GIS Blog

Eye Popping Details from LiDAR Data

This post covers some of the amazing detail contained in newish LiDAR-derived DEMs for Canterbury.

LiDAR has popped up in many posts here – and rightfully so.  It’s not too much of an overstatement that these data are revolutionising terrain analysis.  I thought it might be enlightening to show some of that detail from a recently available high-resolution DEM.  Below is an image that shows the extent of a 1 m LiDAR-derived DEM covering a significant area around Lincoln and Rolleston:

Elevations in this DEM range from -1.38 m.a.s.l. up to 118.74 m.a.s.l. (the negative values are close to Te Waihora/Lake Ellesmere and are associated with river beds and races so may be affected by water).  Shading like this doesn’t tell us as much as looking at a hillshade version, shown below:

Okay, so that’s not exactly spectacular, but, trust me, it will be when we zoom in on specific features.  We’ll take a bit of a tiki tour around this DEM, starting around the university:

It’s important to note that this is a “bare earth” DEM, meaning that it’s only got data on the land surface and doesn’t take into account things like buildings and trees.  Off to the east are some of the drainage basins as part of the new subdivisions.  In the image above we can also make out the berms around the Bert Sutcliffe oval.  What about those features just south of the oval?

Walkers around campus will recognise this south eastern corner of the place, where there’s an area of cut and fill:

Notice how we can also make out some the experimental crops to the northeast.  Just to the east we can make out the LII snaking through Lincoln township:

And here’s the aerial:

Further afield, near Prebbleton, we find this:

Looks fairly industrial – and a lowland stream meandering it’s way around nearby.  Looking at the topo map, there’s not much to be seen, though it does note a gravel pit:

The aerial shows us what’s there:

Indeed, it’s a quarry, and less developed in the image than what the LiDAR data show.  Google Map’s image is a bit more up to date:

Let’s zoom in a bit more to compare the detail:

That’s a stunning amount of detail, especially when you consider that even five years ago, the best we could hope for was our national 25 m DEM.  Interestingly, I can’t find any named stream in that area, but clearly something’s there.  It could well be that it’s a remnant of an older, dried up stream (there are several races nearby, for what it’s worth).

Here’s the riverbed of the Selwyn, just west of Coes Ford:

Fantastic stuff – old river channels are clearly visible as are some terraces.  Here’s the aerial of the same area:

In reality, the river is quite constrained here – but the LiDAR data clearly show the subtle traces of where it once was.  The image below shows Coes Ford – the stopbanks are clearly visible:

Last thing we’ll look at – is it aliens?  Ancient geoglyphs?

No, it’s just a centre pivot…

It’s important to note that the datasets are literally snapshots in time and are invaluable for a number of reasons, including providing unprecedented levels of detail for a range of analyses.  Hopefully we’ll be able to report back on some of those in later posts.  Over the summer we’ll be working to make more of these datasets available – they do take up quite a lot of space, but stay tuned.

C

 

• October 12, 2018


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