Method and apparatus for measuring displacement of object using GPS

Relative vector between an observation receiver located at an object and a reference receiver are divided into long period variation components not dependent on object displacements and short period variation components dependent on object displacements, and the short period variation component are represented by x, y and z axis components of unit vectors from the reference receiver toward the satellite. Then, carrier phases between at least three GPS satellites and the receivers are measured, and these measurement data are passed through a band pass filter to extract short period phase components corresponding to the short period variation components of the relative vectors. Next, at least three receiver to receiver single differences between the receivers and the GPS satellites are found for the short period phase components, and axial components of the short period variation components of the relative vectors are found by computation based on said at least three receiver to receiver single differences.