lasvoxel: setting a starting coordinate?

[Jonathan Greenberg]

I am hoping to use lasvoxel for change detection between two different LAS files that may have different origination points -- is there a way to start both lasvoxels so the x,y,z voxel coordinates are "aligned" (assuming points exist within the voxel, they both get the exact same x,y,z that can be joined later on?)

[Martin Isenburg]

Hello,

Jonathan had clarified this question off list:

"Sorry if my previous question wasn't clear.  I'll try to make an example, but given two .laz files representing lidar data collected at time 1 and time 2, e.g. T1.laz and T2.laz, what I'm trying to do is determine the change in e.g. voxelized point counts between those two time periods.  The way I was thinking about it was I voxelize T1, separately voxelize T2, export both to a CSV file, and then merge the two based on their x,y,z positions.  I'm trying to end up with a database that looked something like:

Voxel X, Voxel Y, Voxel Z, # of points in T1, # of points in T2

The issue I'm thinking I'm going to run into is that the origin of the voxels in T1 and T2 will likely be different, e.g. say T1 the origin corner coordinate is 0, 0, 0 and T2 its 0.5, 0.5, 0.5.  Say I use a 1m voxel.  The resultant x,y,z of the voxels from T1 and T2 will be off by 0.5 meters (so I can't do a join without fixing this) and will represent slightly different volumes of space.  What I'd like to use is the same voxel origin for BOTH time periods (e.g. the voxels always start at 0,0,0 even if the actual .laz origin has some decimal)."

Turns out this question was unnecessary because the voxel locations are globally unique as the voxel grid is globally aligned and uniquely defined by the step size. There should not be a shift. 

The other question was: How do I get the number of points per voxel?

This is stored in the intensity. Below an example.

C:\LAStools\bin>lasvoxel -i ..\data\fusa.laz -step 2 -compute_mean_xyz -o fusa_v.laz

done with 'fusa_v.laz'. took 0.186 sec.

C:\LAStools\bin>lasview -i fusa_v.laz

C:\LAStools\bin>las2txt -i fusa_v.laz -parse ixyz -stdout | more

17 277750.97 6122251.04 42.30

17 277752.98 6122251.01 42.29

12 277754.87 6122250.93 43.06

3 277756.79 6122251.60 42.30

1 277758.40 6122251.12 42.60

1 277760.04 6122251.03 43.25

1 277767.15 6122251.80 43.59

18 277768.78 6122251.06 43.59

22 277770.98 6122250.91 43.63

13 277773.15 6122251.02 43.67

15 277774.76 6122250.88 43.70

22 277776.93 6122250.96 43.74

17 277779.09 6122251.03 43.82

16 277781.14 6122250.96 43.84

16 277783.02 6122251.03 43.91

15 277784.95 6122250.98 43.96

2 277786.64 6122250.25 43.99

15 277750.89 6122253.00 42.39

16 277752.98 6122253.04 42.38

6 277754.54 6122253.08 42.50

4 277757.20 6122252.50 42.34

2 277758.38 6122252.32 42.33

3 277762.56 6122253.11 43.44

7 277767.28 6122252.86 43.59

[...]

C:\LAStools\bin>lasinfo -i fusa_v.laz

lasinfo (180907) report for 'fusa_v.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:        'lasvoxel (180907) commercial'

  file creation day/year:     0/0

  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:    26837

  number of points by return: 26837 0 0 0 0

  scale factor x y z:         0.01 0.01 0.01

  offset x y z:               200000 6100000 0

  min x y z:                  277750.05 6122250.01 42.26

  max x y z:                  277999.97 6122499.87 64.32

LASzip compression (version 3.2r4 c2 50000): POINT10 2

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

  X             7775005    7799997

  Y             2225001    2249987

  Z                4226       6432

  intensity           1         32

  return_number       1          1

  number_of_returns   1          1

  edge_of_flight_line 0          0

  scan_direction_flag 0          0

  classification      0          0

  scan_angle_rank     0          0

  user_data           0          0

  point_source_ID     0          0

number of first returns:        26837

number of intermediate returns: 0

number of last returns:         26837

number of single returns:       26837

overview over number of returns of given pulse: 26837 0 0 0 0 0 0

histogram of classification of points:

           26837  never classified (0)

On Mon, Aug 20, 2018 at 7:24 PM Jonathan Greenberg <jgr...@gmail.com> wrote:

I am hoping to use lasvoxel for change detection between two different LAS files that may have different origination points -- is there a way to start both lasvoxels so the x,y,z voxel coordinates are "aligned" (assuming points exist within the voxel, they both get the exact same x,y,z that can be joined later on?)

--
Download LAStools at
http://lastools.org
http://rapidlasso.com
Be social with LAStools at
http://facebook.com/LAStools
http://twitter.com/LAStools
http://linkedin.com/groups/LAStools-4408378
Manage your settings at
http://groups.google.com/group/lastools/subscribe