Lasinfo Warning(s)

[Veldman, Edgar]

Hi Martin,

Why am I getting all these warnings? I know you care, but three subsequent warnings?

WARNING: there is coordinate resolution fluff in XYZ
WARNING: there is serious coordinate resolution fluff in XY
WARNING: there is very serious coordinate resolution fluff in XY

I think I get it. There is a bit of resolution fluff in my lasfile :)

Edgar

[Martin Isenburg]

Hello,

These WARNINGS were recently added as I keep on seeing centimeter resolution LiDAR being stored with millimeter resolution to the LAS file (e.g. xyz scale facors of 0.001) which means that all scaled integers are multiple of 10 and that negatively affects compression and gives users the impression they may have more accuracy in the data than they actually do.

I assume you are using lasinfo with (on-the-fly-converted ASC or BIL or DTM?) raster input where the X and the Y coordinate are on a meter raster while the Z coordinate is on a centimeter raster but uses a scale factor of 0.001? Well ... in this case the output is a bit verbose, I agree. But if you used "real" LiDAR as input then you need these many WARNINGS because then things were really bad.

Cheers,

Martin

PS: These warnings have also been added to lasvalidate. Prior to this lasprecision was the tool to check for "resolution fluff".

[anpl...@gmail.com]

Hello,

I'm getting the first two warnings:

WARNING: there is coordinate resolution fluff (x10) in XY
WARNING: there is serious coordinate resolution fluff (x100) in XY

when I run lasinfo in the laz files of a DTM. The resolution is cm and the scale factor x y z is 0.01 0.01 0.01, so I think this is not the problem, but then I don't know what it is.

Would be great to get some help.

Andrea

[Martin Isenburg]

Hello,

please send the *complete* lasinfo report for the LAZ file in question. Otherwise it's hard to say what the issue is.

http://rapidlasso.com/lasinfo

Regards,

Martin @rapidlasso

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[Andrea Plazas]

Hello Martin,

thanks for the quick answer, here it is:

lasinfo (181001) report for 'temp_ground_strips\25955720.laz'
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:          'LAStools (c) by rapidlasso GmbH'
  generating software:        'las2las (version 181001)'
  file creation day/year:     94/2018
  header size:                227
  offset to point data:       227
  number var. length records: 0
  point data format:          0
  point data record length:   20
  number of point records:    1000000
  number of points by return: 1000000 0 0 0 0
  scale factor x y z:         0.01 0.01 0.01
  offset x y z:               500000 5700000 0
  min x y z:                  595000.00 5720000.00 232.55
  max x y z:                  595999.00 5720999.00 313.63
LASzip compression (version 3.2r5 c2 50000): POINT10 2
reporting minimum and maximum for all LAS point record entries ...
  X             9500000    9599900
  Y             2000000    2099900
  Z               23255      31363
  intensity           0          0
  return_number       1          1
  number_of_returns   1          1
  edge_of_flight_line 0          0
  scan_direction_flag 0          0
  classification     31         31
  scan_angle_rank     0          0
  user_data           0          0
  point_source_ID     0          0

WARNING: there is coordinate resolution fluff (x10) in XY
WARNING: there is serious coordinate resolution fluff (x100) in XY

number of first returns:        1000000
number of intermediate returns: 0
number of last returns:         1000000
number of single returns:       1000000
overview over number of returns of given pulse: 1000000 0 0 0 0 0 0
histogram of classification of points:
         1000000  Reserved for ASPRS Definition (31)

Regards,

Andrea

[Martin Isenburg]

Hello,

http://rapidlasso.com/las2las

http://lastools.org/download/las2las_README.txt

it seems that this file was generated with las2las from an (XYZ?) raster whose x/y coordinates lie exactly on the full meters. 

595000.00 5720000.00 232.55

595001.00 5720000.00 234.65

595002.00 5720000.00 233.45

595003.00 5720000.00 234.21

[...]

595999.00 5720000.00 262.61

595000.00 5720001.00 232.77

595001.00 5720001.00 233.32

595002.00 5720001.00 234.01

[...]  

By default LAStools uses centimeters (aka uses scale factors of 0.01) to store all coordinates unless specified otherwise. As the ten centimeters and the centimeter digit of all x/y coordinates is zero this is reported as (harmless) "fluff". Gridded coordinates are predicted perfectly so fluff is less serious than for real LiDAR when it comes to compression.

By adding '-set_scale 1.0 1.0 0.01' to your las2las call you can remove the fluff. DANGER: When your grid is sampled in the cell centers you need to use either '-set_scale 0.5 0.5 0.01' or '-set_scale 0.1 0.1 0.01'. If in doubt and not sure how to properly convert grids to LAS/LAZ points then live with "fluff" or you risk to quantize / shift your grid accidentally.

595000.50 5720000.50 232.55

595001.50 5720000.50 234.65

595002.50 5720000.50 233.45

595003.50 5720000.50 234.21

[...]

595999.50 5720000.50 262.61

595000.50 5720001.50 232.77

595001.50 5720001.50 233.32

595002.50 5720001.50 234.01

[...]  

Regards.

Martin