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Re-saving LAS file removes meta-data (.las .laz) #515

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dbworth opened this Issue Mar 3, 2017 · 5 comments

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@dgirardeau dgirardeau

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@dbworth @dgirardeau
@dbworth

dbworth commented Mar 3, 2017

Thanks for the great open-source tool!

Current Behavior

When I open a .las file in CloudCompare and then immediately re-save the cloud as a .las file, lots of the meta-data is removed with no warning.
For example, if the .las file was georeferenced with a datum (e.g. "this is my location in the world"), this is removed and this affects processing files for GIS applications.

Expected Behavior

The header and meta-data should be written back out again, the same.

Steps to Reproduce

To verify this you need a geo-tagged LiDAR cloud from the DEM section here: https://earthexplorer.usgs.gov/
I can upload a sample file somewhere if you like.

For the original file, use the lasinfo tool (http://lastools.org/download/LAStools.zip) to view the meta-data. Then load the .las file in CloudCompare and re-save it. Use lasinfo again to see the meta-data has been changed.

Below is included a full screen dump.

Context/Comments

I'm not sure what LAS library is being used. Perhaps at a minimum, CloudCompare should warn "stripping LAS meta-data".
A nice example is MeshLab that when you re-save a mesh file, it prompts you for Binary VS. ASCII, Color Vs. no-color, etc.

Your Environment

Windows 7 64-bit.
CloudCompare 2.8 beta

.

This is the meta-data of original file

>lasinfo PA_Statewide_S_2006-2008_003435.las

lasinfo (161016) report for PA_Statewide_S_2006-2008_003435.las
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:        1.1
  system identifier:          'NIIRS10'
  generating software:        'LIDAR1 tiled'
  file creation day/year:     270/2008
  header size:                227
  offset to point data:       2103
  number var. length records: 5
  point data format:          1
  point data record length:   28
  number of point records:    3555744
  number of points by return: 0 0 0 0 0
  scale factor x y z:         0.01 0.01 0.01
  offset x y z:               0 0 0
  min x y z:                  1360000.01 410000.01 799.74
  max x y z:                  1370000.00 420000.00 1231.85
variable length header record 1 of 5:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34735
  length after header  192
  description          'GeoTiff Projection Keys'
    GeoKeyDirectoryTag version 1.1.0 number of keys 23
      key 1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: M
odelTypeProjected
      key 2048 tiff_tag_location 0 count 1 value_offset 4269 - GeographicTypeGeo
Key: GCS_NAD83
      key 2049 tiff_tag_location 34737 count 24 value_offset 54 - GeogCitationGe
oKey: GCS_North_American_1983
      key 2050 tiff_tag_location 0 count 1 value_offset 6269 - GeogGeodeticDatum
GeoKey: Datum_North_American_Datum_1983
      key 2051 tiff_tag_location 0 count 1 value_offset 8901 - GeogPrimeMeridian
GeoKey: PM_Greenwich
      key 2054 tiff_tag_location 0 count 1 value_offset 9102 - GeogAngularUnitsG
eoKey: Angular_Degree
      key 2055 tiff_tag_location 34736 count 1 value_offset 11 - GeogAngularUnit
SizeGeoKey: 0.01745329252
      key 2056 tiff_tag_location 0 count 1 value_offset 7019 - GeogEllipsoidGeoK
ey: Ellipse_GRS_1980
      key 2057 tiff_tag_location 34736 count 1 value_offset 8 - GeogSemiMajorAxi
sGeoKey: 6378137
      key 2059 tiff_tag_location 34736 count 1 value_offset 9 - GeogInvFlattenin
gGeoKey: 298.2572221
      key 2061 tiff_tag_location 34736 count 1 value_offset 10 - GeogPrimeMeridi
anLongGeoKey: 0
      key 3072 tiff_tag_location 0 count 1 value_offset 32129 - ProjectedCSTypeG
eoKey: NAD83 / Pennsylvania South
      key 3073 tiff_tag_location 34737 count 54 value_offset 0 - PCSCitationGeoK
ey: NAD_1983_StatePlane_Pennsylvania_South_FIPS_3702_Feet
      key 3075 tiff_tag_location 0 count 1 value_offset 8 - ProjCoordTransGeoKey
: CT_LambertConfConic_2SP
      key 3076 tiff_tag_location 0 count 1 value_offset 9003 - ProjLinearUnitsGe
oKey: Linear_Foot_US_Survey
      key 3077 tiff_tag_location 34736 count 1 value_offset 7 - ProjLinearUnitSi
zeGeoKey: 0.3048006096
      key 3078 tiff_tag_location 34736 count 1 value_offset 3 - ProjStdParallel1
GeoKey: 39.93333333
      key 3079 tiff_tag_location 34736 count 1 value_offset 4 - ProjStdParallel2
GeoKey: 40.96666667
      key 3081 tiff_tag_location 34736 count 1 value_offset 6 - ProjNatOriginLat
GeoKey: 39.33333333
      key 3082 tiff_tag_location 34736 count 1 value_offset 0 - ProjFalseEasting
GeoKey: 1968500
      key 3083 tiff_tag_location 34736 count 1 value_offset 1 - ProjFalseNorthin
gGeoKey: 0
      key 3088 tiff_tag_location 34736 count 1 value_offset 2 - ProjCenterLongGe
oKey: -77.75
      key 3093 tiff_tag_location 34736 count 1 value_offset 5 - ProjScaleAtCente
rGeoKey: 0
variable length header record 2 of 5:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34736
  length after header  96
  description          'GeoTiff double parameters'
    GeoDoubleParamsTag (number of doubles 12)
      1.9685e+006 0 -77.75 39.9333 40.9667 0 39.3333 0.304801 6.37814e+006 298.2
57 0 0.0174533
variable length header record 3 of 5:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34737
  length after header  78
  description          'GeoTiff ASCII parameters'
    GeoAsciiParamsTag (number of characters 78)
      NAD_1983_StatePlane_Pennsylvania_South_FIPS_3702_Feet|GCS_North_American_1
983|
variable length header record 4 of 5:
  reserved             43707
  user ID              'NIIRS10'
  record ID            4
  length after header  10
  description          'NIIRS10 Timestamp'
variable length header record 5 of 5:
  reserved             43707
  user ID              'NIIRS10'
  record ID            1
  length after header  26
  description          'NIIRS10 Tile Index'
the header is followed by 1204 user-defined bytes
reporting minimum and maximum for all LAS point record entries ...
  X           136000001  137000000
  Y            41000001   42000000
  Z               79974     123185
  intensity           0        255
  return_number       1          2
  number_of_returns   1          2
  edge_of_flight_line 0          0
  scan_direction_flag 0          0
  classification      1         15
  scan_angle_rank     0          0
  user_data           0          0
  point_source_ID    52         55
  gps_time 0.000000 0.000000
number of first returns:        2994245
number of intermediate returns: 0
number of last returns:         2957224
number of single returns:       2395725
WARNING: for return 1 real number of points by return is 2994245 but header entr
y was not set.
WARNING: for return 2 real number of points by return is 561499 but header entry
 was not set.
overview over number of returns of given pulse: 2395725 1160019 0 0 0 0 0
histogram of classification of points:
         1075294  unclassified (1)
         1496896  ground (2)
          317693  keypoint (8)
             355  water (9)
          598520  overlap (12)
           66986  tower (15)

.

This is the meta-data of the file re-saved with CloudCompare


>lasinfo PA_Statewide_S_2006-2008_003435_resaved.las

lasinfo (161016) report for PA_Statewide_S_2006-2008_003435_resaved.las
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:          'libLAS'
  generating software:        'libLAS 1.8.0'
  file creation day/year:     61/2017
  header size:                227
  offset to point data:       227
  number var. length records: 0
  point data format:          3
  point data record length:   34
  number of point records:    3555744
  number of points by return: 0 0 0 0 0
  scale factor x y z:         0.01 0.01 0.01
  offset x y z:               1360000.0099999998 410000.009765625 799.7399902343
75
  min x y z:                  1360000.01 410000.01 799.74
  max x y z:                  1370000.00 420000.00 1231.85
reporting minimum and maximum for all LAS point record entries ...
  X                   0     999999
  Y                   0     999999
  Z                   0      43211
  intensity           0        255
  return_number       1          2
  number_of_returns   1          2
  edge_of_flight_line 0          0
  scan_direction_flag 0          0
  classification      1         15
  scan_angle_rank     0          0
  user_data           0          0
  point_source_ID    52         55
  gps_time 0.000000 0.000000
  Color R 0 0
        G 0 0
        B 0 0
number of first returns:        2994245
number of intermediate returns: 0
number of last returns:         2957224
number of single returns:       2395725
WARNING: for return 1 real number of points by return is 2994245 but header entr
y was not set.
WARNING: for return 2 real number of points by return is 561499 but header entry
 was not set.
overview over number of returns of given pulse: 2395725 1160019 0 0 0 0 0
histogram of classification of points:
         1075294  unclassified (1)
         1496896  ground (2)
          317693  keypoint (8)
             355  water (9)
          598520  overlap (12)
           66986  tower (15)
@dgirardeau
Owner

dgirardeau commented Mar 4, 2017

Indeed, CC doesn't handle LAS meta-data at all. We use libLAS (for now), but I don't know how easy to extract or push these pieces of information when loading and saving a file.

I'll see what I can do, otherwise I'll add a warning message as suggested.

dgirardeau self-assigned this Mar 4, 2017

dgirardeau added the enhancement label Mar 4, 2017

@dgirardeau
Owner

dgirardeau commented Mar 5, 2017

I've updated the online 2.9 beta version: the 'Spatial Reference System' (SRS) of the LAS file is now saved as meta-data and exported (if available) when saving the cloud as a new file.

I'm just not sure that the SRS contains everything... Can you test it on your side and see if any important stuff is missing?
@dgirardeau
Owner

dgirardeau commented Mar 6, 2017

Note that I uploaded the wrong version yesterday ;). It's should now be ok.
@dbworth

dbworth commented Mar 8, 2017

Thanks for your quick response, that's great. It works nicely. :-)

Long answer:
I tried the 2.9 beta with Windows 64-bit.
I opened an aerial LiDAR tile in .las format in CloudCompare,
then did a small segment (crop) operation,
then re-saved as a .las file.

Then I opened the .las file in another program (e.g. QGIS) and it is shown correctly, and in the right location of the world.

Also I was able to merge (combine) two LiDAR tiles using CloudCompare, and then save them as one .las file with the correct geo-reference data.

.

How to merge LiDAR tiles with GeoTIFF data:

My guess is that this will only work if the tiles have the same datum/projection, are are simply offset from each other.

Drag the two .las files into CloudCompare, which loads them in their correct relative location next to each other:
01_open_lidar_tiles

Drag the cloud from one object into the other:
02_put_clouds_together

Select both clouds and use the merge tool:
03_merge_clouds

Re-save the merged cloud as a .las file:
04_final_cloud

Done!

.

Also, here is the meta-data that CloudCompare 2.9 beta writes out when saving a .las file.
It's not all the meta-data, but at least it includes the GeoTIFF tags, which contains the global location and projection information:

>lasinfo PA_Statewide_S_2006-2008_003435_resaved_new_Beta.las

lasinfo (161016) report for temp_resaved.las
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:          'libLAS'
  generating software:        'libLAS 1.8.0'
  file creation day/year:     65/2017
  header size:                227
  offset to point data:       755
  number var. length records: 3
  point data format:          3
  point data record length:   34
  number of point records:    3409902
  number of points by return: 0 0 0 0 0
  scale factor x y z:         0.01 0.01 0.01
  offset x y z:               1350000.0099999998 410000.009765625 709.3300170898
4375
  min x y z:                  1350000.01 410000.01 709.33
  max x y z:                  1360000.00 420000.00 1762.37
variable length header record 1 of 3:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34735
  length after header  192
  description          'GeoTiff Projection Keys'
    GeoKeyDirectoryTag version 1.1.0 number of keys 23
      key 1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: M
odelTypeProjected
      key 2048 tiff_tag_location 0 count 1 value_offset 4269 - GeographicTypeGeo
Key: GCS_NAD83
      key 2049 tiff_tag_location 34737 count 24 value_offset 54 - GeogCitationGe
oKey: GCS_North_American_1983
      key 2050 tiff_tag_location 0 count 1 value_offset 6269 - GeogGeodeticDatum
GeoKey: Datum_North_American_Datum_1983
      key 2051 tiff_tag_location 0 count 1 value_offset 8901 - GeogPrimeMeridian
GeoKey: PM_Greenwich
      key 2054 tiff_tag_location 0 count 1 value_offset 9102 - GeogAngularUnitsG
eoKey: Angular_Degree
      key 2055 tiff_tag_location 34736 count 1 value_offset 11 - GeogAngularUnit
SizeGeoKey: 0.01745329252
      key 2056 tiff_tag_location 0 count 1 value_offset 7019 - GeogEllipsoidGeoK
ey: Ellipse_GRS_1980
      key 2057 tiff_tag_location 34736 count 1 value_offset 8 - GeogSemiMajorAxi
sGeoKey: 6378137
      key 2059 tiff_tag_location 34736 count 1 value_offset 9 - GeogInvFlattenin
gGeoKey: 298.2572221
      key 2061 tiff_tag_location 34736 count 1 value_offset 10 - GeogPrimeMeridi
anLongGeoKey: 0
      key 3072 tiff_tag_location 0 count 1 value_offset 32129 - ProjectedCSTypeG
eoKey: NAD83 / Pennsylvania South
      key 3073 tiff_tag_location 34737 count 54 value_offset 0 - PCSCitationGeoK
ey: NAD_1983_StatePlane_Pennsylvania_South_FIPS_3702_Feet
      key 3075 tiff_tag_location 0 count 1 value_offset 8 - ProjCoordTransGeoKey
: CT_LambertConfConic_2SP
      key 3076 tiff_tag_location 0 count 1 value_offset 9003 - ProjLinearUnitsGe
oKey: Linear_Foot_US_Survey
      key 3077 tiff_tag_location 34736 count 1 value_offset 7 - ProjLinearUnitSi
zeGeoKey: 0.3048006096
      key 3078 tiff_tag_location 34736 count 1 value_offset 3 - ProjStdParallel1
GeoKey: 39.93333333
      key 3079 tiff_tag_location 34736 count 1 value_offset 4 - ProjStdParallel2
GeoKey: 40.96666667
      key 3081 tiff_tag_location 34736 count 1 value_offset 6 - ProjNatOriginLat
GeoKey: 39.33333333
      key 3082 tiff_tag_location 34736 count 1 value_offset 0 - ProjFalseEasting
GeoKey: 1968500
      key 3083 tiff_tag_location 34736 count 1 value_offset 1 - ProjFalseNorthin
gGeoKey: 0
      key 3088 tiff_tag_location 34736 count 1 value_offset 2 - ProjCenterLongGe
oKey: -77.75
      key 3093 tiff_tag_location 34736 count 1 value_offset 5 - ProjScaleAtCente
rGeoKey: 0
variable length header record 2 of 3:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34736
  length after header  96
  description          'GeoTiff double parameters'
    GeoDoubleParamsTag (number of doubles 12)
      1.9685e+006 0 -77.75 39.9333 40.9667 0 39.3333 0.304801 6.37814e+006 298.2
57 0 0.0174533
variable length header record 3 of 3:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34737
  length after header  78
  description          'GeoTiff ASCII parameters'
    GeoAsciiParamsTag (number of characters 78)
      NAD_1983_StatePlane_Pennsylvania_South_FIPS_3702_Feet|GCS_North_American_1
983|
reporting minimum and maximum for all LAS point record entries ...
  X                   0     999999
  Y                   0     999999
  Z                   0     105304
  intensity           0        255
  return_number       1          2
  number_of_returns   1          2
  edge_of_flight_line 0          0
  scan_direction_flag 0          0
  classification      1         15
  scan_angle_rank     0          0
  user_data           0          0
  point_source_ID    52         55
  gps_time 0.000000 0.000000
  Color R 0 0
        G 0 0
        B 0 0
number of first returns:        2973320
number of intermediate returns: 0
number of last returns:         2945605
number of single returns:       2509023
WARNING: for return 1 real number of points by return is 2973320 but header entr
y was not set.
WARNING: for return 2 real number of points by return is 436582 but header entry
 was not set.
overview over number of returns of given pulse: 2509023 900879 0 0 0 0 0
histogram of classification of points:
         1135712  unclassified (1)
         1411257  ground (2)
          336295  keypoint (8)
             372  water (9)
          464297  overlap (12)
           61969  tower (15)

I'm happy for this issue to be closed.
@dgirardeau
Owner

dgirardeau commented Mar 8, 2017

Great. Thanks for the feedback!

dgirardeau closed this Mar 8, 2017

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