[pdal] FW: LAS Files Reclassifying Points with Flags - pdal info query + differences between pdal info / lasinfo classification outputs (fixed typo)

[Rose Phillips]

Hi guys,

Hope you're all having a good week.
When reclassifying points in LAS files where there are also flags (withheld, synthetic, keypoint or overlap), I've noticed a discrepancy between pdal info + lasinfo reports with my output LAS files, and an assortment of classification codes (for pdal info) that I'm not familiar with.

I used pdal pipeline to reclassify points under code 10 to 17 :-


{
  "pipeline" : [
   {
        "type" : "readers.las",
        "filename" : "input.las"
   },
    {
        "type":"filters.assign",
        "assignment":"Classification[10:10]=17"
    },
    {
        "type" : "writers.las",
        "minor_version" : 4,
        "dataformat_id": 1,
        "a_srs" : "EPSG:2193+7839",
        "forward" : "all",
        "filename" : "output.las"
    }
  ]
}


Looking at lasinfo reports, for an input and output file, it looks like there are still points assigned as 17? But the pdal info reports show something else, and points with different counts e.g.

Input file (pdal info)
  "filename": "D:\\ BM34_2018_1000_1637.las",
  "pdal_version": "2.0.1 (git-version: Release)",
  "stats":
  {
    "statistic":
    [
      {
        "average": 38.90448897,
        "count": 4048726,
        "counts":
        [
          "1.000000/1",
          "2.000000/2590331",
          "3.000000/146834",
          "4.000000/16873",
          "5.000000/106701",
          "6.000000/13937",
          "7.000000/51",
          "9.000000/14124",
          "10.000000/218",
          "130.000000/993308",
          "131.000000/102834",
          "132.000000/6622",
          "133.000000/40561",
          "134.000000/9820",
          "135.000000/5",
          "137.000000/6215",
          "138.000000/291"
        ],
        "maximum": 138,
        "minimum": 1,
        "name": "Classification",
        "position": 0,
        "stddev": 57.89674269,
        "variance": 3352.032814
      }
    ]
  }
}

Output File (pdal info)
{
  "filename": "D:\\palmerston_north_cc\\pdal_reclassification_issue\\reclassified\\CL2_BM34_2018_1000_1637.laz",
  "pdal_version": "2.0.1 (git-version: Release)",
  "stats":
  {
    "statistic":
    [
      {
        "average": 38.90486588,
        "count": 4048726,
        "counts":
        [
          "1.000000/1",
          "2.000000/2590331",
          "3.000000/146834",
          "4.000000/16873",
          "5.000000/106701",
          "6.000000/13937",
          "7.000000/51",
          "9.000000/14124",
          "17.000000/218",
          "130.000000/993308",
          "131.000000/102834",
          "132.000000/6622",
          "133.000000/40561",
          "134.000000/9820",
          "135.000000/5",
          "137.000000/6215",
          "138.000000/291"
        ],
        "maximum": 138,
        "minimum": 1,
        "name": "Classification",
        "position": 0,
        "stddev": 57.8965773,
        "variance": 3352.013663
      }
    ]
  }
}

Input file (lasinfo)

histogram of classification of points:
               1  unclassified (1)
         3583639  ground (2)
          249668  low vegetation (3)
           23495  medium vegetation (4)
          147262  high vegetation (5)
           23757  building (6)
              56  noise (7)
           20339  water (9)
             509  rail (10)
+-> flagged as withheld:  1159656

Output file (lasinfo)

histogram of classification of points:
               1  unclassified (1)
         3583639  ground (2)
          249668  low vegetation (3)
           23495  medium vegetation (4)
          147262  high vegetation (5)
           23757  building (6)
              56  noise (7)
           20339  water (9)
             291  rail (10)
             218  bridge deck (17)
+-> flagged as withheld:  1159656


I'm guessing pdal info is the most accurate output as arcgis pro + global mapper outputs are the same as pdal info and lasinfo is the odd one out.
I wrote a las2las and pdal pipeline workaround to make sure that both lasinfo + pdal info outputs were the same.

I was wondering if you guys knew why the flags were written as numbers and why they are split up in codes, that change for each file?

Many thanks and kind regards,
Rose Phillips

Location Data Analyst
Land Information New Zealand


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