A localization system, comprising: a first localization element (17, 52, 54, 56) and a second localization element (17, 52, 54, 56); a localization processor configured: to receive as input a first localization signal from the first localization element (17, 52, 54, 56) carried by a catheter including a plurality of localization elements (17, 52, 54, 56) and a second localization signal from the second localization element (17, 52, 54, 56) carried by the catheter; to resolve the first localization signal into a first in-phase component (100, 102, 104, 106) reflective of a position of the first localization element (17, 52, 54, 56) within a localization field and a first quadrature component (200, 202, 204, 206); and to resolve the second localization signal into a second in-phase component (100, 102, 104, 106) reflective of a position of the second localization element (17, 52, 54, 56) within the localization field and a second quadrature component; and a state detection processor configured: to receive as input the first quadrature component (200, 202, 204, 206) and the second quadrature component (200, 202, 204, 206); and characterised in that the state detection processor is further configured: to detect whether the second localization element (17, 52, 54, 56) is within or outside of an introducer sheath by comparing the second quadrature component (200, 202, 204, 206) to the first quadrature component (200, 202, 204, 206). a first localization element (17, 52, 54, 56) and a second localization element (17, 52, 54, 56); a localization processor configured: to receive as input a first localization signal from the first localization element (17, 52, 54, 56) carried by a catheter including a plurality of localization elements (17, 52, 54, 56) and a second localization signal from the second localization element (17, 52, 54, 56) carried by the catheter; to resolve the first localization signal into a first in-phase component (100, 102, 104, 106) reflective of a position of the first localization element (17, 52, 54, 56) within a localization field and a first quadrature component (200, 202, 204, 206); and to resolve the second localization signal into a second in-phase component (100, 102, 104, 106) reflective of a position of the second localization element (17, 52, 54, 56) within the localization field and a second quadrature component; and to receive as input a first localization signal from the first localization element (17, 52, 54, 56) carried by a catheter including a plurality of localization elements (17, 52, 54, 56) and a second localization signal from the second localization element (17, 52, 54, 56) carried by the catheter; to resolve the first localization signal into a first in-phase component (100, 102, 104, 106) reflective of a position of the first localization element (17, 52, 54, 56) within a localization field and a first quadrature component (200, 202, 204, 206); and to resolve the second localization signal into a second in-phase component (100, 102, 104, 106) reflective of a position of the second localization element (17, 52, 54, 56) within the localization field and a second quadrature component; and a state detection processor configured: to receive as input the first quadrature component (200, 202, 204, 206) and the second quadrature component (200, 202, 204, 206); and characterised in that the state detection processor is further configured: to detect whether the second localization element (17, 52, 54, 56) is within or outside of an introducer sheath by comparing the second quadrature component (200, 202, 204, 206) to the first quadrature component (200, 202, 204, 206).