Check When a Point is Inside a Mesh
How To Check When Point is Inside a Mesh
This mesh method takes a Vector3 point and checks if it inside the mesh.
Design Outline
- Check if point inside or outside of bounding box, when inside continue with following checks;
- Cast a ray from the point in the positive and negative x directions;
- When there is a hit, move forward from hit point a very small amount along ray direction and recast ray from new point;
- Count hits, when zero or an odd number of hits then point is inside mesh and for a even number of hits > 0 non zero then point is outside of mesh.
Design Method
- Check bounding box;
var boundInfo = this.getBoundingInfo();var max = boundInfo.maximum;var min = boundInfo.minimum;if(point.x < min.x || point.x > max.x) { return false;}if(point.y < min.y || point.y > max.y) { return false;}if(point.z < min.z || point.z > max.z) { return false;}
- Use the diameter of the mesh's bounding sphere as the distance to cast the ray
var diameter = 2 * boundInfo.boundingSphere.radius;ray = new BABYLON.Ray(point, direction, diameter);
- Set hit count to zero, while hits occurring increment hit count
var hitCount = 0;var pickInfo = ray.intersectsMesh(this);while (pickInfo.hit) { hitCount++; pickInfo.pickedPoint.addToRef(direction.scale(0.00000001), point); //move point a small amout in ray direction ray.origin = point; pickInfo = ray.intersectsMesh(this);}
- Count hits.
if((hitCount % 2) === 1) { var pointFound = true;}else if ((hitCount % 2) === 0 && hitCount > 0) { var pointFound = true;}
return pointFound;
The Whole Function
Returns true if point is inside mesh, false otherwise.
BABYLON.Mesh.prototype.pointIsInside = function (point) { var boundInfo = this.getBoundingInfo(); var max = boundInfo.maximum; var min = boundInfo.minimum; var diameter = 2 * boundInfo.boundingSphere.radius; if(point.x < min.x || point.x > max.x) { return false; } if(point.y < min.y || point.y > max.y) { return false; } if(point.z < min.z || point.z > max.z) { return false; }
var pointFound = false; var d = 0; var hitCount = 0; var gap = 0; var distance = 0; var ray = new BABYLON.Ray(BABYLON.Vector3.Zero(), BABYLON.Axis.X, diameter);; var pickInfo; var direction = point.clone(); var refPoint = point.clone();
hitCount = 0; ray.origin = refPoint; ray.direction = direction; ray.distance = diameter; pickInfo = ray.intersectsMesh(this); while (pickInfo.hit) { hitCount++; pickInfo.pickedPoint.addToRef(direction.scale(0.00000001), refPoint); ray.origin = refPoint; pickInfo = ray.intersectsMesh(this); } if((hitCount % 2) === 1) { pointFound = true; } return pointFound;};
Playground Example
Generate random points in a volume around a twelve pointed star mesh. Place a sphere at each point and turn it red when inside the star.
Twelve Pointed StarFurther reading
Create Points Inside A Mesh
Helpful code snippet for creating points inside of a mesh in Babylon.js.

Draw Points on a Mesh Surface
Helpful code snippet for drawing points on a mesh surface in Babylon.js.
