You could use modelX, Y and Z functions.

Code Example

1. void setup() {
2.   size(500, 500, P3D);
3.   noStroke();
4.   smooth();
5. }
6.  
7. void draw() {
8.   background(0);
9.  
10.   pushMatrix();
11.   translate(width/2, height/2, 0);
12.   translate(200, 100, 0); 
13.   fill(255);
14.   ellipse(0, 0, 50, 50);
15.   float x = modelX(0, 0, 0);
16.   float y = modelY(0, 0, 0);
17.   popMatrix();
18.  
19.   fill(255, 0, 0);
20.   ellipse(x, y, 25, 25);
21. }