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  lasoverlap:

  This tool reads LIDAR points from LAS/LAZ/ASCII/BIN/SHP and
  checks the flight line overlap and / or the vertical and
  horizontal alignment.

  The most important parameter '-step n' specifies the n x n
  area that of LiDAR points that are gridded on one raster
  (or pixel) that are then used for doing the overlap and/or
  difference calculations. The output is either in BIL, ASC,
  IMG, TIF, PNG, JPG, XYZ,or DTM format. When computing the
  difference in the flight line overlaps, by default the tool
  will check '-elevation_lowest', but '-intensity_highest', or
  '-counter' are possible too.

  When the input are already tiled flightlines that do not have
  flight line information in the point source ID then the option
  '-recover_flightlines' may be useful that tries to use the GPS
  time stamp of each point to resolve which points are from the
  same flightline.

  Optionally, a KML file is generated that allows the resulting
  raster  to be immediately displayed inside a geospatial context
  provided by Google Earth (for TIF/PNG/JPG images). In case the
  LAS/LAZ file contains projection information (i.e. geo keys
  as variable length records) this metadata is used to correctly
  geo-reference the KML file. It is also possible to provide the
  proper geo-referencing information in the command-line.

  Use '-subsample n' with 1 < n < 5 to anti-alias the gridding of
  LiDAR points by their x and y coordinate into disjunct rasters.
  The option '-subsample 3' adds each LiDAR point 9 times to the
  raster at locations (x/y), (x+0.33*step/y), (x+0.66*step/y),
  (x/y+0.33*step) (x+0.33*step/y+0.33*step) (x+0.66*step/y+0.33*step),
  (x/y+0.66*step) (x+0.33*step/y+0.66*step) (x+0.66*step/y+0.66*step)
  and thereby "washes out" hard boundaries.

  Please license from martin.isenburg@rapidlasso.com to use lasoverlap
  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:

>> lasoverlap -i tile.las -step 2

creates an overlap raster as well as a difference raster with a
step of 2 units. For this, it is necessary that the LiDAR points
in the LAS file have their point source ID populated with the
flight line ID. The overlap raster uses the default color ramp
which maps overlap counts from 0 to 5 to a different colors. The
difference raster uses the default color ramp that maps blue to
-2.5, white to 0, and red to 2.5. The default output is PNG.

>> lasoverlap -i tile.las -step 2 -values -oasc

same as above but output the actual values into an ASC raster
(instead of the color-coded values into a PNG).

>> lasoverlap -i tile.las -step 2 -values -oasc -recover_flightlines

same as above for the case the tile does not have proper information 
in the point source ID field but has valid GPS time stamps. The GPS
time stamps are then used to recover the flight line information by
looking for continous segments (or rather interruptions) in the GPS
time stamps.

>> lasoverlap -i LDR*.las -files_are_flightlines -step 3 -max_diff 2

merges all the files "LDR*.las" while assigning the points of each
file a unique point source ID (aka flight line number), and then
creates an overlap raster as well as a difference raster with a step
of 3 units. The overlap raster uses the default range of 5 overlaps
lines for the color ramp. The difference raster uses '-max_diff 2'
and maps range (-2 ... 0 ... 2) to colors (blue ... white ... red).

>> lasoverlap -i LDR*.las -files_are_flightlines -step 3 -min_diff 1 -max_diff 2

same as above. But here the difference raster uses '-min_diff 1' and
'-max_diff 2' to map range (-2 ... -1) to color ramp (blue ... white),
range (-1 ... +1) to white and (+1 ... +2) to (white ... red).

>> lasoverlap -i LDR*.las -files_are_flightlines -step 2 -max_diff 4 -no_over

same as above but does not output an overlap raster ('-no_over') and
operates with different '-step 2' and '-max_diff 4' settings.

>> lasoverlap -i LDR*.las -files_are_flightlines -step 5 -no_diff

same as above but does not output a difference raster ('-no_diff') but
only a coarse (-step 5) overlap raster.

>> lasoverlap -i tiles*.laz -step 2 -no_over -utm 15N

operates tile by tile (e.g. creates one difference raster per file)
and generates a Google Earth KML file for each tile using UTM 15N. It
is necessary that the LiDAR points in the LAZ file have their point
source ID populated.

>> lasoverlap -i tiles*.laz -step 2 -no_over -utm 15N -intensity -highest

same as above but computes intensity differences. For intensities the
difference raster maps range -255 ... 0 ... 255 (e.g. '-max_diff 255').

>> lasoverlap -i tiles*.laz -step 2 -no_over -utm 15N -intensity -highest

same as above but computes density differences. For densities the
difference raster maps range -100 ... 0 ... 100 (e.g. '-max_diff 100').

for more info:

C:\lastools\bin>lasoverlap -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 Raster Outputs
  -o dtm.asc
  -o dsm.bil
  -o canopy.flt
  -o dtm.dtm
  -o density.xyz
  -o intensity.img
  -o hillshade.png
  -o slope.tif
  -o false_color.jpg
  -oasc -obil -oflt -oimg -opng -odtm -otif -ojpg -oxyz -nil
  -odir C:\data\hillshade (specify output directory)
  -odix _small (specify file name appendix)
  -ocut 2 (cut the last two characters from name)
LAStools (by martin@rapidlasso.com) version 140301 (unlicensed)
usage:
lasoverlap -i tile.laz -step 1 -max_diff 0.25
lasoverlap -i tile.las -step 3 -values
lasoverlap -i *.laz -step 4 -max_diff 0.75
lasoverlap -i tiles*.las -step 2 -max_over 7
lasoverlap -i tile1.las tile2.las tile3.las tile4.las -merged -step 2
lasoverlap -i swath1.las swath2.las swath3.las -files_are_flightlines -step 2
lasoverlap -i tiles*.las -merged -counter
lasoverlap -i tiles*.las -files_are_flightlines -intensity -highest
lasoverlap -h

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