filters.reprojection

The reprojection filter converts the X, Y and/or Z dimensions to a new spatial reference system. The old coordinates are replaced by the new ones, if you want to preserve the old coordinates for future processing, use a filters.ferry to create a new dimension and stuff them there.

Note

X, Y, and Z dimensions in PDAL are carried as doubles, with their scale information applied. Set the output scale (scale_x, scale_y, or scale_z) on your writer to descale the data on the way out.

Many LIDAR formats store coordinate information in 32-bit address spaces, and use scaling and offsetting to ensure that accuracy is not lost while fitting the information into a limited address space. When changing projections, the coordinate values will change, which may change the optimal scale and offset for storing the data.

Example 1

This pipeline reprojecs terrain points with Z-values between 0 and 100 by first applying a range filter and then specifing both the input and output spatial reference as EPSG-codes. The X and Y dimensions are scaled to allow enough precision in the output coordinates.

{
  "pipeline":[
    {
      "filename":"input.las",
      "type":"readers.las",
      "spatialreference":"EPSG:26916"
    },
    {
      "type":"filters.range",
      "limits":"Z[0:100],Classification[2:2]"
    },
    {
      "type":"filters.reprojection",
      "in_srs":"EPSG:26916",
      "out_srs":"EPSG:4326"
    },
    {
      "type":"writers.las",
      "scale_x":"0.0000001",
      "scale_y":"0.0000001",
      "scale_z":"0.01",
      "offset_x":"auto",
      "offset_y":"auto",
      "offset_z":"auto",
      "filename":"example-geog.las"
    }
  ]
}

Example 2

In some cases it is not possible to use a EPSG-code as a spatial reference. Instead Proj.4 parameters can be used to define a spatial reference. In this example the vertical component of points in a laz file is converted from geometric (ellipsoidal) heights to orthometric heights by using the geoidgrids parameter from Proj.4. Here we change the vertical datum from the GRS80 ellipsoid to DVR90, the vertical datum in Denmark. In the writing stage of the pipeline the spatial reference of the file is set to EPSG:7416. The last step is needed since PDAL will otherwise reference the vertical datum as “Unnamed Vertical Datum” in the spatial reference VLR.

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{
  "pipeline":[
    "./1km_6135_632.laz",
    {
        "type":"filters.reprojection",
        "in_srs":"EPSG:25832",
        "out_srs":"+init=epsg:25832 +geoidgrids=C:/data/geoids/dvr90.gtx"
    },
    {
      "type":"writers.las",
      "a_srs":"EPSG:7416",
      "filename":"1km_6135_632_DVR90.laz"
    }
  ]
}

Options

in_srs
Spatial reference system of the input data. Express as an EPSG string (eg “EPSG:4326” for WGS84 geographic), Proj.4 string or a well-known text string. [Required if input reader does not supply SRS information]
out_srs
Spatial reference system of the output data. Express as an EPSG string (eg “EPSG:4326” for WGS84 geographic), Proj.4 string or a well-known text string. [Required]