Simplified Transformation between NAD27 and NAD83 in Southeastern Wisconsin

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.