Depending on different types of users, several algorithms, one of which combines Doppler and range measurements for positioning computation and which is called the D-R algorithm, can be used in software design in a satellite positioning system. The D-R algorithm can be selected for a stationary user in certain circumstance where only few satellites can be tracked simultaneously due to shielding. This paper studies the characteristics of geometric dilution of precision (GDOP) in the D-R algorithm and tries to give an outline of this algorithm. The simulation results given are instructive for positioning system constellation design as well as receiver positioning software design.