ThreeJS Octree Helper Issue

Based on the information provided, you're encountering an "Invalid array length" error when trying to create an OctreeHelper for a larger model with multiple buildings.

This issue is likely related to the size or complexity of your model when all three buildings are included. Here are some potential causes and solutions:

Possible Causes

1. Memory limitations: The Octree may be trying to create too many subdivisions for the larger model
2. Geometry complexity: The combined geometry of all three buildings might be too complex for the default Octree settings
3. Improper collider setup: The collider object might not be properly initialized before creating the OctreeHelper

Suggested Solutions

1. Adjust Octree parameters

Try creating the Octree with custom parameters to limit its depth or subdivision:

JAVASCRIPTCopied
// Create the Octree with custom parameters
const collider = new Octree({
  maxDepth: 8,  // Limit the maximum depth
  maxObjects: 50 // Limit objects per node
});

// Then populate it with your model
collider.fromGraphNode(model);

// Now create the helper
const octree = new OctreeHelper(collider);

2. Create separate Octrees

Instead of one large Octree for all buildings, create individual Octrees for each building:

JAVASCRIPTCopied
// Create separate colliders
const collider1 = new Octree();
const collider2 = new Octree();
const collider3 = new Octree();

// Populate each with a single building
collider1.fromGraphNode(building1);
collider2.fromGraphNode(building2);
collider3.fromGraphNode(building3);

// Create helpers for each
const octreeHelper1 = new OctreeHelper(collider1);
const octreeHelper2 = new OctreeHelper(collider2);
const octreeHelper3 = new OctreeHelper(collider3);

// Add all helpers to the scene
scene.add(octreeHelper1, octreeHelper2, octreeHelper3);

3. Check for model issues

Ensure your model doesn't have any geometry issues:

JAVASCRIPTCopied
// Check if the model has valid geometry before creating the Octree
function validateModel(model) {
  let isValid = true;
  model.traverse(child => {
    if (child.isMesh) {
      const geometry = child.geometry;
      if (!geometry.attributes.position || geometry.attributes.position.count === 0) {
        console.error('Invalid geometry found:', child);
        isValid = false;
      }
    }
  });
  return isValid;
}

// Only create the Octree if the model is valid
if (validateModel(model)) {
  const collider = new Octree();
  collider.fromGraphNode(model);
  const octree = new OctreeHelper(collider);
  scene.add(octree);
}

If these solutions don't resolve the issue, you might need to optimize your model further or consider using a different approach for collision detection with complex models.