# 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`:

    1pdal density ./exercises/analysis/density/uncompahgre.laz  \
    2-o ./exercises/analysis/density/density.sqlite \
    3-f SQLite

    1pdal density ./exercises/analysis/density/uncompahgre.laz  ^
    2-o ./exercises/analysis/density/density.sqlite ^
    3-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.