****************************************************************

  lasnoise:

  This tool flags or removes noise points in LAS/LAZ/BIN/ASCII
  files. The tool looks for isolated points according to certain
  criteria that can be modified via '-step 3' and '-isolated 3'
  as needed. The default for step is 4 and for isolated is 5. It
  is possible to specify the xy and the z size of the 27 cells
  separately with '-step_xy 2' and '-step_z 0.3' which would create
  cells of size 2 by 2 by 0.3 units.

  The tool tries to find points that have only few other points
  in their surrounding 3 by 3 by 3 grid of cells with the cell
  the respective point falls into being in the center. The size
  of each of the 27 cells is set with the '-step 5' parameter.
  The maximal number of few other points in the 3 by 3 by 3 grid
  still designating a point as isolated is set with '-isolated 6'.

  By default the noise points are given the classification code
  7 (low or high noise). Using the '-remove_noise' flag will
  instead remove them from the output file. Alternatively with
  the '-classify_as 31' switch a different classification code
  can be selected. Another option is the '-flag_as_withheld'
  switch which sets the withheld flag on the points identified
  as noise.

  It is also important to tell the tool whether the horizontal
  and vertical units are meters (which is assumed by default)
  or '-feet' or '-elevation_feet'. Should the LAS file contain
  proper projection VLRs then there is no need to specify this
  explicitly. Internally the step size in xy or in z direction
  will be multiplied with 3 if the coordinates are found or are
  specified to be in feet. The size of the grid cells needs to
  be changed with '-step 0.0001' or similar if the input is in
  geographic longlat representation.

  You can avoid having certain points being classified, marked
  withheld, or removed with the '-ignore_class 2' option.

  Please license from martin@rapidlasso.com before using lasnoise
  commercially. Please note that the unlicensed version will set
  intensity, gps_time, user data, and point source ID to zero,
  slightly change the LAS point order, and randomly add a tiny
  bit of white noise to the points coordinates once a certain
  number of points in the input file is exceeded.

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

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

  Martin @rapidlasso

****************************************************************

example usage:

>> lasnoise -i tiles\*.laz ^
            -step 2 -isolated 3 ^
            -odix _denoised -olaz ^
            -cores 7

classifies all points that have only 3 or fewer other points in
their surrounding 3 by 3 by 3 grid (with the respective point
in the center cell) where each cell is 2 by 2 by 2 meters in size
as classification code 7.

>> lasnoise -i lidar.las ^
            -remove_noise ^
            -ignore_class 2 ^
            -o lidar_without_noise.laz

removes all points - except those classified as 2 (ground) - that
have only 5 or fewer other points in their surrounding 3 by 3 by 3
grid (with the respective point in the center cell) where each cell
is 4 by 4 by 4 meters in size.

>> lasnoise -i tiles_raw\*.laz ^
            -classify_as 31 ^
            -step_xy 1 -step_z 0.2 -isolated 5 ^
            -odir tiles_denoised\ -olaz ^
            -cores 3

running on whole folder of files on 3 cores where each cell being
only 1 by 1 by 0.2 meters in size and where points that have only
five or fewer other points in the 27 cell neighborhood of their
surrounding 3 by 3 by 3 grid are considered noise. here points
are classified to class 31 instead of being removed.

for more info:

D:\lastools\bin>lasnoise -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
  -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 140301 (unlicensed)
usage:
lasnoise -i in.laz -o out.laz
lasnoise -i raw\*.laz -step 2 -isolated 3 -odir D:\denoised -olaz
lasnoise -i *.laz -step 4 -isolated 5 -olaz -remove_noise
lasnoise -i *.laz -step 3 -isolated 10 -olaz -flag_as_withheld
lasnoise -i tiles\*.laz -step 3 -isolated 3 -classify_as 31 -odir denoised -olaz
lasnoise -h

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