An Error Analysis of Range-Azimuth Positioning.

Pointing error standard deviations for two theodolites, the Wild T-2 and Odom Aztrac, were determined under conditions closely approximating those of range-azimuth or azimuth-azimuth hydrographic surveys. Pointing errors found for both instruments were about 1.3 meters, and were independent of distance. No statistical difference between the errors of the two instruments was found. The accuracy of the interpolation methods used by the National Ocean Service NOS for range-azimuth positioning were investigated, and an average inverse distance of about 2.5 meters was observed between interpolated positions and corresponding observed positions. The overall range-azimuth position errors of the two theodolites were then compared to positioning standards of NOS and the International Hydrographic Organization, using assumed ranging standard deviations of 1.0 and 3.0 meters. Both instruments met all standards except the NOS range-azimuth standard for 15,000 scale surveys. Interpolated positions may fail to meet more of the standards because of additional inherent error. Author