DTM troubleshooting for Spatial Scientific

DTM testing
Two great looking DTMS – which one is problematic? and why?

My first job as a new consultancy! In August 2013 I was asked to solve a DTM problem for a local airborne surveying company, Spatial Scientific.

Starting with two collections of ASCII points at different spatial resolution and an orthophoto, my job was to find out which DTM was ‘right’ – or free of unusual artifacts. Given the initial data format, my first instinct is to treat them as point clouds. In this case CloudCompare is the first port of call, and showed a clear pattern of artifacts present when the DTMs were compared. This exercise gave me a spatial context for the DTM issues – but when the gridded DTM points are 3 to 10m apart and the DTM differences are in the order of decimetres, it is very hard to tell where exactly the artifacts come from.

The solution came in the form of an image analysis approach. Initial concerns about the DTMs came from a raster DTM differencing process, so I first reproduced this result using the rasterised ASCII data. Again, this alone did not provide any clues about which DTM was at fault.

It was impossible to detect the DTM problems by close examination, and difficult to know which DTM was the issue by comparison. So I enlisted the help of image processing methods. Detecting edges and slopes in each DTM clearly identified the culprit – edges and steep slopes/steps leaping from the screen where none should exist! Combined with the CloudCompare result, it gave a very clear picture of where the DTM had problems and pointed clearly at the source. Problem solved.

Tools used: Cloudcompare; QGIS; Sextante; GDAL_translate; GMT

Acquiring prism lock: the cover photo

The cover photo for this site shows.. the back of my head, a Leica Viva TS 15, a prism, and a bright yellow, low cost, very effective instrument warming/battery box I’m very proud of! I’m acquiring prism lock using the remote control, before heading out to collect locations on a SIPEX II ice station. The sea ice surveying project was part of my work for the Australian Antarctic Division, and complements my PhD studies. It was a challenging task – nobody knew if the total station would play happily at -20 degrees celcius on drifting sea ice. It performed admirably, and the results will provide much-needed spatial glue for on, over and under ice spatial datasets collected on the voyage. Photo: Polly Alexander

Spatialised is born

Hi everyone, and welcome to Spatialised! – a consultancy aimed at solving spatial analysis, problems.

I can help you with point cloud analysis and manipulation, photogrammetric modelling methods, airborne LiDAR problem solving, DTM, DEM and DSM production. See my toolkit page for an up-to-date list of my in-house capacity and what I can do using your software and hardware.

With experience drawn from four reseach voyages to the Antarctic pack ice zone, I can also offer logistical and OH & S support for data collection in remote areas.

I’m currently based in Adelaide, South Australia – I’m happy to work locally or for remote clients anywhere in the world. I hope I can help you solve your spatial problems.

Interesting spatial discoveries, news and updates will appear here as they come – you’ll find links to contact information, a bit about myself and my spatial toolkit in the menu bar above.

Happy trails!