Avoiding Obstacles & Define Walk Paths in Crowds Simulation

Download Houdini File: Crowds Intro Avoiding Obstacle.hiplc

Download Houdini File: Crowds Intro Walk Path.hiplc

In this video, I create a wall as an obstacle and tweak the parameters so the Crowd Agents can avoid the wall at all cost in the scene.

I continue from the last video on Avoiding Obstacles and add more complexity to the Crowd simulation by creating a main walk path from a curve node. This main walk path will be the main influence of the direction for the Agents in the Crowd simulation.

Army of Crowd Agents avoiding a Wall

POP Steer Obstacle

Obstacles can be avoided in Houdini’s Crowds tools by using the “POP Steer Obstacle” node. This node acts like a prediction and tries to steer the Crowd Agents away from the obstacle. It’s like driving a car. If you see something in front of you while driving, you’ll start to steer the car away from the obstacle.

Although the POP Steer Obstacle node works well in the Crowd setup, this prediction method isn’t a sure thing. It doesn’t guarantee that all agents will be able to avoid the obstacles. It does require some tweaking with the parameters to get the Crowd simulation to do what you want.

When tweaking with the parameters int he POP Steer node, it’s important to realize this node is a particles node and what is going on behind the scenes with the Crowd Solver. If you read my previous post, “Introduction to Crowds in Houdini” you’ll understand that the Crowd Agents are converted into Houdini’s packed geometry for fast performance. This means that you can treat the Crowd simulation like how you would with a Particle simulation.

External Force Influence

POP Steer nodes are adding additional forces onto the Crowd Agents as if they are particles and thus influencing their direction and force weight. The force weights are important because as you add more additional POP Steer nodes the scene gets more complicated and harder to control. For example, if you want a majority of the Crowd Agents to walk in a specific direction but with variable noise so it looks more natural, force weight will helps. You can assign a larger force weight to the POP Steering node that you wish to be the main direction or bias direction. In a simplistic summary, the majority of the Crowd Agents will head towards the direction with the largest force weight fed into the Crowd Solver.

Using Curves to Influence the Walk Path

Now that we know Crowd Agents can be influenced by POP Steer nodes and the external forces that are generated by these Steer nodes, I want to mention a handy POP Steer Path node. The POP Steer Path node allows you to draw out a curve that is translated into forces that influence your Crowd simulation. The curve that is drawn out, will be the main bias walk path that the Agents will follow.

I thought this node was super cool, because it allows the user a very intuitive way to control the Crowd simulation.