Use PDAL to create a ground surface model from point cloud input

pipeline.hjson

# This is a hjson file, https://hjson.org/
# Linux bash
#GET=https://github.com/hjson/hjson-go/releases/download/v3.0.0/linux_amd64.tar.gz
# macOS bash
#GET=https://github.com/hjson/hjson-go/releases/download/v3.0.0/darwin_amd64.tar.gz
# Install
#curl -sSL $GET | sudo tar -xz -C /usr/local/bin
# Translate to Json
#hjson -j pipeline.hjson > pipeline.json
#pdal pipeline pipeline.json --verbose 8

{
  pipeline:
  [
# Input
    {
      # read from our ept server
      # up to 0.5m resolutions
      # type: readers.ept
      # bounds: ([802000, 802500], [2493000, 2493500])
      # filename: http://localhost:8080/ept.json
      filename: red-rocks.laz
      # filename: http://na.entwine.io/red-rocks/ept.json
      # resolution: 0.5
    }
#     {
#       # read from our las file
#       type: readers.las
#       filename: small500-no-outliers.laz
#     }


# Filters
    {
      # adds a classification value of 7 to the noise points
      type: filters.outlier
      # method: radius
      # radius: 1.0
      # min_k: 8 # min number of neighbors in radius

      method: statistical
      mean_k: 8
      multiplier: 3

    }

    {
      # voxel-based sampling filter
      # reduce the size of the pc
      # cell size of 0.2 meters in xyz
      type: filters.voxelcenternearestneighbor
      cell: 0.1
    }

    {
      # Need to assign point cloud dimension NumberOfReturns 1
      # Otherwise: "No returns to process."
        type:filters.assign
        assignment : NumberOfReturns[0:0]=1
    }

    {
      # Ground classification, ignore the noise points
      type: filters.smrf
      ignore:Classification[7:7]
    }

    {
      # only allow ground classified points
      type: filters.range
      limits: Classification[2:2]
    }

    {
      # OPTIONAL
      # turn this into a DEM 3D model
      # do not use multiple types
      # type: filters.delaunay
      type: filters.poisson
    }


# Output

# # OPTIONAL PLY IF DEM
    {
      # write to ply
      type:writers.ply
      filename: red-rocks-smrf-only-poisson.ply
      faces:true
      storage_mode: default
    }
# Output
    # {
    #   # write to laz
    #   type:writers.las
    #   filename: red-rocks-ground.laz
    # }
  ]
}

ctmconv red-rocks-smrf-only-delaunay.ply red-rocks-smrf-only-delaunay.stl can convert ply to stl
ctmviewer red-rocks-smrf-only-delaunay.ply visualizes the ply.

sudo apt install openctm-tools