March 30, 2020
AI For Beginners
Navigation Meshes
Navigation Meshes
Beginner Programming: Unity Game Dev Courses
Unity Learn Course – AI For Beginners
Navigation Mesh Introduction
Nav Mesh: Unity function for making a navigable area for agents to traverse over.
There are 4 main tabs in the Navigation window:
- Agents
- Area
- Bake
- Object
Agents
Core Parameters: Radius, Height, Step Height, Max Slope
These dimensions determine where the agent can fit when navigating around obstacles, as well as how it can traverse elevation differences. Radius and height help limit where a character can go (cannot go between very small gaps or under objects very close to the ground) where step height is the elevation difference it can traverse in a single jump and max slope is how inclined the surface can be for the agent to travel on. The name allows you to save several types of agents, with various values for these 4 core parameters.
Area
How you define different costs for different types of areas (used in A* pathing).
Bake
Creates the Nav Mesh over your given series of meshes using their polygons. It does this using a template agent called the baked agent size. By default there is only a single mesh created for the default agent type, but there are additional tools that can allow you to create multiple meshes to help handle various sized/types of agents. The Generated Off Mesh Links parameters determine how far off the mesh an agent should be able to jump or drop to get to another mesh location.
Advanced Options (Under Bake):
- Manual Voxel Size: lets you determine the voxel size used to generate the Nav Mesh; larger voxels are less detailed and follow the mesh less accurately; default is 3.00 voxels per agent radius; generally aiming for a value between 2 and 4
- Min Region Area: Helps remove areas that are deemed navigable, but are too small to really be of use or will cause issues by existing
- Height Mesh: bool to determine if Nav Mesh should average elevations to turn steps into slopes or not
Object
Where you can align specific area types to different parts of the mesh, which parts of your mesh you want to generate nav meshes for, and helps create mesh links, which help travel from one nav mesh to another by jumping or falling.
From Waypoints to NavMesh
Introduction of Unity NavMesh, where they introduce the concept of baking the Nav Mesh with use of static game objects and adding the NavMeshAgent component to the AI agents you want to follow the Nav Mesh.
NavMeshAgents
They setup a new scene and project with a Nav Mesh. Nav Mesh specifically looks for “Navigation Static” game objects to build around when baking. They showed that selecting a gameObject before going into play mode with the Nav Mesh active helped visualize how the Nav Mesh was determining their paths.
Areas and Costs
The Areas tab in the Navigation Window lets you set different parts of the mesh as different types of areas. When selecting the polygons or meshes to use for these different areas, select the desired polygons and go to the Object tab. Here you can select which Area to apply to those specific polygons. These areas can then be used to tell agents where they can and cannot go. This is done by going to the NavMeshAgent component of the agent and changing the Area Mask of the Path Finding for that agent. By turning an Area type on or off, you designate which meshes it can travel on at all.
In the Areas tab, you can assign different Cost values to these different areas. This can make them more or less appealing for the agents to traverse across (higher values for cost mean the agents are less likely to use that path).
Following a Player on a NavMesh and Setting Up Off-Mesh Links
This tutorial setup another scene in another project, this time with the basis of following the player around. This was as simple as using the SetDestination method within the NavMeshAgent component to the player’s position in Update.
Off Mesh Links
Off Mesh Links: used if you have gaps in your NavMesh that you want an agent to cross
To create the Mesh Links, select the polygons of interest that you want to link over a gap and go to the Object tab. Here you can select “Generate Mesh Links”. Then go to the Bake tab, set the “Drop Height” and/or “Jump Distance” under the “Generated Off Mesh Links” section, and bake the mesh again to incorporate these links. They will be visually shown as circles between the meshes. Jump Distance is good for crossing horizontal disconnects, where Drop Height is good for crossing significant vertical disconnects. Setting drop links is similar, in that you select the two main groups of meshes in question and generate the mesh links.
Summary
After doing a lot of work with A*, building a path finding system with it from scratch, a lot of the tuning factors and parameters for Nav Mesh made a lot of sense with how A* works. This was good to know there was so much overlap, so I can learn a lot from what they use to work with Nav Mesh to give my A* system effective modifiable parameters to tweak it for designing needs.
Nav Mesh does seem powerful and very easy to get running, but I would have to work with it more to see just how controllable it is. I still like having my own A* system that I know the insides well to tweak exactly how I want it, but the Nav Mesh does offer a lot of similar features I am looking to add so I may need to explore it more to see how easy it is to work with.