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  las2las:

  reads and writes LIDAR data in the LAS format while modifing
  its contents. Examples are clipping of points to those
  that lie within a certain region specified by a bounding box
  (-clip), eliminating points that are the second return
  (-elim_return 2), that have a scan angle above some threshold
  (-elim_scan_angle_above 5), or below some intensity
  (-elim_intensity_below 15)
  Another typical use may be to extract only first (-first_only)
  returns or only last returns (-last_only). Extracting the first
  return is actually the same as eliminating all others (e.g.
  -elim_return 2 -elim_return 3, ...).
  Finally one can also only keep certain classifications. The
  option -keep_class 2 -keep_class 3 will eliminate all points
  except those that are of classification 2 or 3.
 
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example usage:

>> las2las -i in.las -verbose

lists the value ranges of all the points (similar to lasinfo.exe)

>> las2las -i in.las -o out.las -clip 63025000 483450000 63050000 483475000

clips points of in.las with x<63025000 or y<483450000 or x>63050000
or y>483475000 and stores surviving points to out.las. note that
clip expects the scaled integer values that the points are stored
with (not the floating point coordinates they represent).

>> las2las -i in.las -o out.las -eliminate_return 1

eliminates all points of in.las that are designated first returns
by the value in their return_number field and stores surviving
points to out.las.

>> las2las -i in.las -o out.las -eliminate_scan_angle_above 15

eliminates all points of in.las whose scan angle is above 15 or
below -15 and stores surviving points to out.las.

>> las2las -i in.las -o out.las -eliminate_intensity_below 1000 -remove_extra_header

eliminates all points of in.las whose intensity is below 1000 and
stores surviving points to out.las. in addition all variable headers
and any additional user headers are stripped from the file.

>> las2las -i in.las -o out.las -last_only

extracts all last return points from in.las and stores them to
out.las.

>> las2las -i in.las -o out.las -keep_class 2 -keep_class 3

extracts all points classfied as 2 or 3 from in.las and stores
them to out.las.

for more info:

C:\lastools\bin>las2las -h
usage:
las2las -remove_extra_header in.las out.las
las2las -i in.las -clip 63000000 483450000 63050000 483500000 -o out.las
las2las -i in.las -eliminate_return 2 -o out.las
las2las -i in.las -eliminate_scan_angle_above 15 -o out.las
las2las -i in.las -eliminate_intensity_below 1000 -olas > out.las
las2las -i in.las -first_only -clip 63000000 483450000 63050000 483500000 -o out.las
las2las -i in.las -last_only -eliminate_intensity_below 2000 -olas > out.las
las2las -i in.las -keep_class 2 -keep_class 3 -keep_class 4 -olas > out.las
las2las -h

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if you find bugs let me (isenburg@cs.unc.edu) know.