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| Provisional South American Datum | |
|---|---|
| Name | Provisional South American Datum |
| Abbreviation | PSAD |
| Region | South America |
| Introduced | 1969 |
| Datum origin | Belo Horizonte |
| Ellipsoid | International 1924 |
| Area | South America |
Provisional South American Datum The Provisional South American Datum was a continental geodetic datum established to provide a common horizontal reference for mapping and surveying across Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay, and Venezuela. Developed during cooperative programs involving national mapping agencies, the datum served as a regional standard during the late 20th century to harmonize control from disparate national grids used in projects led by organizations such as the International Union of Geodesy and Geophysics, the Pan American Institute of Geography and History, and the Interamerican Geodetic Survey.
PSAD originated from multinational efforts after conferences attended by delegates from the Instituto Brasileiro de Geografia e Estatística, Instituto Geográfico Nacional (Argentina), Instituto Geográfico Nacional (Chile), and surveying authorities from Peru and Colombia. The initiative followed technical cooperation programs with the United States Army Map Service, the U.S. Agency for International Development, and participation by members of the Royal Institution of Chartered Surveyors. Early field campaigns referenced classical triangulation schemes influenced by work from the Ordnance Survey and lessons from continental adjustments like the European Datum programs. Major workshops in cities such as Brasília, Buenos Aires, and Lima led to adoption of a common ellipsoid and provisional origin to reconcile legacy datums including national datums based on local astronomical stations and triangulation of the 19th century.
The datum used the International 1924 ellipsoid (also known as the Hayford ellipsoid) with defined semi-major axis and flattening consistent with contemporary international practice and recommendations from the International Association of Geodesy. A fixed origin near Belo Horizonte provided a pragmatic continental reference point, while the geodetic latitude and longitude convention followed the Greenwich Meridian for longitude origin. Parameters included standard parallels for map projections and projection definitions compatible with Transverse Mercator implementations used by national mapping agencies. The PSAD parameter set was disseminated in technical bulletins circulated to institutions like the National Geospatial-Intelligence Agency and regional cartographic schools.
Implementations of PSAD occurred in phased realizations recorded at specific epochs reflecting the time of observation and adjustment. Early realizations coincided with epoch dates tied to large-scale trilateration campaigns in the 1960s and 1970s, with subsequent refinements in later decades. Adjustments referenced geodetic stations such as long-established observatories in Rio de Janeiro, Bogotá, and Quito, and were synchronized with astronomical time standards maintained by agencies like the International Bureau of Weights and Measures and national observatories. The shift from PSAD realizations to modern reference frames paralleled global initiatives exemplified by the creation of the International Terrestrial Reference Frame.
PSAD depended on a continental network of primary and secondary control points established through triangulation, trilateration, and later electronic distance measurement campaigns. Notable control stations included monuments near Manaus, La Paz, Sucre, and coastal benchmarks at Valparaíso and Montevideo. These points were integrated into national cadastral programs maintained by institutions such as the Servicio Geográfico del Ejército (Spain) through technical exchanges and by Latin American agencies like the Dirección General de Catastro offices. Survey markers were often tied to tide gauge records at ports like Callao and Buenos Aires to assist in geoid and sea level studies connected with the Permanent Service for Mean Sea Level.
To facilitate interoperability with national datums and later global frames, transformation parameters (including three-parameter and seven-parameter Helmert transformations) were published for converting coordinates between PSAD and local systems such as the Datum Montevideo, MAGNA (Colombia), and legacy grids used by the Instituto Geográfico Nacional (Peru). Software toolchains in use by agencies like Esri and projects supported by the United Nations adopted transformation libraries to handle datum shifts, while researchers compared PSAD transformations against results from Global Navigation Satellite Systems including GPS networks and campaigns coordinated by agencies such as NASA and the European Space Agency.
PSAD supported topographic mapping, cadastral surveys, transportation planning, and resource management across South American nations. Cartographic products for use by ministries and regional planners adhered to PSAD coordinates for highway alignments, basin hydrology studies in the Amazon Basin, and infrastructure projects in urban centers including São Paulo, Santiago, and Medellín. Academic research at universities such as the University of São Paulo and Pontificia Universidad Católica de Chile used PSAD-referenced datasets for geological mapping and tectonic studies of the Andes.
While PSAD improved continental consistency, limitations arose from using a best-fit single ellipsoid and from tectonic motions across the Nazca Plate, South American Plate, and regional crustal deformation. Relative accuracies were sufficient for regional mapping but inadequate for high-precision geodetic applications that later relied on continuous GNSS networks and the International Terrestrial Reference Frame. Successor initiatives and national modernization programs migrated control to newer datums and realizations, incorporating satellite geodesy methodologies championed by organizations like the International GNSS Service and regional projects coordinated by the Pan American Institute of Geography and History.
Category:Geodetic datums Category:Cartography of South America Category:Surveying