1. Chief Technical Officer, Spatial Reference System Division, National Geodetic Survey, National Ocean Service, National Oceanic and Atmospheric Administration, Silver Spring, MD 20910 (corresponding author).
2. Associate Professor, Dept. of Civil Engineering, National Taiwan Univ., Taipei 10617, Taiwan.
3. Deputy Director, National Geodetic Survey, National Ocean Service, National Oceanic and Atmospheric Administration, Silver Spring, MD 20910.