1. An external control device for use with implantable neurostimulation leads, each having a plurality of electrodes, comprising: memory; a plurality of sets of estimated electrical parameter data stored in the memory, each set corresponding to a predetermined relative position between the neurostimulation leads; and a processor configured for comparing measured electrical parameter data with the estimated electrical parameter data of each the sets, and determining a relative position between the neurostimulation leads based on the comparison, the measured electrical parameter data having been measured in response to electrical energy transmitted to or from the electrodes of the neurostimulation leads.