NOVELTY - The method (400) involves utilizing an antenna configuration comprising a pair of relatively closely spaced antennae and other pairs of distant antennae. The closely spaced pair provides a short baseline having an integer ambiguity that may be searched exhaustively to identify the correct set of integers. This baseline is then used as a priori information to aid the determination of longer baselines that, once determined, may be used for accurate run time attitude determination.    USE - For determining attitude of an object by determining inter-antenna baselines from radio wave phase measurements. E.g. for control and navigation of vehicles, aircraft, watercraft and spacecraft, or for determining a pointing direction for sighting devices or remote sensing devices, e.g. used to launch ballistic or propelled projectiles. Can also be used for identifying the physical shape and location of structures, e.g. to determine the shape and location of rigid surfaces or booms, or implements used to carry out physical placement or excavation. Can further be used to orient and point devices adapted to receive electromagnetic radiation such as antennae or solar panels.    ADVANTAGE - Enables reliable inter-antenna baseline determination.    DETAILED DESCRIPTION - The method involves identifying a first antenna and a second antenna located a distance D1 apart, and identifying a third antenna located a distance D2 from the second antenna. A first baseline between the first antenna and the second antenna is determined using a backward integer search procedure, and a second baseline between the second antenna and the third antenna is determined using a forward integer search procedure responsive to the first baseline. D1 at most 2.5 wavelengths of a carrier wave that emanates from a radio source such as a GPS satellite, and D2 at least 1.0 wavelengths of a carrier wave that emanates from a radio source such as a pseudolite. A third baseline is determined between a fourth antenna and one of the other antennae, using a forward integer search procedure responsive to at least one previously determined baseline.    INDEPENDENT CLAIMS are included for: (i) an apparatus for determining inter-antenna baselines from radio wave phase measurements; (ii) an antenna configuration used in the apparatus; and (iii) a GPS attitude system.    DESCRIPTION OF DRAWING(S) - The drawing shows an inter-antenna baseline determination process.    inter-antenna baseline determination process (400)