title: SurfacePlotMesh (FXyz) constructor arguments
body: <p>I would like to know if I am correct with understanding the constructor argument as a <code>Function&lt;Point2D, Number&gt; function</code>. 
  My function which I have used for 1D charts based on the applying the variables after every step on the x axis, but there is as a parametr <code>Point2D</code> which contain 2 variables : <code>x</code> and <code>y</code>, if i am correct the <code>x</code> varriable is step which increase "0.5" for every calculations after <code>apply</code> the function of y. 
  Then what is the second parametr of generic type, the <code>Number</code> ? 
  How could I implement other functions, using the <code>SurfacePlotMesh</code> class. Could someone explain me a little bit how it works ? Or link the documenations ( If it exist ) ? </p>