Control surveys

North American Datum (NAD) Readjustment Project . The NAD readjustment project of the National Geodetic Survey (NGS) consists of three major tasks: the validation of all field projects, the validation of individual blocks, and the solution of the equations associated with each observation. Associated tasks include: researching mathematical models, defining detailed procedures, and developing required software. The validation of 4,890 field projects involved the keying of 2.5 million direction observations, the reprocessing of 60,000 electronic distance measurements, and the separate least‐squares adjustment of each field project. Block validation consists of the systematic analysis of observational data within more than 800 blocks. This task began in July 1982, and is expected to continue for 2 years. The partitioning of the U.S. horizontal network into blocks, and the systematic reduction of the equations by the Helmert blocking method, represents the last task of the project. Block validation testing began in the fall of 1982.