Numerical Integration Cylindrical Coordinates - Volume

This script computes a Volume Integral on a circle. It creates a spline from a set of data points, and computes a volume around a circle.

Simple program:
Enter a set of points.
Enter a set of coordinates for each point.
The program interpolates and creates a spline.
It then computes the volume integral of this spline, revolved around the axis of the circle.
This does not compute a line integral for the polynomial created by the data set. 
Reason: in order to compute a correct volume integral a correct cylindrical coordinates infinitesimal area element is used in the integral, and this means multiplying the argument of the integral by the radius coordinate variable, which in effect means increasing the degree of the polynomial from polyfit.
Test the example before by hand, the integral of X^2 multiplied by X over a radius, revolved by 2*pi.
INTEGRAL = ( x^2 ) * ( X dX d THETA )
The infinitesimal area element is dS = X * dX * dTHETA.
Remember that the interval of the function inside the integral is from X = 0 to X = 5, THETA from 0 to 2 pi.