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thirdParty (VzNLSDK, PCL 1.12.0, opencv) initial check in
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<li><a class="reference internal" href="#">Downsampling a PointCloud using a VoxelGrid filter</a></li>
<li><a class="reference internal" href="#the-code">The code</a></li>
<li><a class="reference internal" href="#the-explanation">The explanation</a></li>
<li><a class="reference internal" href="#compiling-and-running-the-program">Compiling and running the program</a></li>
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<div class="section" id="downsampling-a-pointcloud-using-a-voxelgrid-filter">
<span id="voxelgrid"></span><h1>Downsampling a PointCloud using a VoxelGrid filter</h1>
<p>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.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">VoxelGrid</span></code> class that we’re about to present creates a <em>3D voxel grid</em>
(think about a voxel grid as a set of tiny 3D boxes in space) over the input
point cloud data. Then, in each <em>voxel</em> (i.e., 3D box), all the points present
will be approximated (i.e., <em>downsampled</em>) 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.</p>
<iframe title="Downsampling a PointCloud using a VoxelGrid filter" width="480" height="390" src="https://www.youtube.com/embed/YHR6_OIxtFI?rel=0" frameborder="0" allowfullscreen></iframe></div>
<div class="section" id="the-code">
<h1>The code</h1>
<p>First, download the dataset <a class="reference external" href="https://raw.github.com/PointCloudLibrary/data/master/tutorials/table_scene_lms400.pcd">table_scene_lms400.pcd</a>
and save it somewhere to disk.</p>
<p>Then, create a file, let’s say, <code class="docutils literal notranslate"><span class="pre">voxel_grid.cpp</span></code> in your favorite
editor, and place the following inside it:</p>
<div class="highlight-cpp notranslate"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre> 1
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34</pre></div></td><td class="code"><div class="highlight"><pre><span></span><span class="cp">#include</span> <span class="cpf">&lt;iostream&gt;</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">&lt;pcl/io/pcd_io.h&gt;</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">&lt;pcl/point_types.h&gt;</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">&lt;pcl/filters/voxel_grid.h&gt;</span><span class="cp"></span>
<span class="kt">int</span>
<span class="nf">main</span> <span class="p">()</span>
<span class="p">{</span>
<span class="n">pcl</span><span class="o">::</span><span class="n">PCLPointCloud2</span><span class="o">::</span><span class="n">Ptr</span> <span class="n">cloud</span> <span class="p">(</span><span class="k">new</span> <span class="n">pcl</span><span class="o">::</span><span class="n">PCLPointCloud2</span> <span class="p">());</span>
<span class="n">pcl</span><span class="o">::</span><span class="n">PCLPointCloud2</span><span class="o">::</span><span class="n">Ptr</span> <span class="n">cloud_filtered</span> <span class="p">(</span><span class="k">new</span> <span class="n">pcl</span><span class="o">::</span><span class="n">PCLPointCloud2</span> <span class="p">());</span>
<span class="c1">// Fill in the cloud data</span>
<span class="n">pcl</span><span class="o">::</span><span class="n">PCDReader</span> <span class="n">reader</span><span class="p">;</span>
<span class="c1">// Replace the path below with the path where you saved your file</span>
<span class="n">reader</span><span class="p">.</span><span class="n">read</span> <span class="p">(</span><span class="s">&quot;table_scene_lms400.pcd&quot;</span><span class="p">,</span> <span class="o">*</span><span class="n">cloud</span><span class="p">);</span> <span class="c1">// Remember to download the file first!</span>
<span class="n">std</span><span class="o">::</span><span class="n">cerr</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;PointCloud before filtering: &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">cloud</span><span class="o">-&gt;</span><span class="n">width</span> <span class="o">*</span> <span class="n">cloud</span><span class="o">-&gt;</span><span class="n">height</span>
<span class="o">&lt;&lt;</span> <span class="s">&quot; data points (&quot;</span> <span class="o">&lt;&lt;</span> <span class="n">pcl</span><span class="o">::</span><span class="n">getFieldsList</span> <span class="p">(</span><span class="o">*</span><span class="n">cloud</span><span class="p">)</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;).&quot;</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
<span class="c1">// Create the filtering object</span>
<span class="n">pcl</span><span class="o">::</span><span class="n">VoxelGrid</span><span class="o">&lt;</span><span class="n">pcl</span><span class="o">::</span><span class="n">PCLPointCloud2</span><span class="o">&gt;</span> <span class="n">sor</span><span class="p">;</span>
<span class="n">sor</span><span class="p">.</span><span class="n">setInputCloud</span> <span class="p">(</span><span class="n">cloud</span><span class="p">);</span>
<span class="n">sor</span><span class="p">.</span><span class="n">setLeafSize</span> <span class="p">(</span><span class="mf">0.01f</span><span class="p">,</span> <span class="mf">0.01f</span><span class="p">,</span> <span class="mf">0.01f</span><span class="p">);</span>
<span class="n">sor</span><span class="p">.</span><span class="n">filter</span> <span class="p">(</span><span class="o">*</span><span class="n">cloud_filtered</span><span class="p">);</span>
<span class="n">std</span><span class="o">::</span><span class="n">cerr</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;PointCloud after filtering: &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">cloud_filtered</span><span class="o">-&gt;</span><span class="n">width</span> <span class="o">*</span> <span class="n">cloud_filtered</span><span class="o">-&gt;</span><span class="n">height</span>
<span class="o">&lt;&lt;</span> <span class="s">&quot; data points (&quot;</span> <span class="o">&lt;&lt;</span> <span class="n">pcl</span><span class="o">::</span><span class="n">getFieldsList</span> <span class="p">(</span><span class="o">*</span><span class="n">cloud_filtered</span><span class="p">)</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;).&quot;</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
<span class="n">pcl</span><span class="o">::</span><span class="n">PCDWriter</span> <span class="n">writer</span><span class="p">;</span>
<span class="n">writer</span><span class="p">.</span><span class="n">write</span> <span class="p">(</span><span class="s">&quot;table_scene_lms400_downsampled.pcd&quot;</span><span class="p">,</span> <span class="o">*</span><span class="n">cloud_filtered</span><span class="p">,</span>
<span class="n">Eigen</span><span class="o">::</span><span class="n">Vector4f</span><span class="o">::</span><span class="n">Zero</span> <span class="p">(),</span> <span class="n">Eigen</span><span class="o">::</span><span class="n">Quaternionf</span><span class="o">::</span><span class="n">Identity</span> <span class="p">(),</span> <span class="nb">false</span><span class="p">);</span>
<span class="k">return</span> <span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</td></tr></table></div>
</div>
<div class="section" id="the-explanation">
<h1>The explanation</h1>
<p>Now, let’s break down the code piece by piece.</p>
<p>The following lines of code will read the point cloud data from disk.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span> <span class="c1">// Fill in the cloud data</span>
<span class="n">pcl</span><span class="o">::</span><span class="n">PCDReader</span> <span class="n">reader</span><span class="p">;</span>
<span class="c1">// Replace the path below with the path where you saved your file</span>
<span class="n">reader</span><span class="p">.</span><span class="n">read</span> <span class="p">(</span><span class="s">&quot;table_scene_lms400.pcd&quot;</span><span class="p">,</span> <span class="o">*</span><span class="n">cloud</span><span class="p">);</span> <span class="c1">// Remember to download the file first!</span>
</pre></div>
</div>
<p>Then, a <em>pcl::VoxelGrid</em> filter is created with a leaf size of 1cm, the input
data is passed, and the output is computed and stored in <em>cloud_filtered</em>.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span> <span class="n">pcl</span><span class="o">::</span><span class="n">VoxelGrid</span><span class="o">&lt;</span><span class="n">pcl</span><span class="o">::</span><span class="n">PCLPointCloud2</span><span class="o">&gt;</span> <span class="n">sor</span><span class="p">;</span>
<span class="n">sor</span><span class="p">.</span><span class="n">setInputCloud</span> <span class="p">(</span><span class="n">cloud</span><span class="p">);</span>
<span class="n">sor</span><span class="p">.</span><span class="n">setLeafSize</span> <span class="p">(</span><span class="mf">0.01f</span><span class="p">,</span> <span class="mf">0.01f</span><span class="p">,</span> <span class="mf">0.01f</span><span class="p">);</span>
<span class="n">sor</span><span class="p">.</span><span class="n">filter</span> <span class="p">(</span><span class="o">*</span><span class="n">cloud_filtered</span><span class="p">);</span>
</pre></div>
</div>
<p>Finally, the data is written to disk for later inspection.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span> <span class="n">pcl</span><span class="o">::</span><span class="n">PCDWriter</span> <span class="n">writer</span><span class="p">;</span>
<span class="n">writer</span><span class="p">.</span><span class="n">write</span> <span class="p">(</span><span class="s">&quot;table_scene_lms400_downsampled.pcd&quot;</span><span class="p">,</span> <span class="o">*</span><span class="n">cloud_filtered</span><span class="p">,</span>
<span class="n">Eigen</span><span class="o">::</span><span class="n">Vector4f</span><span class="o">::</span><span class="n">Zero</span> <span class="p">(),</span> <span class="n">Eigen</span><span class="o">::</span><span class="n">Quaternionf</span><span class="o">::</span><span class="n">Identity</span> <span class="p">(),</span> <span class="nb">false</span><span class="p">);</span>
</pre></div>
</div>
</div>
<div class="section" id="compiling-and-running-the-program">
<h1>Compiling and running the program</h1>
<p>Add the following lines to your CMakeLists.txt file:</p>
<div class="highlight-cmake notranslate"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre> 1
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12</pre></div></td><td class="code"><div class="highlight"><pre><span></span><span class="nb">cmake_minimum_required</span><span class="p">(</span><span class="s">VERSION</span> <span class="s">3.5</span> <span class="s">FATAL_ERROR</span><span class="p">)</span>
<span class="nb">project</span><span class="p">(</span><span class="s">voxel_grid</span><span class="p">)</span>
<span class="nb">find_package</span><span class="p">(</span><span class="s">PCL</span> <span class="s">1.2</span> <span class="s">REQUIRED</span><span class="p">)</span>
<span class="nb">include_directories</span><span class="p">(</span><span class="o">${</span><span class="nv">PCL_INCLUDE_DIRS</span><span class="o">}</span><span class="p">)</span>
<span class="nb">link_directories</span><span class="p">(</span><span class="o">${</span><span class="nv">PCL_LIBRARY_DIRS</span><span class="o">}</span><span class="p">)</span>
<span class="nb">add_definitions</span><span class="p">(</span><span class="o">${</span><span class="nv">PCL_DEFINITIONS</span><span class="o">}</span><span class="p">)</span>
<span class="nb">add_executable</span> <span class="p">(</span><span class="s">voxel_grid</span> <span class="s">voxel_grid.cpp</span><span class="p">)</span>
<span class="nb">target_link_libraries</span> <span class="p">(</span><span class="s">voxel_grid</span> <span class="o">${</span><span class="nv">PCL_LIBRARIES</span><span class="o">}</span><span class="p">)</span>
</pre></div>
</td></tr></table></div>
<p>After you have made the executable, you can run it. Simply do:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ ./voxel_grid
</pre></div>
</div>
<p>You will see something similar to:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">PointCloud</span> <span class="n">before</span> <span class="n">filtering</span><span class="p">:</span> <span class="mi">460400</span> <span class="n">data</span> <span class="n">points</span> <span class="p">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="n">intensity</span> <span class="n">distance</span> <span class="n">sid</span><span class="p">)</span><span class="o">.</span>
<span class="n">PointCloud</span> <span class="n">after</span> <span class="n">filtering</span><span class="p">:</span> <span class="mi">41049</span> <span class="n">data</span> <span class="n">points</span> <span class="p">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="n">intensity</span> <span class="n">distance</span> <span class="n">sid</span><span class="p">)</span><span class="o">.</span>
</pre></div>
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