Multi-dimensional acquisition of bipolar signals from a catheter

A medical apparatus, comprising:

• a probe, comprising:
• an insertion tube configured for insertion into a body cavity of a patient;
• and
• a basket assembly connected distally to the insertion tube and comprising a plurality of resilient spines having respective proximal and distal tips and comprising multiple electrodes arrayed along a length of each of the spines between the respective proximal and distal tips, such that the proximal tips of the spines are joined at a proximal end of the basket assembly, and the distal tips of the spines are joined at a distal end of the basket assembly, and the spines bow radially outward when the basket assembly is deployed in the body cavity, whereby the electrodes contact tissue in the body cavity;
• and
• processing circuitry, which is configured to acquire a first bipolar electrical signal from the tissue between first and second electrodes at first and second locations along a first spine of the basket assembly, the second electrode being adjacent to the first electrode on the first spine, and to acquire a second bipolar electrical signal from the tissue between the first electrode and a third electrode in a third location on a second spine of the basket assembly adjacent to the first spine, the third electrode being closest to the first electrode among electrodes on the second spine, a first axis between the first electrode and the third electrode extending at an oblique angle relative to a second axis extending between the first electrode and the second electrode, and to interpolate, based on the first and second bipolar electrical signals, a vectorial electrical property of the tissue along a third axis that passes through the first location and between the second and third locations.