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  lastrack:

  This tool takes one (or many) LAS or LAZ files together with
  a trajectory file that must have matching GPS time stamps. It
  then computes the height of each point above this trajectory
  plus a constant offset. This '-offset -1.93' parameter allows
  to subtract the elevation of the GPS unit above the ground for
  a mobile survey by lowering (or raising) the trajectory to be
  at the level of the road surface.

  Is is important that both - the files with the LiDAR points
  the files with the trajectory points - do not only have the
  same GPS time stamps but are also in the same projection.
   
  Should the input coordinates be in some representation where
  the z-axis does not correspond to elevation, such as in an
  earth-centered representation, then all the files need to be
  converted to, for example, a UTM projection first.

  Commonly this is used with switches '-classify_below -0.4 7'
  which classifies all points that are 40 centimeter or lower
  than track (plus offset) as point class 7 (low noise). Similar
  options are '-classify_between -0.4 0.5 2' classifying all
  points between 40 below and 50 centimeter above the track
  (plus offset) as point class 2 (ground). The corresponding
  option '-classify_below 37.5 25' also exists.

  Alternatively you can '-replace_z' the original elevation value
  of each point with the computed height. That means all points
  will have an elevation that equals their height above (or below)
  the track (plus offset). This will "normalize" the elevations of
  the points in respect to the recorded trajectory.

  Another alternative is to use the computed height to eliminate
  points with a particular height above or below a threshold with
  options '-drop_below 1.5' or '-drop_above 6.8'. 
 
  Please license from martin.isenburg@rapidlasso.com before using
  lastrack commercially.

  For updates check the website or join the LAStools mailing list.

  http://lastools.org/
  http://groups.google.com/group/lastools/
  http://twitter.com/lastools/
  http://facebook.com/lastools/
  http://linkedin.com/groups?gid=4408378

  Martin @lastools

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example usage:

>> lastrack -i *.las ^
            -track track.laz ^
            -offset -2.12 ^
            -drop_below -1.2 ^
            -odix _cleaned -olaz

computes for all points from the LAS files that match '*.las' the
heights above their by 2.12 meters lowered trajectory provided as
file 'track.laz' and drops all points whose height is below -1.20 
and stores them with an appendix '_cleaned' as compressed LAZ.


>> lastrack -i tj0012\*.laz ^
            -track tj0012.laz ^
            -offset -2.47 ^
            -classify_below -0.4 7 ^
            -classify_between -0.4 0.5 2 ^
            -classify_between 3 10 25 ^
            -odix _classed -olaz

computes for all points from the LAZ files matching 'tj0012\*.laz'
the heights above their by 2.47 meters lowered trajectory provided
as file 'tj0012.laz' and classifies points whose height is below
-0.40 as 7, all points whose height is between -0.40 as 0.50 as 2,
and all points whose height is between 3.00 as 10.00 as 25 and
stores them with an appendix '_classed' as compressed LAZ.

>> lastrack -i session017\*.laz ^
            -track s017.laz ^
            -offset -1.84 ^
            -replace_z ^
            -odir session017_norm -odix _normalized -olaz

computes for all points from LAZ files matching 'session017\*.laz'
the heights above their by 1.84 meters lowered trajectory provided
as file 's017.laz', normalizes the points by replacing their z
values with with this height, and then stores them with appendix
'_normalized' as compressed LAZ into directory 'session017_norm'.

for more info:

D:\lastools\bin>lastrack -h
Filter points based on their coordinates.
  -keep_tile 631000 4834000 1000 (ll_x ll_y size)
  -keep_circle 630250.00 4834750.00 100 (x y radius)
  -keep_xy 630000 4834000 631000 4836000 (min_x min_y max_x max_y)
  -drop_xy 630000 4834000 631000 4836000 (min_x min_y max_x max_y)
  -keep_x 631500.50 631501.00 (min_x max_x)
  -drop_x 631500.50 631501.00 (min_x max_x)
  -drop_x_below 630000.50 (min_x)
  -drop_x_above 630500.50 (max_x)
  -keep_y 4834500.25 4834550.25 (min_y max_y)
  -drop_y 4834500.25 4834550.25 (min_y max_y)
  -drop_y_below 4834500.25 (min_y)
  -drop_y_above 4836000.75 (max_y)
  -keep_z 11.125 130.725 (min_z max_z)
  -drop_z 11.125 130.725 (min_z max_z)
  -drop_z_below 11.125 (min_z)
  -drop_z_above 130.725 (max_z)
  -keep_xyz 620000 4830000 100 621000 4831000 200 (min_x min_y min_z max_x max_y max_z)
  -drop_xyz 620000 4830000 100 621000 4831000 200 (min_x min_y min_z max_x max_y max_z)
Filter points based on their return number.
  -first_only -keep_first -drop_first
  -last_only -keep_last -drop_last
  -keep_middle -drop_middle
  -keep_return 1 2 3
  -drop_return 3 4
  -keep_single -drop_single
  -keep_double -drop_double
  -keep_triple -drop_triple
  -keep_quadruple -drop_quadruple
  -keep_quintuple -drop_quintuple
Filter points based on the scanline flags.
  -drop_scan_direction 0
  -scan_direction_change_only
  -edge_of_flight_line_only
Filter points based on their intensity.
  -keep_intensity 20 380
  -drop_intensity_below 20
  -drop_intensity_above 380
  -drop_intensity_between 4000 5000
Filter points based on their classification.
  -keep_class 1 3 7
  -drop_class 4 2
  -drop_synthetic -keep_synthetic
  -drop_keypoint -keep_keypoint
  -drop_withheld -keep_withheld
Filter points based on their user data.
  -keep_user_data 1
  -drop_user_data 255
  -keep_user_data_between 10 20
  -drop_user_data_below 1
  -drop_user_data_above 100
  -drop_user_data_between 10 40
Filter points based on their point source ID.
  -keep_point_source 3
  -keep_point_source_between 2 6
  -drop_point_source 27
  -drop_point_source_below 6
  -drop_point_source_above 15
  -drop_point_source_between 17 21
Filter points based on their scan angle.
  -keep_scan_angle -15 15
  -drop_abs_scan_angle_above 15
  -drop_scan_angle_below -15
  -drop_scan_angle_above 15
  -drop_scan_angle_between -25 -23
Filter points based on their gps time.
  -keep_gps_time 11.125 130.725
  -drop_gps_time_below 11.125
  -drop_gps_time_above 130.725
  -drop_gps_time_between 22.0 48.0
Filter points based on their wavepacket.
  -keep_wavepacket 0
  -drop_wavepacket 3
Filter points with simple thinning.
  -keep_every_nth 2
  -keep_random_fraction 0.1
  -thin_with_grid 1.0
Transform coordinates.
  -translate_x -2.5
  -scale_z 0.3048
  -rotate_xy 15.0 620000 4100000 (angle + origin)
  -translate_xyz 0.5 0.5 0
  -translate_then_scale_y -0.5 1.001
  -switch_x_y -switch_x_z -switch_y_z
  -clamp_z_below 70.5
  -clamp_z 70.5 72.5
Transform raw xyz integers.
  -translate_raw_z 20
  -translate_raw_xyz 1 1 0
  -clamp_raw_z 500 800
Transform intensity.
  -scale_intensity 2.5
  -translate_intensity 50
  -translate_then_scale_intensity 0.5 3.1
  -clamp_intensity 0 255
  -clamp_intensity_above 255
Transform scan_angle.
  -scale_scan_angle 1.944445
  -translate_scan_angle -5
  -translate_then_scale_scan_angle -0.5 2.1
Change the return number or return count of points.
  -repair_zero_returns
  -set_return_number 1
  -change_return_number_from_to 2 1
  -set_number_of_returns 2
  -change_number_of_returns_from_to 0 2
Modify the classification.
  -set_classification 2
  -change_classification_from_to 2 4
  -classify_z_below_as -5.0 7
  -classify_z_above_as 70.0 7
  -classify_z_between_as 2.0 5.0 4
  -classify_intensity_above_as 200 9
  -classify_intensity_below_as 30 11
Modify the user data.
  -set_user_data 0
  -change_user_data_from_to 23 26
Modify the point source ID.
  -set_point_source 500
  -change_point_source_from_to 1023 1024
  -quantize_Z_into_point_source 200
Transform gps_time.
  -translate_gps_time 40.50
  -adjusted_to_week
  -week_to_adjusted 1671
Transform RGB colors.
  -scale_rgb_down (by 256)
  -scale_rgb_up (by 256)
Supported LAS Inputs
  -i lidar.las
  -i lidar.laz
  -i lidar1.las lidar2.las lidar3.las -merged
  -i *.las - merged
  -i flight0??.laz flight1??.laz
  -i terrasolid.bin
  -i esri.shp
  -i nasa.qi
  -i lidar.txt -iparse xyzti -iskip 2 (on-the-fly from ASCII)
  -i lidar.txt -iparse xyzi -itranslate_intensity 1024
  -lof file_list.txt
  -stdin (pipe from stdin)
  -rescale 0.01 0.01 0.001
  -rescale_xy 0.01 0.01
  -rescale_z 0.01
  -reoffset 600000 4000000 0
Supported LAS Outputs
  -o lidar.las
  -o lidar.laz
  -o xyzta.txt -oparse xyzta (on-the-fly to ASCII)
  -o terrasolid.bin
  -o nasa.qi
  -odir C:\data\ground (specify output directory)
  -odix _classified (specify file name appendix)
  -ocut 2 (cut the last two characters from name)
  -olas -olaz -otxt -obin -oqfit (specify format)
  -stdout (pipe to stdout)
  -nil    (pipe to NULL)
LAStools (by martin@rapidlasso.com) version 140527 (academic)
usage:
lastrack -i in.laz -track tj.laz -offset -2.21 -o out.laz
lastrack -i in.laz -track tj.laz -o out.laz -v
lastrack -license
lastrack -version
lastrack -h

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if you find bugs let me (martin.isenburg@rapidlasso.com) know.
