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What is the best workflow to import a roughly 1x1 km area from AHN data (Actueel Hoogtebestand Nederland) into Sketchup Make? My goal is to create contours of existing buildings and structures.

AHN is publicly available height-map of the Netherlands. It available as point cloud or raster data, but raw and terrain only (maaiveld).

Given that a 1x1km area consists of roughly 4,000,000 datapoints, I suspect that the first step is to create mesh with significantly less points (e.g. 100,000 to 400,000) before importing it into Sketchup.

I'm a novice in GIS, and plan to do this workflow only once or twice, so I'm mostly interested in free or donation-ware type of software. Preferably those that can be used on macOS.

I'll list my current solution as a possible answer below, but so far my solutions are not as best as I wanted.

  • I would suggest to add the AHN tag here, but can't do so because of my low reputation on this website. – MacFreek Aug 25 '17 at 12:06
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My first attempt was to download a raster TIFF image from http://esrinl-content.maps.arcgis.com/apps/Embed/index.html?appid=a3dfa5a818174aa787392e461c80f781. Unfortunately, when opening the 500MB images, most points where either #000000 or #FFFFFF, so I could not really use that. There are excellent viewers, along with height maps like https://ahn.arcgisonline.nl/ahnviewer/, so perhaps I just could not find a good source.

My second attempt was to visit http://ahn2.pointclouds.nl/. This data is slightly older (AHN2 from 2008 instead of AHN3 from 2015), but has similar high resolution (0.5 meter), and served my purpose. The websites has a great export function to select and download the region I was interested in. I downloaded two LAZ files with a 4mln and 150,000 point cloud, the later for testing.

I used the free and excellent CloudCompare with this workflow:

  1. Open the LAZ files
  2. Normalize the LAZ points. I used the settings "Quadratic" and "prefer +Z", because I read that the first is good for sharp edges on buildings, and the second good for terrain.
  3. Optionally subsample the point cloud to create a lower density point cloud (hoping that this would result in a smaller mesh in the next step)
  4. Use Poisson Surface Reconstruction to turn the point cloud into a mesh, as explained on the PSR wiki page.
  5. Export the Mesh in STL format (it also supports PLY, OBJ, VTK, OFF and DXF, but Sketchup comes with a free STL importer)
  6. Import the STL into Sketchup using the Sketchup STL importer.
  7. Wait till it is imported, and scale it up by a factor 1000x (the imported group was only a centimeter large in the model. I used the "Zoom to selection" function to find it :) )

This worked reasonably well for the sample export (170,000 points translated to 130,000 faces). It will not work for the 4,000,000 point export. Unfortunately, the subsampling resulted in a slightly larger mesh size (150,000 faces), not smaller, and I can't find a way for CloudCompare to reduce the complexity of the Mesh model. An alternative is to hand-pick points, and export that point list, but that seems rather tedious.

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