The first principal step of treeseg is to identify the individual trees in the larger-area point cloud. This identification is undertaken on a slice segmented from the larger-area point cloud along the xy-plane. To generate this slice at some defined height above-ground whilst adjusting for topography, it is necessary to construct an underlying digital terrain model (DTM). Both this DTM, and the slice can be generated using:
getdtmslice 2 2.5 3 6 NOU11.tile.downsample.*.pcd > NOU11.dtm.dat
Where the inputs are: 1) the resolution of the DTM (m), 2) the percentile of the z-coordinates of the points inside each DTM grid which is considered to constitute the ground (this is used, rather than the absolute minimum, to provide more robust results in noisy point clouds), 3) the minimum height of the slice above-ground (m), 4) the maximum height of the slice above-ground (m), and 5) the downsampled tiles constituting the larger-area point cloud.
The resulting slice can be viewed using:
pcl_viewer NOU11.slice.pcd
Which will look something similar to:
