Mission Planning for High Precision RTK GPS Surveying Using Accurate Digital Terrain Information

Rodney Walker and Jizhang Sang

Abstract:	The information age has bought with it the ability to collect and manage extraordinarily vast amounts of data. Very accurate and detailed geographic information is now readily available to many surveyors at the touch of a button. Many mine sites, cities and other commercial areas have full 3D elevation models available on-line, usually obtained through aerial digital photogrammetry techniques. Commercial digital photogrammetric systems can attain very high vertical accuracy’s, of the order of l/10000 of the flying height of the original photographs. This commonly equates to vertical accuracy’s of less than 5Ocm, where the horizontal grid resolution is only limited by the processing power of the machine used to create the 3D model. With more emphasis placed on GPYGLONASS availability in harsh environments, it is useful for navigation and precise positioning purposes to have this terrain information available (in pm-mission) to the surveyor. Typically when performing a high precision GPS survey in a harsh environments it is desirable to be able to schedule the mission for a time period when the satellite availability is high and the DOP values are at a minimum. Even though the complete GPS satellite constellation provides good coverage for users at a 10’ mask angle, users operating in harsh environments where the 10” mask angle is not representative of the local terrain will see significant differences between the ideal satellite availability and the observed availability. This difference will affect the total system surveying accuracy. This paper shows how optimal survey mission planning can be made by exploiting the high accuracy 3D digital terrain models. Predictions can be made of the real satellite availability and DOP values for a chosen site, based on the real mask angles defined by the local terrain and obtained from the 3D model. Practical results were obtained in the field on an open cut mine which verify the predicted results. Also satellite signals that are diffracted can be rejected from the post mission analysis and satellite signals that are near a masking object can also be excluded to obtain the highest accuracy solution. Having access to this type of information is extremely convenient when a high precision survey is required to be. undertaken in harsh environments. The mission can be planned when suitable satellite availability and geometry is attainable, and satellite signals that may contain errors can be ignored in the post mission analysis phase. This paper shows exactly the results between the predicted satellite constellation and the observed satellite constellation, and also shows how vast improvements in survey accuracy on open cut mines can be made by consulting this type of information. This technique is invaluable for the mining surveyor looking to obtain a high precision survey in a typically harsh environment.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	367 - 373
Cite this article:	Walker, Rodney, Sang, Jizhang, "Mission Planning for High Precision RTK GPS Surveying Using Accurate Digital Terrain Information," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 367-373.
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