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When I try to use lasheight with -replace z to normalize the point cloud, the height of points are changed (destroyed heights; see pictures below).

Without using -replace z everything is ok, but the normalized point cloud isn't obtained.

no -replace z with -replace z

  • The No. of points ~ 10,000,000. – Abbas Moradi Jul 24 '16 at 5:31
  • The coordinate system is utm, and the datum is WGS84. – Abbas Moradi Jul 24 '16 at 5:32
  • I use QGIS Nødebo 2.16, with "-replace_z". – Abbas Moradi Jul 24 '16 at 5:34
  • I use: lasground, and then: lasheight (an unclassified point cloud without any raster model). – Abbas Moradi Jul 24 '16 at 5:36
  • Considering the input file is an unclassified point cloud, and that you used lasground to generate a ground.las (i.e., a point cloud with only ground points); then use example 2 from my answer. – Andre Silva Jul 24 '16 at 15:29
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Note the correct notation is -replace_z with an underline "_" before z (not -replace z).

Certify what you are using as the reference for normalization; i.e.; you need something to subtract from the point's elevation: usually a DTM (raster), but lasheight will accept the own point cloud if it is already classified regarding ground points (class = 2), or a separate .las file having only ground points.

That being said, the argument -replace_z is not designed to solely normalize the point cloud, but to replace permanently the elevation values for heights in the input file, i.e., the original file. Take a careful read in the lasheight README for more info.

Also, make sure you point cloud is in a projected coordinate system, such as an UTM projection.


Examples, using -replace_z:

If the point cloud is already classified, including ground points:

lasheight -i *.las -replace_z.

If it is not classified, but there is a separate .las file having only ground points:

lasheight -i *.las -ground_points ground.las -replace_z

If it is not classified, the ground truth is a DTM (raster) instead of point data:

lasheight -i *.las -ground_points dtm.asc -replace_z

In the last example, it will also support other raster formats such as .csv, .bil, .txt.

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Besides adding the ground reference for normalizing the point cloud, there were other issues I had to address. They were:

  • bad scale factors x y z: 0.000000335839844, 0.000000499992188, 0.000000037939995 and bad offsets x y z: 31515000, 5686500, 42.900001525878906 of points, where scale factors had sub centimeter resolution.

So, before normalizing, I had to use the following command:

las2las -i input.las -rescale 0.01 0.01 0.01 -auto_reoffset -o fixed.laz

In the LAStools Google Group I posted more details about my LiDAR input file, and the full discussion until its resolution can be accessed here.

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