Re: [LAStools] [LAScanopy] Clip edge cells if lidar only constitutes a fraction of them

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Martin Isenburg

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Jul 10, 2021, 8:45:35 PMJul 10
to LAStools - efficient command line tools for LIDAR processing
Hello Idan,

If you want to run lascanopy (or lasgrid) with "unusual plot (or step) sizes" such as 16 you should plan ahead when you do your initial tiling and create tiles that are a multiple of 16 with buffers that are also a multiple of 16.

What comes to mind would be tiles that are 1600 meters by 1600 meters or meters 800 by 800 meters or meters 400 by 400 meters in size with a buffer of 16 or 32 meters. This way you avoid all artifacts that come from partially covered cells and get nice 100 by 100, 50 by 50 or 25 by 25 rasters as output.


Martin @rapidlasso 


On Wed, Jun 10, 2020 at 5:07 PM Idan Tene <hyd...@gmail.com> wrote:
Hey!

I've been playing around with LAStools for the past few weeks - and they're amazing.

One issue I've run into lately is when using lascanopy for tiles that don't specifically align with the gridded step size.
For example, I have a tile ranging from (473000, 7245000) to (474024.9, 7246024.99) (buffered, lasinfo results below) with a grid size of 16 and it seems that the grid generated from lascanopy starts at 472992, 7244992.
This is perfect - it's aligned as I would want it to, but the edge tiles are therefore extended and most of the data is missing from those cells (50% or above).

I've been looking for clever ways to remove these edges, so I wanted to confirm (as a new user) - is the only solution to extract the info and adjust the keep_xy (i.e. keep_xy 473008 7245008 474000 7246000) so that it matches the grid size?
Or am I missing some obvious flag somewhere along the way?

lasinfo:
reporting all LAS header entries:
  file signature
:             'LASF'
  file source ID
:             0
  global_encoding
:            1
  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
:        'lasheight (200509) unlicensed'
  file creation day
/year:     251/2016
  header size
:                227
  offset to point data
:       321
  number
var. length records: 1
  point data format
:          1
  point data record length
:   28
  number of point records
:    1292352
  number of points
by return: 848222 411779 31808 543 0
  scale factor x y z
:         0.01 0.01 0.01
  offset x y z
:               500000 7000000 0
  min x y z
:                  473000.00 7245000.00 -0.33
  max x y z
:                  474024.99 7246024.99 23.51
variable length header record
1 of 1:
  reserved            
43707
  user ID              
'LASF_Projection'
  record ID            
34735
  length after header  
40
  description          
'by LAStools of rapidlasso GmbH'
   
GeoKeyDirectoryTag version 1.1.0 number of keys 4
      key
1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: ModelTypeProjected
      key
3072 tiff_tag_location 0 count 1 value_offset 3067 - ProjectedCSTypeGeoKey: ETRS89 / TM35FIN(E,N)
      key
3076 tiff_tag_location 0 count 1 value_offset 9001 - ProjLinearUnitsGeoKey: Linear_Meter
      key
4099 tiff_tag_location 0 count 1 value_offset 9001 - VerticalUnitsGeoKey: Linear_Meter
LASzip compression (version 3.4r3 c2 50000): POINT10 2 GPSTIME11 2
LAStiling (idx 45, lvl 5, sub 0, bbox 470000 7239000 502000 7271000, buffer) (size 1000 x 1000, buffer 24.99)
reporting minimum
and maximum for all LAS point record entries ...
  X            
-2700000   -2597501
  Y            
24500000   24602499
  Z                
-33       2351
  intensity          
0        252
  return_number      
1          4
  number_of_returns  
1          4
  edge_of_flight_line
0          1
  scan_direction_flag
0          1
  classification      
1          6
  scan_angle_rank    
3         20
  user_data          
0        235
  point_source_ID  
201        211
  gps_time
150834941.191622 150835906.612575
number of first returns
:        848222
number of intermediate returns
: 32336
number of
last returns:         848477
number of single returns
:       436683
overview over number of returns of given pulse
: 436683 759737 93760 2172 0 0 0
histogram of classification of points
:
         
328954  unclassified (1)
         
507038  ground (2)
         
456230  high vegetation (5)
             
130  building (6)
 
+-> flagged as withheld:  46415
 
+--->           17996 of those are unclassified (1)
 
+--->           19502 of those are ground (2)
 
+--->            8917 of those are high vegetation (5)

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