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A set of parameters and control points used to accurately define the three-dimensional shape of the Earth (e.g., as a spheroid). The corresponding datum is the basis for a planar coordinate system.

- Defines the origin, orientation and scale of the coordinate system and ties it to the earth, ensuring that the abstract mathematical concept 'coordinate system' ...

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GIS Dictionary
Definitions for GIS terms related to operations such as analysis, GIS modeling and web-based GIS, cartography, and Esri software.

Map Datums
A datum describes the model that was used to match the location of features on the ground to coordinates and locations on the map. Maps all start with some form of survey.

: A math model which depicts a part of the surface of the earth. Latitude and longitude lines on a paper map are referenced to a specific map .

Reference Datum
A reference datum is a known and constant surface which can be used to describe the location of unknown points. On Earth, the normal reference datum is sea level.

You are publishing a tiled map service using the ArcGIS Online/Google Maps/Bing Maps tiling scheme and there is no transformation from your data frame's to WGS 1984 Major Auxiliary Sphere.

A reference location or elevation which is used as a starting point for subsequent measurements. Sea level is a datum for elevation measurements.

4-1. The earth is an ellipsoid, not a sphere, flattened slightly at the poles and bulging somewhat at the equator.

Datum, Spheroids and Ellipsoids
Unlike local surveys, which treat the Earth as a plane, the precise determination of the latitude and longitude of points over a broad area must take into account the actual shape of the Earth.

s 1 - the Basics
A is a system which allows the location of latitudes, longitudes and heights to be identified onto the surface of the Earth. As s is a jargon rich subject it is recommended that you read this section first.

A datum is a mathematical surface on which a mapping and coordinate system is based.

: In mapping, a numeric or geometric quantity which serves as a reference or base to accurately define other quantities.

Datum - A reference surface for a particular coordinate system. Defines the mathematical relationship by which a feature relates to its original surface in a specific coordinate system.

- "1. Any point, line, or surface used as a reference for a measurement of another quantity. 2. A model of the earth used for geodetic calculations" (Bonham-Carter, 1994, p. 356).

Datums are sets of parameters and ground control points defining local coordinate systems.

For highly precise maps of smaller regions, the basic ellipsoidal shape can not be ignored. A geodetic is a set of parameters (including axis lengths and offset from true center of the Earth) defining a reference ellipsoid.

The Datum Selection Option
The selection of the DRG Clipper Button will prompt the user to identify the current datum of the 24K DRG files as shown below.

A point, line, or surface reference from which coordinate systems are derived for surveying and mapping.
DNR Louisiana Department of Natural Resources.

Datum transformations using Molodensky equations (implemented in most geo-software) are becoming increasingly important, because of the growing use of GPS data.

conversions are automatically handled by the PROJ.4 library if "+" setings are specified on both the input and output projections on the command line.

Datum Notes:
Spatial data are referenced to a horizontal datum and a vertical datum, both of which are based on a mathematically calculated shape of the earth.

s can be vertical, horizontal, or complete. Vertical s deal primarily with elevation and are usually developed to supplement existing s.

Datum - A point, line or surface selected as the origin or reference for measurements. A datum can be mathematically defined (e.g. the Earth's ellipsoid) or established by field observations (e.g. the mean sea level).

The established in 1929 by the U.S. Coast and Geodetic Survey as the surface against which elevation data in the United States is referenced. Referenced by: North American Vertical of 1988; Elevation; Sea Level of 1929.

Geodetic Datum: A set of parameters defining co-ordinate systems for all or parts of the earth. These datums have been refined and revised over time. NAD 27 is the North American datum for 1927, for example.

These materials were developed by Peter H. Dana, Department of Geography, University of Texas at Austin, 1995. These materials may be used for study, research, and education in not-for-profit applications.

Multiple datum LRS and color coding of complex infrastructure objects often result in misleading or incorrect computation, identified by Sutton (1996) as network pathologies.

Geodetic s
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Changing datums (for example, from NAD 27 to NAD 83) can be difficult or cumbersome.
Projections are usually implemented using power series approximations that might be inadequate for high precision work.

Geocentric relate coordinates to the earth's center of mass. Such have been improved by modern satellite data.

(singular: datum) information collected during a scientific study.
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North American Datum 1983
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data update cycle Source: GETIS glossary Data update interval dataset series Source: ISO 19115; ISO 19113; ISO 19114 Collection of datasets sharing the same product specification Defines the origin, ...

Map Projections and Datum and Coordinate Systems Overview, by Peter H. Dana - part of the The Geographer's Craft project.
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Typically consists of a projection or a system of projection zones plus a geodetic and ellipsoid. NDVI p.

NDVI = (IR - Red)/(IR + Red) North American Datum (NAD) Datums used as a basis for large scale mapping, particularly NAD27 and NAD83 Northings The y-coordinates in a plane-coordinate system; see eastings.
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Then I went through the source code to try to find out where the CH1903 came into the picture. The source code is just about unreadable, being made up mostly of #defines for all the functions.

See also: See also: Map, Geographic, Coordinate, Information, Surface

GIS  Date line  DBI

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