Grid function at certain point

Hello everyone,

I am a newbee and solved Navier Stokes using NG solve. To test the quality of the velocity solution (defined by GridFunction, gfu = GridFunction(fes), and the velocity is defined by gfu.components[0] ) I would like to check the value of it at a certain point.

How do I extract the solution value of velocity at a certain point?

Thanks in advance.

see the docu on CoefficientFunctions:
a GridFunction is a CoefficientFunction as well (by inheritance)