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<span class="md-ellipsis">
Global callback slot
</span>
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<a href="#extension-module" class="md-nav__link">
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Extension module
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<div class="md-content" data-md-component="content">
<article class="md-content__inner md-typeset">
<h1 id="extending-glim">Extending GLIM</h1>
<h2 id="notation">Notation</h2>
<p>In this package, the (SE3) transformation from frame B to frame A is denoted as <code>T_A_B</code>. In other words, a point <code>p_B</code> in the frame B is transformed into the frame A by <code>T_A_B</code> (i.e., <code>p_A = T_A_B * p_B</code>).</p>
<p>For instance, the transformation from a LiDAR frame to the world frame (i.e., a LiDAR pose in the world frame) is represented as <code>T_world_lidar</code>, and a point in the LiDAR frame <code>p_lidar</code> is transformed into the world frame by <code>p_world = T_world_lidar * p_lidar</code>.</p>
<p>Similarty, <code>v_A_B</code> represents the velocity of frame B in frame A, and thus <code>v_world_imu</code> represents an IMU velocity in the world frame.</p>
<h2 id="variables">Variables</h2>
<h3 id="variable-addressing-in-gtsam">Variable addressing in GTSAM</h3>
<p>In GTSAM, variables can be addressed using the <strong><em>gtsam::Symbol</em></strong> class that combines a symbol label (a character, e.g., 'x') and a variable index. For example, you can insert a pose variable into <strong><em>gtsam::Values</em></strong> and label it as <code>X(i)</code> as follows:</p>
<div class="highlight"><pre><span></span><code><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="k">using</span><span class="w"> </span><span class="n">gtsam</span><span class="o">::</span><span class="n">symbol_shorthand</span><span class="o">::</span><span class="n">X</span><span class="p">;</span>
<a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a>
<a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a><span class="kt">int</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a><span class="n">gtsam</span><span class="o">::</span><span class="n">Pose3</span><span class="w"> </span><span class="n">pose</span><span class="p">;</span>
<a id="__codelineno-0-5" name="__codelineno-0-5" href="#__codelineno-0-5"></a>
<a id="__codelineno-0-6" name="__codelineno-0-6" href="#__codelineno-0-6"></a><span class="n">gtsam</span><span class="o">::</span><span class="n">Values</span><span class="w"> </span><span class="n">values</span><span class="p">;</span>
<a id="__codelineno-0-7" name="__codelineno-0-7" href="#__codelineno-0-7"></a><span class="n">values</span><span class="p">.</span><span class="n">insert</span><span class="p">(</span><span class="n">X</span><span class="p">(</span><span class="n">id</span><span class="p">),</span><span class="w"> </span><span class="n">pose</span><span class="p">);</span>
</code></pre></div>
<div class="admonition info">
<p class="admonition-title">Info</p>
<p>See <strong>5.2. Keys and Symbols</strong> in <a href="https://gtsam.org/tutorials/intro.html">this tutorial</a> for more details.</p>
</div>
<h3 id="variables-in-glim">Variables in GLIM</h3>
<p>In the following, we show the graph structures and variables in the odometry estimation and global optimization algorithms of GLIM. Through the global callback slot mechanism, which will be explained later, you can access variables in the factor graphs and create additional constraints (i.e., factors) to improve the accuracy/stability/robustness of the mapping process in specific situations.</p>
<h4 id="variables-in-the-odometry-estimation">Variables in the odometry estimation</h4>
<ul>
<li><code>X(i)</code> : IMU pose = T_odom_imu (gtsam::Pose3)</li>
<li><code>V(i)</code> : IMU velocity = v_odom_imu (gtsam::Vector3)</li>
<li><code>B(i)</code> : IMU bias (gtsam::imuBias::ConstantBias)</li>
</ul>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>In the odometry estimation, old variables are eliminated from the graph when they leave the sliding optimization window specified by the <strong>smoother_lag</strong> param (e.g., 5 sec). You thus need to ensure that additional factors refer to only variables in this optimization window. </p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Because <strong>odometry_ct</strong> performs LiDAR-only estimation, it does not create <code>V(i)</code> and <code>B(i)</code>, and <code>X(i)</code> represents the LiDAR pose instead of the IMU pose.</p>
</div>
<div class="admonition info">
<p class="admonition-title">Info</p>
<p><a href="https://github.com/koide3/glim_ext/blob/master/modules/odometry/velocity_suppressor/src/glim_ext/velocity_suppressor.cpp">"velocity_suppressor.cpp"</a> in <strong>gtsam_points</strong> shows a simple example to insert velocity suppression factors into the odometry estimation factor graph.</p>
</div>
<h4 id="variables-in-the-global-optimization">Variables in the global optimization</h4>
<p><strong>Sub mapping states</strong>:</p>
<ul>
<li><code>X(i)</code> : Sensor pose = T_odom_sensor (gtsam::Pose3)</li>
<li><code>V(i)</code> : IMU velocity = v_odom_sensor (gtsam::Vector3)</li>
<li><code>B(i)</code> : IMU bias (gtsam::imuBias::ConstantBias)</li>
</ul>
<p><strong>Global mapping states</strong>:</p>
<ul>
<li><code>X(i)</code> : Submap pose = T_world_submap (gtsam::Pose3)</li>
<li><code>V(2 * i) & V(2 * i + 1)</code> : IMU velocity at endpoints (gtsam::Vector3)</li>
<li><code>B(2 * i) & V(2 * i + 1)</code> : IMU bias at endpoints (gtsam::Vector3)</li>
</ul>
<h2 id="global-callback-slot">Global callback slot</h2>
<p>The global callback slot is a mechanism to hook processing steps in the mapping system. It enables to access the internal states of the mapping process and insert additional factors into the factor graph. The following code demonstrates how we can register a callback function to the new frame creation event in the odometry estimation and retrieve estimated sensor states of the latest frame.</p>
<div class="highlight"><pre><span></span><code><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="cp">#include</span><span class="w"> </span><span class="cpf"><glim/odometry/callback.hpp></span>
<a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a>
<a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="k">using</span><span class="w"> </span><span class="k">namespace</span><span class="w"> </span><span class="nn">glim</span><span class="p">;</span>
<a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a>
<a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="kt">void</span><span class="w"> </span><span class="nf">on_new_frame</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">EstimationFrame</span><span class="o">::</span><span class="n">ConstPtr</span><span class="o">&</span><span class="w"> </span><span class="n">new_frame</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">long</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">new_frame</span><span class="o">-></span><span class="n">id</span><span class="p">;</span><span class="w"> </span><span class="c1">// Frame ID</span>
<a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">stamp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">new_frame</span><span class="o">-></span><span class="n">stamp</span><span class="p">;</span><span class="w"> </span><span class="c1">// Timestamp</span>
<a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Eigen</span><span class="o">::</span><span class="n">Isometry3d</span><span class="o">&</span><span class="w"> </span><span class="n">T_world_imu</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">new_frame</span><span class="o">-></span><span class="n">T_world_imu</span><span class="p">;</span><span class="w"> </span><span class="c1">// IMU pose</span>
<a id="__codelineno-1-9" name="__codelineno-1-9" href="#__codelineno-1-9"></a><span class="p">}</span>
<a id="__codelineno-1-10" name="__codelineno-1-10" href="#__codelineno-1-10"></a>
<a id="__codelineno-1-11" name="__codelineno-1-11" href="#__codelineno-1-11"></a><span class="kt">void</span><span class="w"> </span><span class="nf">setup_callback</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-1-12" name="__codelineno-1-12" href="#__codelineno-1-12"></a><span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">placeholders</span><span class="o">::</span><span class="n">_1</span><span class="p">;</span>
<a id="__codelineno-1-13" name="__codelineno-1-13" href="#__codelineno-1-13"></a><span class="w"> </span><span class="n">OdometryEstimationCallback</span><span class="o">::</span><span class="n">on_new_frame</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">bind</span><span class="p">(</span><span class="o">&</span><span class="n">on_new_frame</span><span class="p">,</span><span class="w"> </span><span class="n">_1</span><span class="p">));</span>
<a id="__codelineno-1-14" name="__codelineno-1-14" href="#__codelineno-1-14"></a><span class="p">}</span>
</code></pre></div>
<p>Take a look at the following links to see what can be retrieved from and inserted into the system via global callback slots:</p>
<ul>
<li><a href="glim/structglim_1_1OdometryEstimationCallbacks.html">OdometryEstimationCallbacks</a></li>
<li><a href="glim/structglim_1_1SubMappingCallbacks.html">SubMappingCallbacks</a></li>
<li><a href="glim/structglim_1_1GlobalMappingCallbacks.html">GlobalMappingCallbacks</a></li>
</ul>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Each of odometry estimation, submapping, and global mapping modules are run in different threads, and thus their callbacks can be called from different threads. <strong>You must take care of the thread-safety</strong> of your extension module if it subscribes to events from different modules.</p>
</div>
<h2 id="extension-module">Extension module</h2>
<p>GLIM offers a mechanism to load extension modules from shared libraries at run-time. To implement an extension module, you need to write your extension module class that inherits from <strong><em>glim::ExtensionModule</em></strong> and define a loading function named <strong><em>create_extension_module()</em></strong> that returns an instance of your extension class.</p>
<div class="highlight"><span class="filename">my_extension_module.cpp</span><pre><span></span><code><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="cp">#include</span><span class="w"> </span><span class="cpf"><glim/odometry/callbacks.hpp></span>
<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="cp">#include</span><span class="w"> </span><span class="cpf"><glim/util/extension_module.hpp></span>
<a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a>
<a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a><span class="k">using</span><span class="w"> </span><span class="k">namespace</span><span class="w"> </span><span class="nn">glim</span><span class="p">;</span>
<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a>
<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a><span class="k">class</span><span class="w"> </span><span class="nc">MyExtensionModule</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="k">public</span><span class="w"> </span><span class="n">ExtensionModule</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a><span class="k">public</span><span class="o">:</span>
<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a><span class="w"> </span><span class="n">MyExtensionModule</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="w"> </span><span class="k">using</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">placeholders</span><span class="o">::</span><span class="n">_1</span><span class="p">;</span>
<a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a><span class="w"> </span><span class="n">OdometryEstimationCallbacks</span><span class="o">::</span><span class="n">on_new_frame</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">bind</span><span class="p">(</span><span class="o">&</span><span class="n">MyExtensionModule</span><span class="o">::</span><span class="n">on_new_frame</span><span class="p">,</span><span class="w"> </span><span class="k">this</span><span class="p">,</span><span class="w"> </span><span class="n">_1</span><span class="p">));</span>
<a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></a><span class="w"> </span><span class="p">}</span>
<a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a>
<a id="__codelineno-2-13" name="__codelineno-2-13" href="#__codelineno-2-13"></a><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">on_new_frame</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">EstimationFrame</span><span class="o">::</span><span class="n">ConstPtr</span><span class="o">&</span><span class="w"> </span><span class="n">frame</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-2-14" name="__codelineno-2-14" href="#__codelineno-2-14"></a><span class="w"> </span><span class="c1">// ...</span>
<a id="__codelineno-2-15" name="__codelineno-2-15" href="#__codelineno-2-15"></a><span class="w"> </span><span class="p">}</span>
<a id="__codelineno-2-16" name="__codelineno-2-16" href="#__codelineno-2-16"></a><span class="p">};</span>
<a id="__codelineno-2-17" name="__codelineno-2-17" href="#__codelineno-2-17"></a>
<a id="__codelineno-2-18" name="__codelineno-2-18" href="#__codelineno-2-18"></a><span class="k">extern</span><span class="w"> </span><span class="s">"C"</span><span class="w"> </span><span class="n">ExtensionModule</span><span class="o">*</span><span class="w"> </span><span class="n">create_extension_module</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<a id="__codelineno-2-19" name="__codelineno-2-19" href="#__codelineno-2-19"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">MyExtensionModule</span><span class="p">();</span>
<a id="__codelineno-2-20" name="__codelineno-2-20" href="#__codelineno-2-20"></a><span class="p">}</span>
</code></pre></div>
<div class="highlight"><span class="filename">CMakeLists.txt</span><pre><span></span><code><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a><span class="nb">cmake_minimum_required</span><span class="p">(</span><span class="s">VERSION</span><span class="w"> </span><span class="s">3.5.2</span><span class="p">)</span>
<a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a><span class="nb">project</span><span class="p">(</span><span class="s">my_extension_module</span><span class="p">)</span>
<a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a>
<a id="__codelineno-3-4" name="__codelineno-3-4" href="#__codelineno-3-4"></a><span class="nb">set</span><span class="p">(</span><span class="s">CMAKE_CXX_STANDARD</span><span class="w"> </span><span class="s">17</span><span class="p">)</span>
<a id="__codelineno-3-5" name="__codelineno-3-5" href="#__codelineno-3-5"></a>
<a id="__codelineno-3-6" name="__codelineno-3-6" href="#__codelineno-3-6"></a><span class="nb">find_package</span><span class="p">(</span><span class="s">glim</span><span class="w"> </span><span class="s">REQUIRED</span><span class="p">)</span>
<a id="__codelineno-3-7" name="__codelineno-3-7" href="#__codelineno-3-7"></a>
<a id="__codelineno-3-8" name="__codelineno-3-8" href="#__codelineno-3-8"></a><span class="nb">add_library</span><span class="p">(</span><span class="s">my_extension_module</span><span class="w"> </span><span class="s">SHARED</span>
<a id="__codelineno-3-9" name="__codelineno-3-9" href="#__codelineno-3-9"></a><span class="w"> </span><span class="s">src/my_extension_module.cpp</span>
<a id="__codelineno-3-10" name="__codelineno-3-10" href="#__codelineno-3-10"></a><span class="p">)</span>
<a id="__codelineno-3-11" name="__codelineno-3-11" href="#__codelineno-3-11"></a><span class="nb">target_link_libraries</span><span class="p">(</span><span class="s">my_extension_module</span>
<a id="__codelineno-3-12" name="__codelineno-3-12" href="#__codelineno-3-12"></a><span class="w"> </span><span class="s">glim::glim</span>
<a id="__codelineno-3-13" name="__codelineno-3-13" href="#__codelineno-3-13"></a><span class="p">)</span>
</code></pre></div>
<p>The extension module can be loaded into GLIM by adding the name of the created shared library to <code>extension_modules</code> parameter in <code>glim/config/config_ros.json</code>.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If you don't want to use the dynamic loading mechanism, it is also possible to create an extension by directly modifying <code>glim_ros.cpp</code>, of course.</p>
</div>
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