Abstract
Navigation and determining the ship’s position depend on global satellite systems, primarily GPS global positioning systems. In maritime practice, the definite ship position is considered the most probable position and will be the center of the probability circle containing the ship's position. However, this is not entirely accurate because it depends on many factors such as deviation of the geodetic system, the accuracy of charts, ... On the other hand, the radius of error of probability circle that containing the ship's position is a scalar area, depending on many factors,... Therefore, the determination of probability location with the highest accuracy is a rather complex problem. In this paper, the author proposes a method of determining the probability area containing the actual ship position and its orientation in order to improve safety in maneuvering and navigation at sea for Vietnam coastal waters.