1. Chief Technical Officer, Spatial Reference System Division, National Geodetic Survey, National Ocean Service, National Oceanic and Atmospheric Administration, N/NGS2, #8712, 1315 East-West Highway, Silver Spring, MD 20910-3282 (corresponding author).
2. Professor, Dept. of Civil Engineering, National Taiwan Univ., No. 1, Sec. 4., Roosevelt Rd., Taipei 10617, Taiwan.