7

I'm having hard times figuring out what's the best way to check if a Object3d is visible for the eyes of the camera.

I'm having a sphere in the middle of the screen. Some cubes are added on it's surface randomly. What I would need is a way to check which cubes are visible (on the front half of the sphere) and which one are invisible (on the back half of the sphere) for the eyes of the camera.

What I have found so far seems to be the right direction - but I must be missing something with the THREE.Raytracer class.

Here is a fiddle of the code that I'm using: jsfiddle. I have tried to make it as clear as possible.

This part of the fiddle might contain the buggy code:

var raycaster = new THREE.Raycaster();
var origin = camera.position, direction, intersects, rayGeometry = new THREE.Geometry(), g;
pointGroup.children.forEach(function(pointMesh) {
    direction = pointMesh.position.clone();
    // I THINK THIS CALCULATION MIGHT BE WRONG - BUT DON'T KNOW HOW TO CORRECT IT
    raycaster.set(origin, direction.sub(origin).normalize());
    // if the pointMesh's position is on the back half of the globe, the ray should intersect with globe first and the hit the point as second target - because the cube is hidden behind the bigger sphere object
    intersects = raycaster.intersectObject(pointMesh);
    // this is always empty - should contain objects that are located on the back of the sphere ...
    console.log(intersects);
});

Frustum Culling is not working as outlined in this stack overflow question here: post1

Also this post2 and this post3 are explaining the topic really good but not quite for this situation.

Thank you for you help!

Community
  • 1
  • 1
hetsch
  • 1,508
  • 2
  • 12
  • 27
  • Any luck on this? We're trying that now, and using raycaster.intersectObjects (plural) to no avail, although it DOES gives us a hit when our camera physically runs into the blocking object. Raycaster.intersectObject (singular) always gives us nothing. – Alien Life Form Jul 28 '14 at 20:16
  • What worked for me in an other situation was using the recursive parameter of intersectObjects(toTest, true). I have totally overlooked that parameter. – hetsch Jul 30 '14 at 07:34
  • see https://stackoverflow.com/questions/29758233/three-js-check-if-object-is-still-in-view-of-the-camera – Martin Jan 23 '19 at 14:41

2 Answers2

4

You want to look at Occlusion Culling techniques. Frustum culling works fine and is not what you are describing. Frustum culling just checks if an object (or its bounding box) is inside the camera pyramid. You perform Occlusion culling in addition to Frustum Culling specially when you want to eliminate objects which are occluded by other objects inside the view frustum. But it is not an easy task.

gaitat
  • 12,449
  • 4
  • 52
  • 76
  • Thank you for the valuable information information. Till now i have never heard about occlusion culling, but it seems to be one way to go. Have to dig into. Just wait if someone comes up with another solution. – hetsch Mar 12 '14 at 12:25
1

I just worked though a similar problem where I was trying to detect when a point in world space passed out of view of the camera and behind specific objects in the scene. I created a jsfiddle, (see below) for it. When the red "target" passes behind any of the three "walls" a blue line is drawn from the "target" to the camera. I hope this helps.

user3889022
  • 75
  • 2
  • 7