Ground control should be established to a level of accuracy commensurate with that specified for the final map product. Careful planning and analysis of the basic control and photo control ground surveys should be performed by the contractor to ensure that sufficient accuracy will be obtained throughout the
project area to meet map compilation and aerotriangulation criteria.
1. Accuracy required
project area to meet map compilation and aerotriangulation criteria.
1. Accuracy required
Field surveys to establish project control should ideally originate from higher order control established by USACE, NGS, USGS, or local agencies. Field surveys should be designed for the lowest order survey that will meet project requirements, as specified in Table 2-4. As the accuracy standard
increases, the cost of the survey will increase significantly. As a rule of thumb, the accuracy of the horizontal photo control should be twice the horizontal map accuracy to be produced, and the vertical photo control accuracy should be as accurate as the spot elevation accuracy to be produced. The accuracy of a given photo control point is the propagated error in the basic control survey points combined with the error contributed by the survey to connect to the photo control point.
2. USACE standards
increases, the cost of the survey will increase significantly. As a rule of thumb, the accuracy of the horizontal photo control should be twice the horizontal map accuracy to be produced, and the vertical photo control accuracy should be as accurate as the spot elevation accuracy to be produced. The accuracy of a given photo control point is the propagated error in the basic control survey points combined with the error contributed by the survey to connect to the photo control point.
2. USACE standards
USACE standards and guidelines for control surveys are presently under development. Until the USACE standards are available, the FGCC standards discussed in c below should be used to plan and execute the basic and photo control surveys for photogrammetric aerotriangulation and mapping.
3. FGCC standards
3. FGCC standards
Standards and Specifications for Geodetic Control Networks (FGCC 1984) may be used to plan and execute the basic and photo control surveys for photogrammetric aerotriangulation and mapping. FGCC relative accuracy standards for horizontal and vertical control are shown in Tables 5-2 and 5-3. The FGCC document also gives procedural specifications for triangulation, trilateration, traversing, Global Positioning System (GPS) and Doppler positioning, photogrammetry, and leveling field survey methods. These specifications should be followed to ensure that the accuracy standard will be met.
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