Processing wizards,

I've hit a stumbling block.  My intuition tells me that it is probably a simple calculation, but I'm stuck.

I would like to calculate the angle or radians between two 2d points. I've tried using angleBetween with PVectors and using atan2, but neither seem to be working for me.

What I'd like to be able to do is, given 2 points (one known in advance and one random) be able to place a 3rd point directly behind the random point and be able to draw a straight line through this 3rd point and the the first point that also hits the random point.  Make sense?

Thanks in advance for anyone who might be able to help!

Furly

here's the code i created to try out some various options


PVector origin;
PVector newPoint;
PVector angleP;
void setup(){
 size(800,800);
 origin = new PVector(width/2, height/2);
}

void draw(){
 background(0);
 noFill();
 stroke(255);
 ellipse(width/2,height/2,300,300);
 fill(255);
 ellipse(origin.x,origin.y,5,5);//center point to calculate angle from
 float deg = 220; //try to return this number
 fill(255,0,0);
 newPoint =  drawPoint(deg,150); //new 'random' point
 ellipse(newPoint.x,newPoint.y, 10,10);
 float angle = PVector.angleBetween(newPoint,origin);
 //pushMatrix();
 //translate(width/2, height/2);
 float a = atan2(origin.y - newPoint.y,origin.x - newPoint.x );
//popMatrix();
 println("intial degrees: " + deg + "as radians: " + radians(deg));
 println("angleBetween as radians: " + angle + " as degrees: " + degrees(angle));
 float aRad = radians(a);
 println( "atan2: " + a + " atan2 converted to radians: " + aRad);
 noLoop();
}

PVector drawPoint(float $deg, int $radius){
 float angle = radians($deg);
 float x = width/2 + (cos(angle) * $radius);
 float y = height/2 + (sin(angle) * $radius);
 PVector p;
 p =  new PVector(x,y);
 return p;
}