- In surveying and geodesy, a datum is a reference system or an approximation of the Earth's surface against which positional measurements are made for computing locations. Horizontal datums are used for describing a point on the Earth 's surface, in latitude and longitude or another coordinate system.
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A horizontal datum is a specified coordinate system for a collection of positions on the surface of the earth. Traditionally, horizontal datums have used classical surveying methods (i.e. Measuring distances and angles through triangulation surveys) to best fit to the surface of the earth. A geometric datum is a coordinate system for collection ...
A horizontal datum provides a reference frame for coordinates on Earth. A long time ago, surveyors put brass monuments in the Earth with precise X, Y locations. When these monuments were combined together using a technique called triangulation, this formed our horizontal datum.
Horizontal datums are used for describing a point on the Earth's surface, in latitude and longitude or another coordinate system. Vertical datums are used to measure elevations or underwater depths. Horizontal datum. The horizontal datum is the model used to measure positions on the Earth.
Horizontal datums define the geometric relationship between a coordinate system grid and the Earth's surface. Because the Earth's shape is complex, the relationship is too. The goal of this section is to explain the relationship.
At its most basic level of definition, the horizontal datum is a collection of specific points on the Earth that have been identified according to their precise northerly or southerly location (latitude) and easterly or westerly location (longitude).
The horizontal datum is the one that is used in measuring a specific position on the earth's surface in coordinate systems such as latitude and longitude.
- Amanda Briney
Jul 12, 2018 · The North American Datum of 1927 (NAD 27) is "The horizontal control datum for the United States that (was) defined by (a) location and azimuth on the Clarke spheroid of 1866, with origin at (the survey station) Meades Ranch." ... The geoidal height at Meades Ranch (was) assumed to be zero.
The term horizontal datum is used because it is more easily flattened into 2 dimensions and more useful for finding locations on a flat plane (compared to a vertical datum). As in the ESRI post you referenced (image below), the Earth's surface is very uneven, so modeling this very difficult.
A horizontal datum provides a frame of reference as a basis for placing specific locations at specific points on the spheroid. Geodesists use a horizontal datum as the model to translate a spheroid / ellipsoid into locations on Earth with latitude and longitude lines. Geodetic datums form the basis of coordinates of all horizontal positions on Earth.
NAD 23 CONUS datum is one of these terrestrial based datums established from a triangulation station in Meades Ranch, Kansas. As space based surveying came into use, a standardized datum based on the center of the earth and an ellipsoid the was a good fit to the entire surface of the earth was developed.