The Wrong Side of my Car

A blog about Auckland City, its streets, and culture shock

9 Aug 2017

1m DEM

Last time, one of the questions was, which digital elevation model (or DEM) should I use. Initially I worked with the relatively low-resolution DEM derived from the 20m contour lines.

Of course, Auckland Council has had a 1m DEM derived from lidar data for a while. There’s also a digital surface model, which doesn’t follow the ground level, but which models the ‘surface’ visible from above. You’ll see the buildings and tree tops on that one.

A HDR 1m DEM is a lot of data, but to give it a try I downloaded an area around Birkenhead, which has a good amount of relief.

Here’s a crop from that previous map, using the 15m DEM *1:

Here’s the same crop, using the 1m DEM: *2

That’s a lot more detail, which is expected as it was built using a lot more data. This level of detail is only available in urban areas, while the 15m model covers all of New Zealand.

Both maps clearly show why this area has this weird street grid. It’s simply the only possibility given the relief. And also, riding a bicycle over there is quite miserable.


(*1) 

University of Otago - National School of Surveying — Columbus, J.; Sirguey, P. & Tenzer, R. (2011), ‘A free, fully assessed 15-m DEM for New Zealand’, Survey Quarterly 66, 16–19.

(*2) 

Auckland Lidar 1m DEM (2013), Copyright in the underlying dataset from which this work has been derived is owned by Auckland Council

Contains data sourced from Land Information New Zealand and Landcare Research under CC-BY.

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