for (myNodeData = myFaceset.begin(); myNodeData != myFaceset.end(); myNodeData++) {
// evaluate voltage at each node I
// set up X_T function for integration: k*chargeDensity/||x_I - x_s||
// integral is approximated in two parts:
// 1) near part with all faces within r < rcrit evaluated as 2 * pi * rcrit * k sigma A/A0, A is area of this region and A0 = pi * rcrit^2, so 2 k sigma A / rcrit
// 2) far part evaluated using Gaussian quadrature on faceset