Validade .LAS files

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Dennis Bernardi

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Nov 26, 2018, 10:10:09 AM11/26/18
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Martin, good morning

 

There is any form from validate .las files, my questions is because, is possible interpolate points and add this points in .las files, correct.

 

·         How is possible to validate, if .las files are only originals point in .las, aquiring at the flight plan?

·         If this occour, is possible identify interpolated points in .las files?

 

Regards

 

Dennis Bernardi

Coordenador Corporativo

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dennis....@fibria.com.br

Cel 55 12  99704 5301

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Martin Isenburg

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Nov 26, 2018, 11:18:49 PM11/26/18
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Hello,

interesting. So you are looking for LAS files that have been "tampered" with or that are "fudged" to get the intended coverage that was not actually achieved by the survey flight? I'm sure we would find that out via looking for discontinuities in the GPS time stamps and/or the return numbering using a combination of lassort, lasreturn, lasinfo, lasplit, and so on. Or maybe a simple lasinfo report (*) with the added option '-histo gps_time 5' may be sufficient to evaluate that.  

Maybe you could share a sample LAZ file (only a link) or provide a lasinfo report with the aforementioned option?
 
Regards from Sri Lanka,

Martin @rapidlasso


Martin Isenburg

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Nov 27, 2018, 8:43:14 AM11/27/18
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Hello,

we received a copy of a "sample" LAZ file that is expected to be fudged. The lasinfo report (see the end of this file) shows nothing suspicious. The GPS time stamp hisotgram suggests the file has three flight lines that are not properly marked with point source ID numbers but that is often the case. Next thing to check is for duplicates and for a correct return numbering. Again nothing suspicious for the xyz duplicates. Only 2 and that can happen with multiple flightlines.

C:\LAStools\bin>lasduplicate -i Tile_H007_345750_7669750.laz -unique_xyz -nil
found 2 duplicates in 'Tile_H007_345750_7669750.laz'. took 1.594 sec.

Then we sort to bring all returns from the same shot next to each other.

C:\LAStools\bin>lassort -i Tile_H007_345750_7669750.laz -gps_time -return_number -odix _sorted -olaz
done with 'Tile_H007_345750_7669750_sorted.laz'. took 1.223 sec.

Then we check whether there are missing or duplicate returns. BINGO! We found something unusual. The number of missing returns is normal (those tend to be missing along the tile edges as laser shots are not all perfectly vertical) but there is an insane number of duplicate returns.

C:\LAStools\bin>lasreturn -i Tile_H007_345750_7669750_sorted.laz -check_return_numbering
checked returns of 341230 multi and 824 single return pulses. took 0.511 secs
missing: 601 duplicate: 431281 too large: 0 zero: 0
missing
=======
25 returns with n = 2 and r = 1 are missing
520 returns with n = 2 and r = 2 are missing
6 returns with n = 3 and r = 1 are missing
24 returns with n = 3 and r = 2 are missing
26 returns with n = 3 and r = 3 are missing
duplicate
========
253961 returns with n = 1 and r = 1 are duplicate
83775 returns with n = 2 and r = 1 are duplicate
83278 returns with n = 2 and r = 2 are duplicate
3404 returns with n = 3 and r = 1 are duplicate
3389 returns with n = 3 and r = 2 are duplicate
3386 returns with n = 3 and r = 3 are duplicate
22 returns with n = 4 and r = 1 are duplicate
22 returns with n = 4 and r = 2 are duplicate
22 returns with n = 4 and r = 3 are duplicate
22 returns with n = 4 and r = 4 are duplicate

We split the file into its three different flightlines:

C:\LAStools\bin>lassplit -i Tile_H007_345750_7669750_sorted.laz -recover_flightlines -o Tile_H007_strip.laz

We check the shortest strip that contains only 107 returns and find it has a whopping 51 duplicate returns.

C:\LAStools\bin>lasreturn -check_return_numbering -i Tile_H007_strip_0000002.laz
checked returns of 50 multi and 5 single return pulses. took 0 secs
missing: 0 duplicate: 51 too large: 0 zero: 0
duplicate
========
49 returns with n = 1 and r = 1 are duplicate
1 returns with n = 2 and r = 1 are duplicate
1 returns with n = 2 and r = 2 are duplicate

We output the points as ASCII text to see how these duplicate points are different from another. The characters "_!@" in the parse string list the difference of the raw integer in the LAS format to the previous point. BINGO! We found the issue. Below I marked the first few pairs of duplicate returns in the same color. You will find that they are always 17 cm apart in x and also 17 cm apart in y and also 1 cm apart in z. Hence at least around half the points in the file are simply slightly translated (17 -17 -1) or (-17 17 1) duplicates of the other points. Also their intensities are identical which means it is really the same return in two slightly shifted locations. I also find other oddly regular differences between points that are 28 -28 -1 or similar that may explain the "streak-ish" appearance of the point cloud in lasview.

C:\LAStools\bin>lasview -i Tile_H007_strip_0000002.laz -color_by_return -point_size 10

I am not sure whether this was "fudged" on purpose or whether the export software is simply buggy. But you have less than half the density that there really is and certainly the "translation" means that each one of the two copies is sqrt(17^2+17^2+1^2) = 24.0 cm off the true location.

C:\LAStools\bin>las2txt -i Tile_H007_strip_0000002.laz -parse "trnixyz_!@" -stdout | more
518288.393605 1 1 20479 345999.97 7669764.22 351.60 34599997 766976422 35160
518288.432207 1 1 37060 345999.20 7669762.60 349.92 -77 -162 -168
518288.432207 1 1 37060 345999.37 7669762.43 349.91 17 -17 -1
518288.432212 1 1 34176 345999.67 7669762.14 349.94 30 -29 3
518288.432212 1 1 34176 345999.84 7669761.97 349.93 17 -17 -1
518288.457935 1 1 26246 345999.83 7669760.42 352.70 -1 -155 277
518288.483673 1 1 37617 345998.68 7669759.85 349.87 -115 -57 -283
518288.483673 1 1 37617 345998.85 7669759.68 349.86 17 -17 -1
518288.496538 1 1 39419 345998.43 7669759.39 349.84 -42 -29 -2
518288.496538 1 1 39419 345998.60 7669759.22 349.83 17 -17 -1
518288.496543 1 1 35126 345998.87 7669758.96 349.79 27 -26 -4
518288.496543 1 1 35126 345999.04 7669758.79 349.78 17 -17 -1
518288.509402 1 1 21626 345998.26 7669758.88 349.88 -78 9 10
518288.509402 1 1 21626 345998.09 7669759.05 349.89 -17 17 1
518288.509412 1 1 39419 345998.97 7669758.17 349.79 88 -88 -10
518288.509412 1 1 39419 345999.14 7669758.00 349.78 17 -17 -1
518288.535115 1 1 36797 345996.06 7669759.13 349.92 -308 113 14
518288.535115 1 1 36797 345995.89 7669759.30 349.93 -17 17 1
518288.535120 1 1 35847 345996.54 7669758.67 349.92 65 -63 -1
518288.535120 1 1 35847 345996.37 7669758.84 349.93 -17 17 1
518288.535160 1 1 38108 345999.99 7669755.25 349.73 362 -359 -20
518288.547979 1 1 40271 345995.77 7669758.89 349.90 -422 364 17
518288.547979 1 1 40271 345995.60 7669759.06 349.91 -17 17 1
518288.548004 1 1 33652 345999.85 7669754.84 354.23 425 -422 432
518288.548014 1 1 34799 345998.95 7669755.73 349.77 -90 89 -446
518288.548014 1 1 34799 345998.78 7669755.90 349.78 -17 17 1
518288.548024 1 1 40074 345999.69 7669755.00 349.73 91 -90 -5
518288.548024 1 1 40074 345999.86 7669754.83 349.72 17 -17 -1
518288.560848 1 1 26738 345995.55 7669758.09 349.92 -431 326 20
518288.560848 1 1 26738 345995.72 7669757.92 349.91 17 -17 -1
518288.560853 1 1 41155 345996.17 7669757.47 349.90 45 -45 -1
518288.560853 1 1 41155 345996.00 7669757.64 349.91 -17 17 1
518288.560878 1 1 36634 345998.46 7669755.19 349.82 246 -245 -9
518288.560878 1 1 36634 345998.29 7669755.36 349.83 -17 17 1
518288.560883 1 1 41352 345998.70 7669754.96 349.74 41 -40 -9
518288.560883 1 1 41352 345998.87 7669754.79 349.73 17 -17 -1
518288.573707 1 1 32341 345994.93 7669757.74 349.94 -394 295 21
518288.573707 1 1 32341 345994.76 7669757.91 349.95 -17 17 1
518288.573712 1 1 38796 345995.39 7669757.28 349.93 63 -63 -2
518288.573712 1 1 38796 345995.22 7669757.45 349.94 -17 17 1
518288.573717 1 1 39288 345995.67 7669757.01 349.88 45 -44 -6
518288.573717 1 1 39288 345995.84 7669756.84 349.87 17 -17 -1
518288.573722 1 1 40795 345996.12 7669756.56 349.86 28 -28 -1
518288.573722 1 1 40795 345996.29 7669756.39 349.85 17 -17 -1
518288.573737 1 1 38665 345997.48 7669755.21 349.78 119 -118 -7
518288.573737 1 1 38665 345997.65 7669755.04 349.77 17 -17 -1
518288.573752 1 1 38370 345998.84 7669753.86 349.71 119 -118 -6
518288.573752 1 1 38370 345999.01 7669753.69 349.70 17 -17 -1
518288.586576 1 1 37846 345995.01 7669756.96 349.95 -400 327 25
518288.586576 1 1 37846 345994.84 7669757.13 349.96 -17 17 1
518288.586631 1 1 39320 345999.96 7669752.04 349.65 512 -509 -31
518288.586631 1 1 39320 345999.79 7669752.21 349.66 -17 17 1
518288.599440 1 1 35323 345994.54 7669756.57 349.98 -525 436 32
518288.599440 1 1 35323 345994.37 7669756.74 349.99 -17 17 1
518288.599490 1 1 36208 345998.88 7669752.27 349.72 451 -447 -27
518288.599490 1 1 36208 345999.05 7669752.10 349.71 17 -17 -1
518288.599495 1 1 40697 345999.48 7669751.67 349.63 43 -43 -8
518288.599495 1 1 40697 345999.31 7669751.84 349.64 -17 17 1
518288.599500 1 1 38436 345999.91 7669751.24 349.57 60 -60 -7
518288.599500 1 1 38436 345999.74 7669751.41 349.58 -17 17 1
518288.612299 1 2 25427 345994.35 7669755.76 351.49 -539 435 191
518288.612299 1 2 25427 345994.18 7669755.93 351.50 -17 17 1
518288.612299 2 2 27688 345993.68 7669756.45 349.98 -50 52 -152
518288.612299 2 2 27688 345993.51 7669756.62 349.99 -17 17 1
518288.612334 1 1 39550 345996.84 7669753.29 349.79 333 -333 -20
518288.612334 1 1 39550 345996.67 7669753.46 349.80 -17 17 1
518288.612349 1 1 31030 345998.19 7669751.96 349.71 152 -150 -9
518288.612349 1 1 31030 345998.02 7669752.13 349.72 -17 17 1
518288.612354 1 1 39353 345998.63 7669751.52 349.68 61 -61 -4
518288.612354 1 1 39353 345998.46 7669751.69 349.69 -17 17 1
518288.625173 1 1 28245 345993.99 7669755.35 349.91 -447 366 22
518288.625173 1 1 28245 345994.16 7669755.18 349.90 17 -17 -1
518288.625208 1 1 29916 345997.16 7669752.19 349.74 300 -299 -16
518288.625208 1 1 29916 345997.33 7669752.02 349.73 17 -17 -1
518288.625218 1 1 39255 345998.04 7669751.32 349.66 71 -70 -7
518288.625218 1 1 39255 345998.21 7669751.15 349.65 17 -17 -1
518288.625223 1 1 37944 345998.54 7669750.83 349.72 33 -32 7
518288.625223 1 1 37944 345998.71 7669750.66 349.71 17 -17 -1
518288.638027 1 1 25951 345992.67 7669755.66 349.92 -604 500 21
518288.638027 1 1 25951 345992.50 7669755.83 349.93 -17 17 1
518288.638062 1 1 38010 345995.69 7669752.66 349.82 319 -317 -11
518288.638062 1 1 38010 345995.86 7669752.49 349.81 17 -17 -1
518288.638067 1 1 37944 345996.15 7669752.22 349.80 29 -27 -1
518288.638067 1 1 37944 345996.32 7669752.05 349.79 17 -17 -1
518288.638088 1 1 38862 345997.92 7669750.45 349.63 160 -160 -16
518288.638088 1 1 38862 345998.09 7669750.28 349.62 17 -17 -1
518288.650922 1 1 31325 345994.88 7669752.70 349.78 -321 242 16
518288.650922 1 1 31325 345995.05 7669752.53 349.77 17 -17 -1
518288.650927 1 1 32439 345995.38 7669752.21 349.88 33 -32 11
518288.650927 1 1 32439 345995.55 7669752.04 349.87 17 -17 -1
518288.650942 1 1 40500 345996.70 7669750.90 349.72 115 -114 -15
518288.650942 1 1 40500 345996.87 7669750.73 349.71 17 -17 -1
518288.663786 1 1 39386 345994.37 7669752.37 349.77 -250 164 6
518288.663786 1 1 39386 345994.54 7669752.20 349.76 17 -17 -1
518288.663806 1 1 33684 345996.19 7669750.55 349.71 165 -165 -5
518288.663806 1 1 33684 345996.36 7669750.38 349.70 17 -17 -1
518288.663811 1 1 40762 345996.63 7669750.11 349.68 27 -27 -2
518288.676650 1 1 34668 345993.93 7669751.69 349.81 -270 158 13
518288.676650 1 1 34668 345993.76 7669751.86 349.82 -17 17 1
518288.689514 1 1 26738 345993.37 7669751.42 349.83 -39 -44 1
518288.689514 1 1 26738 345993.54 7669751.25 349.82 17 -17 -1
518288.702363 1 1 26410 345993.93 7669750.20 355.16 39 -105 534
518288.702363 1 1 26410 345994.10 7669750.03 355.15 17 -17 -1
518288.766673 1 1 28606 345988.20 7669750.94 350.05 -590 91 -510
518288.766673 1 1 28606 345988.03 7669751.11 350.06 -17 17 1
518288.766678 1 1 24641 345988.46 7669750.69 349.98 43 -42 -8
518288.766678 1 1 24641 345988.63 7669750.52 349.97 17 -17 -1

======================================================================

nothing unusual in the lasinfo report

C:\LAStools\bin>lasinfo -i Tile_H007_345750_7669750.laz -histo gps_time 1
lasinfo (181119) report for 'Tile_H007_345750_7669750.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:        'lastile (181001) commercial'
  file creation day/year:     329/2018
  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:    863664
  number of points by return: 683185 173612 6823 44 0
  scale factor x y z:         0.01 0.01 0.01
  offset x y z:               0 0 0
  min x y z:                  345750.00 7669750.00 349.32
  max x y z:                  345999.99 7669999.99 369.39
the header is followed by 2 user-defined bytes
LASzip compression (version 3.2r5 c2 50000): POINT10 2 GPSTIME11 2
LAStiling (idx 9465, lvl 8, sub 0, bbox 334500 7.65025e+006 398500 7.71425e+006)
reporting minimum and maximum for all LAS point record entries ...
  X            34575000   34599999
  Y           766975000  766999999
  Z               34932      36939
  intensity        7307      46038
  return_number       1          4
  number_of_returns   1          4
  edge_of_flight_line 0          1
  scan_direction_flag 0          0
  classification      2          5
  scan_angle_rank   -16         33
  user_data           0          0
  point_source_ID     0          0
  gps_time 517976.206160 519690.081370
number of first returns:        683185
number of intermediate returns: 6872
number of last returns:         682155
number of single returns:       508548
overview over number of returns of given pulse: 508548 334560 20380 176 0 0 0
histogram of classification of points:
          130215  ground (2)
          382700  low vegetation (3)
          258700  medium vegetation (4)
           92049  high vegetation (5)
gps_time histogram with bin size 1.000000
  bin 517976 has 11327
  bin 517977 has 44963
  bin 517978 has 76977
  bin 517979 has 86054
  bin 517980 has 74027
  bin 517981 has 43853
  bin 517982 has 10667
  bin 518288 has 107
  bin 519683 has 33
  bin 519684 has 30823
  bin 519685 has 86390
  bin 519686 has 139623
  bin 519687 has 138507
  bin 519688 has 87262
  bin 519689 has 32833
  bin 519690 has 218
  average gps_time 518999.07597545238 for 863664 element(s)
las_file_with_duplicate_shifted_returns.jpg

Dennis Bernardi

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Nov 27, 2018, 11:50:56 AM11/27/18
to last...@googlegroups.com

Thank you very much

 

 

Dennis Bernardi

Coordenador Corporativo

Cadastro e Geoprocessamento

dennis....@fibria.com.br

Cel 55 12  99704 5301

cid:image001.jpg@01CDD786.860079A0

Tel 55 12 2128 1480

______________________________

 

www.fibria.com.br

 

De: last...@googlegroups.com [mailto:last...@googlegroups.com] Em nome de Martin Isenburg
Enviada em: terça-feira, 27 de novembro de 2018 11:42
Para: last...@googlegroups.com
Assunto: Re: [LAStools] Validade .LAS files

 

#Atenção, este é um e-mail externo#

Tel 55 12 2128 1480

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