code: public double depth2View( Point2D_F64 a , Point2D_F64 b , Se3_F64 fromAtoB )
  	{
  		DMatrixRMaj R = fromAtoB.getR();
  		Vector3D_F64 T = fromAtoB.getT();
  
  		GeometryMath_F64.multCrossA(b, R, temp0);
  		GeometryMath_F64.mult(temp0,a,temp1);
  
  		GeometryMath_F64.cross(b, T, temp2);
  
  		return -(temp2.x+temp2.y+temp2.z)/(temp1.x+temp1.y+temp1.z);
  	}
docs: Computes pixel depth in image 'a' from two observations.
  
  @param a Observation in first frame.  In calibrated coordinates. Not modified.
  @param b Observation in second frame.  In calibrated coordinates. Not modified.
  @param fromAtoB Transform from frame a to frame b.
  @return Pixel depth in first frame. In same units as T inside of fromAtoB.