Is it possible to track an animated object within Geometry Nodes with a camera?

Question

Is there a chance to track an object/instance generated inside Geometry Nodes with a camera? Can I provide the coordinates of an animated Object per attribute to an Object Constraint?

This is a small animation made with Geometry Nodes. I want to track one of these objects with a camera. Is this possible?

Answer 1

Since you're re-creating and animating your cube inside your Geometry Nodes and the original is stationary, the Track To constraint on your Camera is not doing anything. On that constraint modifier, there's an option to follow a vertex group as well, maybe we could create a vertex selection out of the animated cubes inside GN and tell the modifier to follow that? Unfortunately, that's not possible unless you apply your GN modifier and destroy its procedurality in the process, since GN cannot create vertex groups, not exactly (for a more detailed explanation as to why not, you can take a look at this answer).

Still, there's a possible workaround for that vertex group idea:

• Create a new object, a plane for example. Let's name it TARGET. We need only a single vertex, so enter into Edit Mode, select everything, M (Merge) > At Center.
• That single vertex still selected, create a vertex group out of it (Ctrl+G). Let's name it FOLLOW.
• In your main Geometry Nodes setup where all the animation is happening, turn the cube you want to follow into an instance, either by ticking the As Instance option on the Object Info node, or by using a Geometry to Instance. Then, using a Store Named Attribute node, capture its Position. I named the attribute LOOKAT.
• Add a Geometry Nodes modifier to your TARGET object. Get the position information we captured in the main setup into this one via a Sample Index node, and use that to Set Position of our single vertex.
• Finally, on your Track To constraint of your camera, choose TARGET and FOLLOW as the object and vertex group, respectively.

In summary, your main GN setup will continuously capture your cube's position and write it down as an attribute named LOOKAT. Then your TARGET object's GN setup will take that and use it to move its single vertex to that position. Since we're not creating new geometry in that setup, our vertex group will not be lost, and can be used in our camera's tracking constraint.

Since these movements are all happening in the local space, you might wanna parent your TARGET object to your main GN object in case you'd want to move or rotate them.

Update, answering OP's question in the comments as to how to set this up for an object generated inside the main GN modifier:

• When you turn a geometry into an instance, the "origin" of the instance will always be created at $[0,0,0]$, so if you do that after moving it with Set Position, its origin will stay there while the mesh moves around. Since the Camera is following the position of the instance, not its mesh, it won't move either. Simply putting Geometry to Instance right after the Icosphere node will prevent this:

• The other important part here is the Sample Index/Transfer Attribute node. When you use Join Geometry, the merging objects will get their indices according to the order of their noodles from top to bottom. In your case there are three objects going in: Bezier curve, Icosphere, and Cube. Bezier curve is not an instance, so it doesn't get an instance index. In your setup you happened to link the Icosphere below the Cube, so it gets the second index, $1$. Which means you need to tell that to the Sample Index/Transfer Attribute node in your target GN setup:

Answer 2

We want to track, what, the median point of some instanced geometry?I would use a different technique than those so far offered. Let's use another GN object to acquire that median point, shrinkwrap constrain an empty to that GN object, and then track that empty.

GNCube makes a cube using GN; this is our example of geometry that we want to track. InstanceGN then instances that same object, then just moves all of its vertices to their median point. An empty then acquires that median point by shrinkwrapping to the nearest vertex of InstanceGN (where all vertices are at the exact same location, so it doesn't matter which one gets used), and the camera tracks that empty.

It's not technically necessary to realize instances. We could use three transform nodes to scale the instance to 0 at this median point instead. We can of course offset that position (in any particular space we'd like, the only thing transforming InstanceGN will do is to change its space.) If we'd like, we could even specify an attribute input to InstanceGN's modifier to allows us to specify a selection for our median. InstanceGN will read the attribute specified from GNCube:

Here, GN cube is outputting an "att" of 1 for its last two verts and 0 for its other verts, so we're only tracking the median of those two verts instead.

Answer 3

I hope I am not over my head, there is another walk around to realize this track in just one geometry nodes but it's a more complex and it have limitations. The idea is to have groups of vertex within just one vertex. Those vertex will be animated then support the objects as instances.

It work but you can't realize the instances it will break. That being said it's work exactly on the same principles of the Kuboå solution.