code: function(theta_p,theta){
          if(arguments.length > 1){
              this.theta = theta;
              this.rootPos = new Vec2D(theta_p);
          } else {
              this.rootPos = new Vec2D();
              this.theta = theta_p;
          }
          //due to lack-of int/float types, no support of theta in degrees
      }
docs: either Vec2D + angle 
  @param {Vec2D | Number} vector | angle
  @param {Number} [theta]