How to move the camera to center an object in screen?

Question

For example, an object is located at (x,y,z) in world space. Now how to calculate the offset translation, I mean no rotation, that will be applied to the camera so as to place the object at the center of the screen?

BTW, I'm using three.js r91. But pseudo code/C++/C# is also OK.

Answer 1

If you want to move the camera a certain distance from an object, and looking at the object, while preserving the camera's rotation, just move the camera at the object's location, then translate on the +Z axis (or -Z, depending where your camera is looking at).

camera.position = object.position;
camera.Translate(0, 0, -r); // where `r` is the desired distance

Answer 2

You need to position the camera relative to the object using the negative of its front vector (zAxis) multiplied by the distance you want.

var ignore1 = new Vector3();
var ignore2 = new Vector3();
var front_vector = new Vector3();

// get the direction the camera is pointing at
camera.matrix.extractBasis ( ignore1, ignore2, front_vector );

// put the camera at a negative distance from the object
camera.position.copy(object.position);
camera.position.addScaledVector(front_vector, -distance_from_object);