Position determining unit and a method for determining a position of a land or sea based object

Position determination unit (800) for an object based on land or sea, said position determination unit comprising or having access to a three-dimensional map (802) comprising three-dimensional georeferenced position data, said position determination unit comprising furthermore map part selection means (803) for selecting a part of the three-dimensional map (802) to obtain a georeferenced position associated with the selected part, wherein the map part selection means comprise a user interface for manually selecting the part of the three-dimensional map, at least one measuring instrument (805) arranged to obtain bearing and / or distance information comprising at least two values measurement or at least three measurement values ​​referring to the object based on land or sea, and a calculation and control unit (804) arranged to refer each obtained bearing and / or distance information to a corresponding obtained georeferenced position and determine a geographical position of the object based on land or sea - in two dimensions on the basis of the Heading and / or distance information, comprising at least two measurement values, and the corresponding georeferenced positions obtained, or - in three dimensions based on the heading and / or distance information, comprising at least three measurement values, and the corresponding obtained georeferenced positions, in which the calculation and control unit (804) is arranged to receive second position information regarding the land or sea based object from a second source (808) which is a radio based global positioning system, e.g. GPS, to determine a difference between the second position information obtained from the second source (808) and the determined geographical position of the object based on land or sea, and - detect an uncertainty in second position information obtained when the difference exceeds a predetermined value .