how to calculate volume of deviation point cloud from integral ?

Hello everyone. I want to find the volume using the formular as in the figure. I constructed the pavement texture point cloud. F(x,y) is the function of point cloud contain x,y,z coordinate so z = F(x,y). It represents the elevation point of pavement texture. F0 is the space plane (reference plane) with the same x,y coordinate. It differents only z coordinate. Therefore, How can I calucate the volume of different plane ? Thank you very much.