Determining Datum of Las Files

[cpul...@risebroadband.com]

Hi All,

I've run into a situation where retrieving point cloud files from public sources has resulted in incomplete las headers.  They don't state the geographic datum and they don't state projections.  Running lasinfo, we get something like this:  

lasinfo (170122) report for d:\Lidar\WI\Rock\T4R1201.LAS

reporting all LAS header entries:

  file signature:             'LASF'

  file source ID:             0

  global_encoding:            0

  project ID GUID data 1-4:   00000000-0000-0000-0000-000000000000

  version major.minor:        1.2

  system identifier:          ''

  generating software:        'TerraScan'

  file creation day/year:     0/0

  header size:                227

  offset to point data:       229

  number var. length records: 0

  point data format:          1

  point data record length:   28

  number of point records:    1242509

  number of points by return: 1074600 157195 10527 187 0

  scale factor x y z:         0.01 0.01 0.01

  offset x y z:               0 0 0

  min x y z:                  490423.07 323791.27 778.83

  max x y z:                  495750.71 329171.43 1109.86

the header is followed by 2 user-defined bytes

reporting minimum and maximum for all LAS point record entries ...

  X            49042307   49575071

  Y            32379127   32917143

  Z               77883     110986

  intensity           0        255

  return_number       1          4

  number_of_returns   1          4

  edge_of_flight_line 0          1

  scan_direction_flag 0          1

  classification      1         10

  scan_angle_rank   -19         16

  user_data           0          0

  point_source_ID    13         15

  gps_time 136012.066933 583035.220972

number of first returns:        1074600

number of intermediate returns: 49804

number of last returns:         674189

number of single returns:       556084

overview over number of returns of given pulse: 556084 576014 108045 2366 0 0 0

histogram of classification of points:

           53251  unclassified (1)

          321308  low vegetation (3)

          159927  medium vegetation (4)

          701424  high vegetation (5)

              98  noise (7)

            4987  water (9)

            1514  rail (10)

Is there a way to find the geographic data or the spatial reference from files like this?  I have a lot of data that looks the same.

Thanks,

Collin

[Evon Silvia]

Looks like state plane coordinates to me based on the min/max XYZ values, but no way for me to know for sure without more information.

If the CRS information is missing or incomplete in the LAS/LAZ file itself, usually LAS files from public sources will have a XML or readme.txt file packaged with them that has that information in some form. You might also have a shapefile packaged with the LAS/LAZ with a PRJ that has the WKT definition.

If all else fails, call/email the data provider. They should know what it's in.

Evon

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[Martin Isenburg]

Hello,

if it is indeed state plane and in meters then you could run:

las2dem -i d:\Lidar\WI\Rock\T4R1201.LAS -keep_first -hillshade -nad83 -sp83 WI_N -opng

las2dem -i d:\Lidar\WI\Rock\T4R1201.LAS -keep_first -hillshade -nad83 -sp83 WI_C -opng

las2dem -i d:\Lidar\WI\Rock\T4R1201.LAS -keep_first -hillshade -nad83 -sp83 WI_S -opng

and check if the resulting KML file "lands" at the right place. If the horizontal coordinate are in US feet (sigh ...) then look up the EPSG codes for Wisconsin which seem to be:

EPSG:2287: NAD83 / Wisconsin North (ftUS)

EPSG:2288: NAD83 / Wisconsin Central (ftUS)

EPSG:2289: NAD83 / Wisconsin South (ftUS)

according to 

http://www.spatialreference.org/ref/?search=Wisconsin

and try

las2dem -i d:\Lidar\WI\Rock\T4R1201.LAS -keep_first -hillshade -epsg 2287 -opng

las2dem -i d:\Lidar\WI\Rock\T4R1201.LAS -keep_first -hillshade -epsg 2288 -opng

las2dem -i d:\Lidar\WI\Rock\T4R1201.LAS -keep_first -hillshade -epsg 2289 -opng

Regards,

Martin @rapidlasso

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[cpul...@risebroadband.com]

Finding the metadata proved harder than expected, but it turns out is is in NAD83 county data.

Thank you for the responses, all.