Journal of Surveying Engineering

A surface-profile measurement system is introduced, with emphasis on the design and the measuring principles of the system. Originally developed for the measurement of imperfections in large-scale steel silos, the system consists of a measuring trolley, associated supporting equipment, and a software package. The measuring trolley, when pulled over a measured surface, continuously records the information on the geometric shapes of the surface. The recorded information is then used to calculate the profiles of the measured surface based on least-squares principles. The profile measurement system offers several advantages over existing profile measurement techniques, especially in determining the surface geometry of large engineering structures.

Geometric imperfections in thin-shell structures such as silos and tanks need to be measured to assess the buckling strength of the structures, and to develop new structure design criteria. A number of difficulties are associated with the task of imperfection measurements in such structures. This paper describes a new technique that uses conventional survey instrumentation as well as a specifically designed surface profile measurement apparatus. The profile data and survey observations are combined in a common least-squares adjustment model. The measured silo-wall imperfections are analyzed using a double Fourier series to determine dominant imperfection modes. The new silo and tank measurement technique offers many advantages over existing methods and has been successfully employed for the measurement of three large grain silos. Results from the measurement test are given as an example.

With readjustment of the North American Datum of 1927 (NAD27) and promulgation of a new datum, the North American Datum of 1983 (NAD83), along with refinements to the network based on high precision Global Positioning System (GPS) surveys, it became important for the user community to be able to convert coordinate values from one datum to the other while preserving the inherent quality of existing information. Accordingly, a project was undertaken to model local distortions between the datums with sufficient refinement that coordinate values on the NAD27 datum could be readily and reliably transformed to NAD83 values and so that NAD83 coordinate values could be similarly transformed to NAD27 values. The present paper describes successful determination of transformation parameter sets to be used in various areas of a seven-county 7,000 km ² (2,700 mi ² ) region, in southeastern Wisconsin, to model localized distortion. The result is that, using the computed parameters and standard transformation equations, coordinate values for surveyed points throughout the region can be readily and reliably converted from one datum to the other.