with these things, the area I wanted to look at was split between map tiles, as you can see below in this QGIS screenshot.

I think there must be a name for the law of split map tiles

Methods-wise, I just patched together a few map tiles, clipped out the area I wanted to focus on, overlaid the avalanche location data, generated a hillshade with an azimuth of 180 and elevation of 27 (to simulate shadows at noon on 26 December), and then added some Ordnance Survey map tile data on top of it. I also did a version with Google satellite imagery, just to see what kind of result I could get. I've posted a little gif of the satellite version below, followed by more of the images. You can also play around with a smaller version of this in your web browser. It should also work on phones, but you might have to use three fingers to pan around.

This uses Google satellite imagery - interactive here

What you'll see below in the next five images are just screenshots from the final interactive from my web browser. You should see them in larger size if you click on them. I've modified some of the settings slightly but basically it's quite an easy thing to do in QGIS with the Qgis2threejs plugin. The updated document on this (18 Oct 2016) is also available in a single, handy pdf. If you want to use this tool, you'll find lots of useful tips in here.

Full view of the final interactive - looking north

Focused on Loch Avon (pronounced Loch A'an

This shows the main areas of avalanche activity in one view 

This is a view with the Lairig Ghru pass in the foreground

Another more vertical view of the southern part of the area

I like the effect here with the hillshade layer providing some sense of depth and shadow. There is no vertical exaggeration here and in the interactive version you can zoom in quite far before it becomes pixellated. I also wanted to see what kind of quality I could get by adding in a Google satellite layer and then exporting that. For this, I used the OpenLayers plugin in QGIS (though QuickMapServices is also really good for this). The final version was pretty big as I exported at a high resolution, but here are some snapshots.

The full view of the satellite version - click to enlarge

Loch Etchachan - watch this video!

A different view, showing a cluster of recorded avalanches

The resolution here is actually quite good

This is a view from 'over the back' of the ski area

One final overview image, just for completeness

As I said above, I also did a little extract of this focusing on a smaller area around Loch Avon. The satellite imagery changes part way along the loch but it's still quite pleasing. The interactive version works pretty well in the browser and the image quality here is also pretty good (I exported this at 200% in the Qgis2threejs settings).

Loch Avon - a nice little video from March 2016

It's not always winter here - take a look

Along the way, I almost forgot why I started to map this - the purpose was to plot some interesting and important data on top of the terrain in order to try to understand more about which areas are particularly prone to avalanches. Along the way, I learned more about Mike Spencer's snow hydrology research and PhD (more on that here) and found out some stuff that will help me update my teaching material on this topic. I did begin to look at the Ben Nevis area as well (below), but I decided to focus on the Cairngorms instead this time.

25 years of avalanche locations (red dots) for the Nevis Range

That's all for now. Thanks to the kind of data collected by the SAIS, Ordnance Survey Open Data, and great tools like QGIS and Qgis2threejs, it's becoming much easier to explore, analyse, visualise and understand important datasets. That is kind of what I was attempting here, as a little holiday experiment.

Thanks for reading.

Map data: Contains OS data © Crown copyright and database right 2016