Barometric altimeter doesn't provide absolute altitude because atmosphere always varies over time and geographical location. Also, Global Navigation Satellites System such ad GPS, GLONASS has geometric error, the altitude information is not available. In this paper, we used accurate information from RTK reference station and calculated absolute altitude by difference value of pressure data at reference station and mobile station. 3-D positioning system is drawn by calculated absolute altitude data and reference information. This paper introduces a 3-D positioning algorithm using absolute altitude etermination method and evaluates the algorithm by real field tests. We expect to help position determination technique at the field of firefighting and construction.

Keywords: absolute altitude determination, RTK reference station, 3-D positioning algorithm