Visualizing acquisition density

This exercise uses PDAL to generate a density surface. You can use this surface to summarize acquisition quality.

Exercise

PDAL provides an application to compute a vector field of hexagons computed with filters.hexbin. It is a kind of simple interpolation, which we will use for visualization in QGIS.

Command

Invoke the following command, substituting accordingly, in your OSGeo4W Shell:

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pdal density ^
   c:/Users/hobu/PDAL/exercises/analysis/density/uncompahgre.laz ^
   -o c:/Users/hobu/PDAL/exercises/analysis/density/density.sqlite ^
   -f SQLite
../../../../_images/density-command-run.png

Visualization

The command uses GDAL to output a SQLite file containing hexagon polygons. We will now use QGIS to visualize them.

  1. Add a vector layer

    ../../../../_images/density-add-layer1.png
  2. Navigate to the output directory

    ../../../../_images/density-select-layer.png
  3. Add the density.sqlite file to the view

    ../../../../_images/density-file-open.png
  4. Right click on the density.sqlite layer in the Layers panel and then choose Properties.

  5. Pick the Graduated drop down

    ../../../../_images/density-graduated-symbols-pick.png
  6. Choose the Count column to visualize

    ../../../../_images/density-count-attribute.png
  7. Choose the Classify button to add intervals

    ../../../../_images/density-graduated-symbols.png
  8. Adjust the visualization as desired

    ../../../../_images/density-final-render.png

Notes

  1. You can control how the density hexagon surface is created by using the options in filters.hexbin.

    The following settings will use a hexagon edge size of 24 units.

    --filters.hexbin.edge_size=24
    
  2. You can generate a contiguous boundary using PDAL’s tindex.