1. A method of a volume of activation (VOA) providing machine to provide a VOA of a stimulation electrode leadwire, comprising: calculating, by a processor of the machine, a VOA for each of a plurality of sets of parameter settings of the leadwire; storing in a database each of the calculated VOAs in association with the respective set of parameter settings for which it was calculated; for a selected electrode configuration, plotting voltages at anatomical locations; for each of a plurality of waveforms, determining an amplitude threshold for activation at various ones of the locations; performing a curve fitting on the threshold values determined for the plurality of waveforms, the curve fitting resulting in a voltage threshold equation that provides a voltage threshold for a given pulse width, amplitude, and impedance; obtaining a further set of parameter settings of the leadwire; determining, by the processor, a VOA for the obtained set of parameter settings based on the stored VOAs; and outputting, by the machine, the determined VOA; wherein: the obtained set of parameter settings includes an electrode configuration, a pulse width, and an amplitude; and the determining of the VOA for the obtained set of parameter settings includes: obtaining a voltage threshold for the pulse width and amplitude of the parameter settings using the function; and applying the voltage threshold to voltages plotted for the obtained set of parameter settings.