Merge pull request #359 from jpahm/documentation

Create static_occupancy_node.md

docs/Perception/static_occupancy_node.md

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+---
+layout: default
+title: Node Template
+nav_order: 2
+parent: Perception
+---
+
+# static_occupancy_node
+{: .no_toc }
+
+*Maintained by Nova*
+
+## Overview
+The `StaticOccupancyNode` is a ROS 2 node responsible for generating static occupancy and mass grids based on ground-segmented pointclouds provided by the 
+[`ground_segmentation_node`](https://github.com/jpahm/navigator/blob/documentation/docs/Perception/ground_segmentation_node.md). 
+These grids are then consumed by the 
+[`junction_manager`](https://github.com/jpahm/navigator/blob/documentation/docs/Planning/junction_manager.md) 
+and the 
+[`grid_summation_node`](https://github.com/jpahm/navigator/blob/documentation/docs/Planning/grid_summation_node.md) 
+for planning purposes.
+
+The **occupancy grid** is generated using 
+[Dempster-Shafer Thoery (DST)](https://en.wikipedia.org/wiki/Dempster%E2%80%93Shafer_theory) 
+with a process which roughly consists of three steps:
+- Ray-tracing free space toward occupied space
+- Filling the remaining grid with free space, also using ray-tracing
+- Adding an occupied space representing the vehicle
+
+The **mass grid** is generated via the following steps:
+- Updating the previous mass grid via a decay factor
+- Updating probabilities of this decayed grid using a [Bayes filter](https://en.wikipedia.org/wiki/Recursive_Bayesian_estimation)
+
+These grids are then published separately, with the occupancy grid data being populated by the averaged
+occupied and free probability values obtained via generation of the mass grid.
+
+---
+
+### In:
+- **clock_sub** [*Clock*](https://docs.ros2.org/galactic/api/rosgraph_msgs/msg/Clock.html)
+- **pcd_sub** [*PointCloud2*](https://docs.ros2.org/galactic/api/sensor_msgs/msg/PointCloud2.html)
+
+### Out:
+- **occupancy_grid_pub** [*OccupancyGrid*](https://docs.ros2.org/galactic/api/nav_msgs/msg/OccupancyGrid.html)
+- **masses_pub** [*Masses*](https://github.com/Nova-UTD/navigator/blob/documentation/src/msg/navigator_msgs/msg/Masses.msg)
+
+---
+
+### Individual Function 1
+blabla bla bla blabla blablabla blabla bla bla blabla blablablablabla bla bla blabla blablabla
+blabla bla bla blabla blablabla blabla bla bla blabla blablabla
+
+### Individual Function 2
+blabla bla bla blabla blablabla blabla bla bla blabla blablablablabla bla bla blabla blablabla
+blabla bla bla blabla blablabla blabla bla bla blabla blablabla