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I have the following process for automatically creating building outlines/footprints from Las files and was wondering if anyone can help improve it or has suggestions for other processes to use?


A. ArcGIS - Lidardataset tools : while you can see just the building class points you can not create polygon automatically. There is the minimum bounding geometry but as it looks at the dataset as a whole it requires you to manually choose the points for each building.

B. External Lidar Analysis tool by Overwatch - building extraction is a core functionality. http://www.featureanalyst.com/lidar_analyst.htm It took approx 8 minutes to create a bare earth (essential) and then extract the buildings. It gives the best results by far, even capturing building under the trees (1&4). This is without even looking at a tutorial as it is a very intuitive interface.

enter image description here

Some issues are it has missed the covered corridors (3) but has correctly left out the open roof (2).

C. LASTOOLS - used lasmerge to merge 4 relevant tiles and then lasclip to extract zone of AOI only.

arcpy.lasboundary("AOI.las","1","buildings","true","true","shp","AOI_buildings.shp","","#","true") enter image description here

The output was very jagged so I used # arcpy.SimplifyBuilding_cartography("AOI","AOI_buildings_simplified.shp","4 Meters","0 SquareMeters","NO_CHECK") enter image description here

and then ran

arcpy.SimplifyPolygon_cartography("AOI_buildings_simplified","AOI_s.shp","POINT_REMOVE","1 Meters","0 SquareMeters","NO_CHECK","KEEP_COLLAPSED_POINTS") enter image description here 1 and 2 show the issue areas. Part of it is due to bad lidar classification.

This gives good building lines for long straight edged buildings but if there is overlap by branches or it is a complex building with multiple edges, roofs on multiple levels close to each other etc, manual creation is necersary for any detailed site level work. For general estimation roof shape the process is accurate enough. Process takes less than 10mins total once the process has been finalized.

My Research: http://stackoverflow.com/questions/5037588/simplified-or-smooth-polygons-that-contain-the-original-detailed-polygon and the process suggested by @gromix and Concave Hull: Definition, Algorithms and Practical Solutions

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That looks pretty good George. I did something similar a few months back. As you can see, you run into a classification limitation with las tools.....

I'd be interested to see your output from the feature analyst for comparison.

As far as making it better, you can't. That is unless you can classify the points more correctly... Here is a link to an interesting article on overhanging tree classification. http://www.lidarnews.com/content/view/9130/

I wish there was more control within las tools besides standard deviation and height for point classification...

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Thanks Thad. Lidar Analyst was incredibly good. Hope it is not to expensive! –  GeorgeC Aug 15 '12 at 3:23
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