Get Random Position on NavMesh in Unity

NavMeshUtil.cs

using UnityEngine.AI;
using UnityEngine;

public static class NavMeshUtil {
    
    // Get Random Point on a Navmesh surface
    public static Vector3 GetRandomPoint(Vector3 center, float maxDistance) {
        // Get Random Point inside Sphere which position is center, radius is maxDistance
        Vector3 randomPos = Random.insideUnitSphere * maxDistance + center;

        NavMeshHit hit; // NavMesh Sampling Info Container

        // from randomPos find a nearest point on NavMesh surface in range of maxDistance
        NavMesh.SamplePosition(randomPos, out hit, maxDistance, NavMesh.AllAreas);

        return hit.position;
    }
}

Vector3 returning (infinity,infinity,infinity)

Considering this is the second result when googling around, I will leave my experiences here.

There are a few problems here.

• The NavMesh#SamplePosition returns a boolean. True if it found a point, false if not. This is not being checked. If the sampling fails, the code will break. Using the return value of SamplePosition in an if statement will remove the errors from that.
• Navmesh#SamplePosition gets any position on the navmesh. If there are two disconnect areas and the sample distance is far enough, it will find a position on the navmesh which your agent might not be able to get to. See the image (sampling from camera position).
  

To get around the second problem, I would calculate the path before setting the destination to make sure it is reachable.
I have not tested this, but I'm sure you can figure something out along these lines.

bool foundPosition = NavMesh.SamplePosition(
    origin + Random.insideUnitSphere * maxRange,
    out navMeshHit,
    maxRange,
    NavMesh.AllAreas
);

if (!foundPosition)
    // throw exception, return false, retry, some other way to handle failed sample

NavMeshPath path = new NavMeshPath();
this.navmeshAgent.CalculatePath(navMeshHit.position, path);
canReachPoint = path.status == NavMeshPathStatus.PathComplete;

Considering this is the second result when googling around, I will leave my experiences here.

There are a few problems here.

• The NavMesh#SamplePosition returns a boolean. True if it found a point, false if not. This is not being checked. If the sampling fails, the code will break. Using the return value of SamplePosition in an if statement will remove the errors from that.
• Navmesh#SamplePosition gets any position on the navmesh. If there are two disconnect areas and the sample distance is far enough, it will find a position on the navmesh which your agent might not be able to get to. See the image (sampling from camera position).
  

To get around the second problem, I would calculate the path before setting the destination to make sure it is reachable. I have not tested this, but I'm sure you can figure something out along these lines.

bool foundPosition = NavMesh.SamplePosition(
    origin + Random.insideUnitSphere * maxRange,
    out navMeshHit,
    maxRange,
    NavMesh.AllAreas
);

if (!foundPosition)
    // throw exception, return false, retry, some other way to handle failed sample

NavMeshPath path = new NavMeshPath();
this.navmeshAgent.CalculatePath(navMeshHit.position, path);
canReachPoint = path.status == NavMeshPathStatus.PathComplete;

thanks! :D I will update codes

If you don't mind having the "random" points in a grid, you can pregenerate points according to the navmesh's bounds and generate points using Mathf.PerlinNoise

Afterwards you can exclude all points that aren't found by NavMesh.SamplePosition and then choose a random valid point with Random.Range(0, pointList.Count)