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I'm trying to extract wall using the LIDAR. I have tried Fusion, Whitebox, Lastools in Arcgis, Saga and Envi. Those are tools that I can use. The walls I am interested are mainly 1 meter high. Some of them locate in woodland and farmland. The most problem blocked me was shrub. For example, I used 'Bare ground' tool of the softwares I mentioned above. All the wall and shrub were removed. If I worked by other workflow, the shrub will remain and complicate walls. Attached is one of my result:

enter image description here

How to remove shrub and remain wall?

How to convert information of wall into vector data such as polyline?

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    Your shrubs are essentially isolated peaks compared with the ridge networks that your walls comprise. As such, you might invert your DEM by multiplying by -1 (or DEM of difference if that is what the above image is) and perform depression filling, which can help remove the shrubs. Then just multiply the result by -1 again. You might include an area threshold to only identify depressions (peaks) smaller than a certain value. – WhiteboxDev Feb 27 '15 at 14:38
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    @WhiteboxDev - maybe you should post that as the answer. Looks like a decent bit of analysis. – GIS-Jonathan Feb 27 '15 at 17:28
  • what is the accuracy of you point cloud? in an oder way what is the distance betwen two points? – elmo Jun 5 '15 at 13:59
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One approach you should try, if you only want to work with the point cloud is the following:

  • Define bare earth points.
  • Remove them (or exclude them from further analysis).
  • Test what objects are described from the remaining points that have more than one pulse returns. Try first of many, first minus last etc. The idea is that the walls you have are non penetrable from the laser pulse, while shrubs are penetrable, so they will create multiple returns per pulse.
  • Indentify the schrubs and remove the schrub points from point cloud.
  • Only points left are the walls, so you can export them in shp (las2shp from Lastools).
    or
  • Rasterize the walls only point cloud (pixelsize according to post spacing of point cloud).
  • Vectorize the raster (in ArcGIS for example) in order to get your vector wall network.

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