filters.hexbin¶

A common questions for users of point clouds is what the spatial extent of a point cloud collection is. Files generally provide only rectangular bounds, but often the points inside the files only fill up a small percentage of the area within the bounds.

Hexbin output shows boundary of actual points in point buffer, not just rectangular extents.

The hexbin filter reads a point stream and writes out a metadata record that contains a much tighter data bound, expressed as a well-known text polygon. In order to write out the metadata record, the pdal pipeline command must be invoked using the –pipeline-serialization option:

$ pdal hexbin-pipeline.xml --pipeline-serialization hexbin-out.xml

After running with the pipeline serialization option, the output file looks like this:

<PointView>
  <Metadata name="pointbuffer" type="blank">
    <Metadata name="filters.hexbin" type="blank">
      <Metadata name="edge_size" type="double">
        0.002218331916495204
      </Metadata>
      <Metadata name="threshold" type="nonNegativeInteger">
        15
      </Metadata>
      <Metadata name="sample_size" type="nonNegativeInteger">
        5000
      </Metadata>
      <Metadata name="boundary" type="string">
        MULTIPOLYGON (((
        -80.8466 35.2183, -80.8460 35.2194,
        -80.8447 35.2194, -80.8441 35.2205,
        -80.8428 35.2205, -80.8421 35.2216,
        ...
        -80.8498 35.2194, -80.8486 35.2194,
        -80.8479 35.2183, -80.8466 35.2183
        )))
      </Metadata>
    </Metadata>
  </Metadata>
</PointView>

In addition, if you have defined a writer you will have the usual point data output file.

Example¶

<?xml version="1.0" encoding="utf-8"?>
<Pipeline version="1.0">
  <Writer type="writers.las">
    <Option name="filename">
      file-output.las
    </Option>
    <Filter type="filters.hexbin">
      <Option name="threshold">10</Option>
      <Reader type="readers.las">
        <Option name="filename">
          file-input.las
        </Option>
      </Reader>
    </Filter>
  </Writer>
</Pipeline>

Options¶

edge_size: If not set, the hexbin filter will estimate a hex size based on a sample of the data. If set, hexbin will use the provided size in constructing the hexbins to test.
sample_size: How many points to sample when automatically calculating the edge size? [Default: 5000]
threshold: Number of points that have to fall within a hexbin before it is considered “in” the data set. [Default: 15]
precision: Coordinate precision to use in writing out the well-known text of the boundary polygon. [Default: 8]