Classify Scan angle Above and Below... to Noise

[Steeve Brissette]

Hi. I have been searching all over the forum before post my question, and I have read READ_ME files. Without success. I hope I didn't missed the obvious : )

I tryied to classify scan angle over and below [noise>25 and -25> noise] scan angle to noise like so.

las2las   -i foo.laz    -keep_scan_angle_below -25    -keep_scan_angle_above 25    -filtered_transform    -set_classification 7   -odir C:\output   -olaz

I have learned about -filtered_transform in those two post posts only, but it didn't work quite good for me. But I am sure this can help me...

Here...

https://groups.google.com/forum/#!searchin/lastools/filtered$20transforms%7Csort:date/lastools/jUMmRqL206I/M22vKtVDBgAJ

And here...

https://groups.google.com/forum/#!searchin/lastools/filtered$20transforms%7Csort:date/lastools/P95PiczMtEA/GfB4yuLDEAAJ

I just need to know if this is the actual approach, using filtered_transform option? Im a little confuse by the results actually... any help/suggestions would by appreciated.

Thanks

Steeve

[Martin Isenburg]

Hello Steeve,

you'll have to design your filter differently. There are some issues with your filter

(a) the filters in your command line don't exist, only the corresponding '-drop_....' do

(b) all points would be filtered as no point can survive both filters since no scan angle can be both below -25 and above 25 at the same time

(c) because all points are filtered there are no survivors and the filtered_transform does not transform any points

however, there is a '-drop_abs_scan_angle_below 25' so for you this should work:

las2las -i foo.laz ^

            -drop_abs_scan_angle_below 25 ^

            -filtered_transform ^

            -set_classification 7 ^

            -odir C:\output -olaz

here an example with 'zurich.laz' from the LAStools\data folder:

E:\LAStools\bin> lasinfo -i ..\data\zurich.laz -histo scan_angle 2

lasinfo (180303) report for ..\data\zurich.laz

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:        'lassort (150812) commercial'

  file creation day/year:     16/2015

  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:    656837

  number of points by return: 467357 107076 47254 21904 8935

  scale factor x y z:         0.01 0.01 0.01

  offset x y z:               0 0 0

  min x y z:                  676750.00 246000.00 547.29

  max x y z:                  676849.99 246099.99 573.87

the header is followed by 2 user-defined bytes

LASzip compression (version 2.4r0 c2 50000): POINT10 2 GPSTIME11 2

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

  X            67675000   67684999

  Y            24600000   24609999

  Z               50623      57390

  intensity           1       7669

  return_number       1          7

  number_of_returns   1          7

  edge_of_flight_line 0          0

  scan_direction_flag 0          0

  classification      2         17

  scan_angle_rank   -20         29

  user_data           0          0

  point_source_ID  2404      10102

  gps_time 78474513.065274 80531980.003439

WARNING: 228 points outside of header bounding box

number of first returns:        467357

number of intermediate returns: 82506

number of last returns:         466716

number of single returns:       359742

WARNING: there are 3160 points with return number 6

WARNING: there are 1151 points with return number 7

overview over number of returns of given pulse: 359742 119359 76362 52315 28914 13431 6714

histogram of classification of points:

          171354  ground (2)

           20228  low vegetation (3)

           37072  medium vegetation (4)

           98061  high vegetation (5)

          156178  building (6)

             579  noise (7)

          172798  overlap (12)

             567  bridge deck (17)

scan angle histogram with bin size 2

  bin [-20,-18) has 22512

  bin [-18,-16) has 23127

  bin [-16,-14) has 31445

  bin [-14,-12) has 21446

  bin [-12,-10) has 24483

  bin [-10,-8) has 5612

  bin [-2,0) has 13278

  bin [0,2) has 49884

  bin [2,4) has 38238

  bin [4,6) has 39375

  bin [6,8) has 32909

  bin [8,10) has 100259

  bin [10,12) has 102589

  bin [12,14) has 34353

  bin [20,22) has 8562

  bin [22,24) has 26781

  bin [24,26) has 34325

  bin [26,28) has 27855

  bin [28,30) has 19804

  average scan angle 5.812484680369711 for 656837 element(s)

real max z larger than header max z by 0.030000

real min z smaller than header min z by 41.060000

E:\LAStools\bin> lasview -i ..\data\zurich.laz ^

                                        -drop_abs_scan_angle_below 5 ^

                                        -filtered_transform ^

                                        -set_classification 7

E:\LAStools\bin> las2las -i ..\data\zurich.laz ^

                                        -drop_abs_scan_angle_below 5 ^

                                        -filtered_transform ^

                                        -set_classification 7 ^

                                        -odix _filtered -olaz

E:\LAStools\bin> lasinfo -i ..\data\zurich_filtered.laz ^

                                      -drop_class 7 ^

                                      -histo scan_angle 1

Regards,

Martin @rapidlasso

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