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 ` Shell`:

$ pdal density ./exercises/analysis/density/uncompahgre.laz  \
-o ./exercises/analysis/density/density.sqlite \
-f SQLite

> pdal density ./exercises/analysis/density/uncompahgre.laz  ^
-o ./exercises/analysis/density/density.sqlite ^
-f SQLite

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

   

2. Navigate to the output directory

   

3. Add the density.sqlite file to the view

   

4. Right click on the density.sqlite layer in the Layers panel and then choose Properties.

5. Pick the Graduated drop down

   

6. Choose the Count column to visualize

   

7. Choose the Classify button to add intervals

   

8. Adjust the visualization as desired

   

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.