clarification "number of point records" versus "extended number of point records"

9 views
Skip to first unread message

Martin Isenburg

unread,
Aug 27, 2017, 2:13:37 PM8/27/17
to The LAS room - a friendly place to discuss specifications of the LAS format, LAStools - efficient command line tools for LIDAR processing
Hello,

I received the question on why the number of point records that lasinfo reported is 0 when the sum of the totals listed in the classified histogram reports is 78585827.
histogram of classification of points. See lasinfo report below. This "bug" was repoted to only have occurred with LAS 1.4 files. 

The reason is simple. For point types 6 and higher the "legacy" 32 bit counter fields in the header of a LAS 1.4 file *MUST* be set to zero and the "extended" 64 bit counters of the header are supposed to hold the correct counts instead. This was done as a simple way to prevent old software from trying to read (unknown) new point types 6 through 10 that are possible in LAS 1.4 but at the same time allow old software to read point types 0 to 5 if stored in a LAS 1.4 file. This is indeed the case (see fields marked in red below).

Regards.

Martin @rapidlasso

---------------------

reporting all LAS header entries:
  file signature:             'LASF'
  file source ID:             0
  global_encoding:            17
  project ID GUID data 1-4:   00000000-0000-0000-0000-000000000000
  version major.minor:        1.4
  system identifier:          'HARRIS INTELLIEARTH GEIGER MODE'
  generating software:        'LASzip DLL 2.2 r0 (130917)'
  file creation day/year:     185/2017
  header size:                375
  offset to point data:       1772
  number var. length records: 1
  point data format:          6
  point data record length:   30
  number of point records:    0
  number of points by return: 0 0 0 0 0
  scale factor x y z:         0.00001 0.00001 0.00001
  offset x y z:               1620499.9950000001 6628499.9950000001 460.625
  min x y z:                  1620000.00000 6628000.00000 445.28000
  max x y z:                  1620999.99000 6628999.99000 475.97000
  start of waveform data packet record: 0
  start of first extended variable length record: 0
  number of extended_variable length records: 0
  extended number of point records: 78585827
  extended number of points by return: 78585827 0 0 0 0 0 0 0 0 0 0 0 0 0 0
variable length header record 1 of 1:
  reserved             0
  user ID              'LASF_Projection'
  record ID            2112
  length after header  1343
  description          'Projection'
    WKT OGC COORDINATE SYSTEM:
    COMPD_CS["NAD83(2011) / Texas Centric Lambert Conformal + NAVD88 height - Geoid12B",

    PROJCS["NAD83(2011) / Texas Centric Lambert Conformal",

        GEOGCS["NAD83(2011)",

            DATUM["NAD83_National_Spatial_Reference_System_2011",

                SPHEROID["GRS 1980",6378137,298.257222101,

                    AUTHORITY["EPSG","7019"]],

                AUTHORITY["EPSG","1116"]],

            PRIMEM["Greenwich",0,

                AUTHORITY["EPSG","8901"]],

            UNIT["degree",0.0174532925199433,

                AUTHORITY["EPSG","9122"]],

            AUTHORITY["EPSG","6318"]],

        PROJECTION["Lambert_Conformal_Conic_2SP"],

        PARAMETER["standard_parallel_1",27.5],

        PARAMETER["standard_parallel_2",35],

        PARAMETER["latitude_of_origin",18],

        PARAMETER["central_meridian",-100],

        PARAMETER["false_easting",1500000],

        PARAMETER["false_northing",5000000],

        UNIT["metre",1,

            AUTHORITY["EPSG","9001"]],

        AXIS["X",EAST],

        AXIS["Y",NORTH],

        AUTHORITY["EPSG","6580"]],

    VERT_CS["NAVD88 height",

        VERT_DATUM["North American Vertical Datum 1988",2005,

            AUTHORITY["EPSG","5103"]],

        UNIT["metre",1,

            AUTHORITY["EPSG","9001"]],

        AXIS["Up",UP],

        AUTHORITY["EPSG","5703"]]]
reporting minimum and maximum for all LAS point record entries ...
  X           -49999500   49999499
  Y           -49999500   49999500
  Z            -1534499    1534500
  intensity           0      65535
  return_number       1          1
  number_of_returns   1          1
  edge_of_flight_line 0          0
  scan_direction_flag 0          0
  classification      0          7
  scan_angle_rank    15         15
  user_data           0          0
  point_source_ID     0          0
  gps_time 174893536.000000 174895488.000000
  extended_return_number          1      1
  extended_number_of_returns      1      1
  extended_classification         1     81
  extended_scan_angle          2500   2500
  extended_scanner_channel        0      0
number of first returns:        78585827
number of intermediate returns: 0
number of last returns:         78585827
number of single returns:       78585827
overview over extended number of returns of given pulse: 78585827 0 0 0 0 0 0 0 0 0 0 0 0 0 0
histogram of classification of points:
        51205062  unclassified (1)
        27379130  ground (2)
               1  noise (7)
histogram of extended classification of points:
             112  extended classification (70)
             733  extended classification (72)
             757  extended classification (80)
              32  extended classification (81)
Reply all
Reply to author
Forward
0 new messages