lasplanes

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REHÁNY Nikolett (BKK Közút)

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May 27, 2015, 10:45:05 AM5/27/15
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Hello,

I use lasplanes and test with different parameters to find the most optimal planes.
I found example usage in readme but I don't understand the following options:
-eigen_ratio_smallest
-eigen_ratio_largest
-plane_exclusion
-small_eigen_max
-middle_eigen_min
Could someone explain me what can I set with these?

Regards,
Nikolett

 

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Martin Isenburg

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Jun 4, 2015, 2:37:24 PM6/4/15
to LAStools - efficient command line tools for LIDAR processing
Hello Nikolett,

the lasplanes tool is very special and used only by very few folks. The tool is mainly used by folks that are operating mobile or terrestrial RIEGL scanners and use RiScanPro or RiProcess to align their scans data with tie-planes.

The tool tries to ind sufficiently planar patches of LAS/LAZ points fulfilling a number of user-defineable criteria that are output as simple polygons to SHP or RIEGL's PEF format. The tool was originally designed for generating tie planes to match the point clouds of a mobile scan that suffer from errors in the GPS trajectory to accurate terrestrial scans using clean planar patches that are "seen" without obstruction by both scanners.

The algorithm divides the input into cells that are n by n by n units big. It then performs an eigen value decomposition of the covariance matrix of the points in each cell that has more than the minimal number of points. The three eigenvalues have to pass the small_eigen_max, middle_eigen_min, eigen_ratio_smallest, and eigen_ratio_largest criteria. And the plane of points must be sufficiently thin and formed by sufficiently many points after removing no more than a certain percentage of them. Then a polygon with a maximal number of points enclosing a subset of the points is formed that is checked for having a minimal size and a maximal off-planar standard deviation. The surviving planes are output (optionally only if they are sufficiently far from another).
  
Here what some of the parameters mean:

  -cell_size n                sets cells to size n*n*n
  -cell_size_xyx x y z        sets cells to size x*y*z
  -cell_points min            skip if less than min points
  -small_eigen_max max        skip if smallest eigenvalue > max
  -middle_eigen_min min       skip if middle eigenvalue < min
  -eigen_ratio_smallest r     skip if smallest eigenvalue over sum of all three eigenvalues > r
  -eigen_ratio_largest r      skip if largest eigenvalue over sum of all three eigenvalues > r                  
  -plane_thickness t          skip if points form plane thicker than t
  -plane_exclusion p          skip if more than p % of points had to be excluded to make plane slim
  -plane_points min           skip if plane is formed by less than min points
  -polygon_distance dist      skip if polygon not sufficiently far from others
  -polygon_area a             skip if area formed by points is less than a
  -polygon_points max         simplify polygon to have no more than max points
  -polygon_stddev stddev      skip if standard deviation of polygon points from plane > stddev
  -polygon_name T_123_23      set polygon base name
  -polygon_digits d           set number of digits used to enumerate polygon names

This information will be added to the README file in the next version.

Regards,

Martin @rapidlasso

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