surveying iii (topographic and geodetic surveys) - Modern Prepper

necessary to determine approximate orthometric elevations from relative GPS observations.a. The baseline reduction process provides the raw relative position coordinates that are used in a3D GPS network adjustment. Depending on the manufacturer's software, each reduced baseline containsvarious orientation parameters, covariance matrices, and cofactor or correlation statistics that may beused in weighting the final network adjustment. Most least squares adjustments use the accuracy orcorrelation statistics from the baseline reduction; however, other weighting methods may be used in aleast squares or approximate adjustment.b. The adjustment technique employed (and the time devoted to it) must be commensurate with theproject's accuracy requirements. Care must be taken to prevent the adjustment process from becoming aproject in itself.c. There is no specific requirement that a rigorous least squares adjustment be performed ontopographic surveys, whether conventional, GPS, or mixed observations. Traditional approximateadjustmentmethods may be used in lieu of the least squares method and provide comparable, practicalaccuracy results.d. Commercial software packages designed for higher-order geodetic-densification surveys oftencontain a degree of statistical sophistication that is unnecessary for engineering survey controldensification (such as second-order or less). The distinction between geodetic surveying andengineering surveying must be fully considered when performing GPS-S adjustments and analyzing theresults.e. Connections and adjustments to existing control networks, such as the National GeodeticReference System (NGRS), must not become independent projects. It is far more important to establishdense and accurate local-project control than to consume resources tying into first-order NGRS pointsthat are miles from the project. Engineering, artillery, construction, and property/boundary referencingrequires consistent local control with high relative accuracies. Accurate connections and references todistant geodetic datums are of secondary importance (the exception being projects in support of militaryaviation operations). The advent of GPS-S technology has provided a cost-effective means of tyingpreviously poorly connected projects to the NGRS and simultaneously transforming the projects to thenewly defined NAD 83. When performing (adjusting) these connections, do not distort or warp longestablishedproject reference points.5-48. Survey Accuracy. The accuracy of a survey (whether performed using conventional or GPSmethods) is a measure of the difference between observed and true values (such as coordinates, distance,or angle). Since the true values are rarely known, only estimates of survey accuracy can be made. Theseestimates may be based on internal observation closures (such as on a loop traverse) or connections withpreviously surveyed points assumed to have some degree of reliability.a. A loop traverse originating and ending from a single point will have a misclosure whenobservations (such as EDM traverse angles or distances or GPSEN0593 5-42