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.. _voxelgrid:
Downsampling a PointCloud using a VoxelGrid filter
--------------------------------------------------
In this tutorial we will learn how to downsample -- that is, reduce the number
of points -- a point cloud dataset, using a voxelized grid approach.
The ``VoxelGrid`` class that we're about to present creates a *3D voxel grid*
(think about a voxel grid as a set of tiny 3D boxes in space) over the input
point cloud data. Then, in each *voxel* (i.e., 3D box), all the points present
will be approximated (i.e., *downsampled*) with their centroid. This approach
is a bit slower than approximating them with the center of the voxel, but it
represents the underlying surface more accurately.
.. raw:: html
<iframe title="Downsampling a PointCloud using a VoxelGrid filter" width="480" height="390" src="http://www.youtube.com/embed/YHR6_OIxtFI?rel=0" frameborder="0" allowfullscreen></iframe>
The code
--------
First, download the dataset `table_scene_lms400.pcd
<https://raw.github.com/PointCloudLibrary/data/master/tutorials/table_scene_lms400.pcd>`_
and save it somewhere to disk.
Then, create a file, let's say, ``voxel_grid.cpp`` in your favorite
editor, and place the following inside it:
.. literalinclude:: sources/voxel_grid/voxel_grid.cpp
:language: cpp
:linenos:
The explanation
---------------
Now, let's break down the code piece by piece.
The following lines of code will read the point cloud data from disk.
.. literalinclude:: sources/voxel_grid/voxel_grid.cpp
:language: cpp
:lines: 12-15
Then, a *pcl::VoxelGrid* filter is created with a leaf size of 1cm, the input
data is passed, and the output is computed and stored in *cloud_filtered*.
.. literalinclude:: sources/voxel_grid/voxel_grid.cpp
:language: cpp
:lines: 21-24
Finally, the data is written to disk for later inspection.
.. literalinclude:: sources/voxel_grid/voxel_grid.cpp
:language: cpp
:lines: 29-31
Compiling and running the program
---------------------------------
Add the following lines to your CMakeLists.txt file:
.. literalinclude:: sources/voxel_grid/CMakeLists.txt
:language: cmake
:linenos:
After you have made the executable, you can run it. Simply do::
$ ./voxel_grid
You will see something similar to::
PointCloud before filtering: 460400 data points (x y z intensity distance sid).
PointCloud after filtering: 41049 data points (x y z intensity distance sid).
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