Method of locating a location of a portable device using a first light source, the portable device comprising an image sensor and an inertial measurement unit, the method comprising: - obtaining a first image comprising a first coded light source from the image sensor and substantially simultaneously obtaining orientation information indicative of the orientation of the portable device or the image sensor from the inertial measurement unit; - establishing a three-dimensional location of the first coded light source, using coded light detected from the first coded light source; and - computing the location of the portable device or image sensor based on the orientation information, the position of the first coded light source in the first image, a predetermined height estimate of the portable device or image sensor and the three-dimensional location of the first coded light source, characterized by the method further comprising subsequently continuing localization to compute an update to the location of the portable device by: detecting in a second image a second light source that does not emit coded light; obtaining subsequent information from the inertial measurement unit comprising heading information indicative of motion of the portable device in a heading direction; accessing map information comprising three-dimensional location data, providing three-dimensional locations of light sources; establishing a candidate light source comprised in the map information, based on the location computed based on the position of the first coded light source in the first image and on the heading information; and computing an updated location of the portable device or image sensor, under the assumption that the second light source corresponds with the candidate light source, by using: the subsequent information from the inertial measurement unit; the location of the candidate light source in the second image; the predetermined height estimate of the portable device; and the location of the candidate light source identified by the map information. - obtaining a first image comprising a first coded light source from the image sensor and substantially simultaneously obtaining orientation information indicative of the orientation of the portable device or the image sensor from the inertial measurement unit; - establishing a three-dimensional location of the first coded light source, using coded light detected from the first coded light source; and - computing the location of the portable device or image sensor based on the orientation information, the position of the first coded light source in the first image, a predetermined height estimate of the portable device or image sensor and the three-dimensional location of the first coded light source, characterized by the method further comprising subsequently continuing localization to compute an update to the location of the portable device by: detecting in a second image a second light source that does not emit coded light; obtaining subsequent information from the inertial measurement unit comprising heading information indicative of motion of the portable device in a heading direction; accessing map information comprising three-dimensional location data, providing three-dimensional locations of light sources; establishing a candidate light source comprised in the map information, based on the location computed based on the position of the first coded light source in the first image and on the heading information; and computing an updated location of the portable device or image sensor, under the assumption that the second light source corresponds with the candidate light source, by using: the subsequent information from the inertial measurement unit; the location of the candidate light source in the second image; the predetermined height estimate of the portable device; and the location of the candidate light source identified by the map information. detecting in a second image a second light source that does not emit coded light; obtaining subsequent information from the inertial measurement unit comprising heading information indicative of motion of the portable device in a heading direction; accessing map information comprising three-dimensional location data, providing three-dimensional locations of light sources; establishing a candidate light source comprised in the map information, based on the location computed based on the position of the first coded light source in the first image and on the heading information; and computing an updated location of the portable device or image sensor, under the assumption that the second light source corresponds with the candidate light source, by using: the subsequent information from the inertial measurement unit; the location of the candidate light source in the second image; the predetermined height estimate of the portable device; and the location of the candidate light source identified by the map information.