Journal of Surveying Engineering

Rising Lake Michigan water levels were found to negatively influence the amount of wetlands and beaches in the Straits of Mackinac area of Lake Michigan. The effects of long‐term fluctuation in water levels were determined from measurements of wetlands and beaches on seven sets of historical aerial photographs (1938–1980). Analysis of aerial photographs demonstrated a 380 acre (154 ha) difference in total wetland and beach areas at the highest lake level sampled, as compared to the total at the lowest lake level sampled, or a range of 4 ft (1.2 m). A linear model between total wetland and beach areas and water levels $(R^2=0.93)$ indicated an increase of 1 ft (0.3 m) would result in a decrease of 80 acre (32 ha) or 18% of the 439 acre (178 ha) of wetlands and beaches in the study area. This methodology, which includes measurements from historical aerial photographs, acquisition of small format aerial photographs, and determination of local hydrological conditions, was useful for quantifying change in these lacustrine wetlands.

Conventionally, the determination of astronomic azimuth involves the synchronization of the observations with a radio time signal or the measurement of zenith distances which are subject to refraction errors. A mathematical model is developed which is dependent upon time differences (not absolute time) and horizontal angles (nearly refraction‐free) between pairs of stars. Error analysis indicates that an optimum star pair includes Polaris and any second star whose azimuth is at least moderately changing. Field tests indicate that the azimuth of Polaris may be determined to within 0.6 seconds of arc. The formation and solution of the necessary equation may be implemented on a programmable calculator.

Buildings that are used in oil field operations at Prudhoe Bay, Alaska are built in warm water ports thousands of miles away. These buildings (modules) are fabricated on top of columns (stub columns) that have square flat plates at the bottom (stub column base plates). At Prudhoe Bay, the modules are placed at various drill sites, flow stations, and piping facilities. They are supported by large diameter metal pilings that have square flat plates (pile caps) on the top. Modules weigh up to 5,000 tons (2,300 metric tons) and may be supported by 50 pilings or more. The planes of the corresponding flat plates, the pile cap, and the stub column usually are not parallel. They are required to be parallel, however, to ensure the best bearing surface. Parallel planes are formed on site by the insertion of two identical circular tapered shims between the flat plates before the module is set in place. A program that finds the correct orientation of the tapered shims through a least squares fitting procedure is presented here.

A program system is developed allowing the adjustment of one, two and three dimensional geodetic networks while taking into account accuracy and reliability aspects. The aims of the system are to enable the operator to improve and to optimize given measurement concepts and to provide a powerful tool for adjustment and blunder detection. This paper describes the basic theory, stressing especially external reliability, free adjustment of a net and the combination of pre‐analysis and adjustment. The examples and numerous adjustments of nets confirm that the system is capable of fulfilling the imposed requirements. It is flexible enough to be extended to cater for any further type of observations or additional unknowns. The flexibility was achieved by a high modularization of the program using a data management scheme which is valid for a whole set of different application programs.

The Global Positioning System provides relative positions to 1–2 ppm with anrobservation time of 2–3 hr. The quality does not depend on weather; there is no intervisibility between stations required. The inner and minimal constraint solutions are introduced for the quality control of GPS vector observation. The problems of network maintenance assume new significance in view of the high quality of GPS observations. The 3‐ and 2‐dimensional transformations are introduced for implementing GPS vector observations into existing networks. The 3‐dimensional transformation is parameterized by scale, 3 translations, and 3 rotations. This transformation is unique, i.e., the same a posteriori variance of unit weight and residuals are obtained, even though there are different choices for the rotations. The 2‐dimensional transformation is carried out on the ellipsoid. A combined adjustment of all terrestrial and GPS observations of a local area avoids dealing with network distortions. The primary quantities are the observations and not the coordinates.

A classification of interactive graphic systems, currently used to prepare plans and maps in surveying practice, is presented. The first generation of systems are graphics editors storing drawings that can be graphically changed and redrawn. A second generation of systems provides the same functionality as the first, but the user can add certain types of information to the graphical elements (e.g., tube diameter or material). The state‐of‐the‐art third generation of systems internally stores models of reality. Drawings and reports produced in varying formats are just operations to make these internal models visible to the user. Such systems can automatically maintain constraints on the model during changes. This classification seems to reflect a very general trend in computer applications toward systems that integrate an increasing amount of knowledge about reality.