1.. _density: 2 3Visualizing acquisition density 4================================================================================ 5 6.. include:: ../../../includes/substitutions.rst 7 8.. index:: Density, OGR, hexagon tessellation 9 10This exercise uses PDAL to generate a density surface. You can use this 11surface to summarize acquisition quality. 12 13 14Exercise 15-------------------------------------------------------------------------------- 16 17PDAL provides an :ref:`application <density_command>` to compute a vector 18field of hexagons computed with :ref:`filters.hexbin`. It is a kind of 19simple interpolation, which we will use for visualization in |QGIS|. 20 21 22Command 23................................................................................ 24 25Invoke the following command, substituting accordingly, in your ` Shell`: 26 27.. literalinclude:: ./density-command.txt 28 :linenos: 29 30.. literalinclude:: ./density-command-win.txt 31 :linenos: 32 33 34.. image:: ../../../images/density-command-run.png 35 :target: ../../../../_images/density-command-run.png 36 37Visualization 38................................................................................ 39 40The command uses GDAL to output a `SQLite`_ file containing hexagon polygons. 41We will now use |QGIS| to visualize them. 42 43.. _`SQLite`: http://sqlite.org 44 45 461. Add a vector layer 47 48 .. image:: ../../../images/density-add-layer.png 49 :target: ../../../../_images/density-add-layer.png 50 512. Navigate to the output directory 52 53 .. image:: ../../../images/density-select-layer.png 54 :target: ../../../../_images/density-select-layer.png 55 563. Add the ``density.sqlite`` file to the view 57 58 .. image:: ../../../images/density-file-open.png 59 :target: ../../../../_images/density-file-open.png 60 614. Right click on the ``density.sqlite`` layer in the `Layers` panel 62 and then choose ``Properties``. 63 645. Pick the ``Graduated`` drop down 65 66 .. image:: ../../../images/density-graduated-symbols-pick.png 67 :target: ../../../../_images/density-graduated-symbols-pick.png 68 696. Choose the ``Count`` column to visualize 70 71 .. image:: ../../../images/density-count-attribute.png 72 :target: ../../../../_images/density-count-attribute.png 73 747. Choose the ``Classify`` button to add intervals 75 76 .. image:: ../../../images/density-graduated-symbols.png 77 :target: ../../../../_images/density-Graduated-symbols.png 78 798. Adjust the visualization as desired 80 81 .. image:: ../../../images/density-final-render.png 82 :target: ../../../../_images/density-final-render.png 83 84Notes 85-------------------------------------------------------------------------------- 86 87 881. You can control how the density hexagon surface is created by 89 using the options in :ref:`filters.hexbin`. 90 91 The following settings will use a hexagon edge size of 24 92 units. 93 94 :: 95 96 --filters.hexbin.edge_size=24 97 982. You can generate a contiguous boundary using |PDAL|'s :ref:`tindex_command`. 99 100.. _`Uncompahgre Basin`: https://en.wikipedia.org/wiki/Uncompahgre_River 101