1. A method comprising: capturing, by a camera, images of a scene having overlapping fields of view from image to image; recording an absolute global position of the camera at a time of capture for each of the images; identifying object points in the images that are common to the images from image to image; estimating parameters representing the positions of the object points relative to the absolute global positions of the camera using the absolute global positions of the camera without using input orientation data measured by a sensor associated with the camera representing orientations of the camera on capture of the images to set initial estimates of the orientations of the camera on capture of the respective images; deriving a target object point based on the parameters representing the positions of the object points relative to the absolute global positions of the camera; and deriving the absolute global position of the target object point based on the absolute global positions of the camera.