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Datum
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.


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

Datum
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GIS Dictionary > datum
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.

Datum: 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 datum.

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 datum transformation from your data frame's datum to WGS 1984 Major Auxiliary Sphere.

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

DATUMS
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.

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

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

Datum: 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.

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

Datums
A datum is a starting point for locating features on the Earth's surface; it is the origin point of a coordinate system. It defines the position of the ellipsoid (or spheroid) relative to the Earth's center.

The Datum
For highly precise maps of smaller regions, the basic ellipsoidal shape can not be ignored. A geodetic datum 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.

Datum 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.

Datum conversions are automatically handled by the PROJ.4 library if "+datum" 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.

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

Datum
Point, line or surface used as a reference for a measurement of another quantity. Point, line, or surface used as a reference (i.e., surveying, mapping, or geology).

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 datum 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 Datum of 1988; Elevation; Sea Level Datum 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.

Geodetic Datum
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 Datums
Distance Between Degrees
Topo Maps
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Latitude and Longitude Video ...

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

(singular: datum) information collected during a scientific study.
data capture
Noun ...

Land Surface Datum; Lands and Survey Div. (Trinidad and Tobago)
LSDP
Landsat Signature Development Program (software) ...

North American Datum 1983
NAPLPS
North American Presentation Level Protocol Syntax ...

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 datum Defines the origin, ...

The global WGS84 datum (i.e., World Geodetic System of 1984) uses the center of the earth as the origin of the GCS and is used for defining locations across the globe.

Map Projections and Datum and Coordinate Systems Overview, by Peter H. Dana - part of the The Geographer's Craft project.
Return to The Map Projection Home Page ...

Typically consists of a projection or a system of projection zones plus a geodetic datum 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.
O ...

Then I went through the source code to try to find out where the CH1903 datum came into the picture. The source code is just about unreadable, being made up mostly of #defines for all the functions.

bench mark - Relatively permanent material object, natural or artificial, bearing a marked point whose elevation above or below an adopted datum is known.

map hypsographic Map showing relief with elevations referred to the national geodetic vertical datum of 1929. map, hypsometric Map showing relief by any convention, such as contours, hachures, shading, or tinting.

BenchmarkA brass or bronze disk set in a concrete base or other permanent structure, inscribed with a mark showing its elevation above or below an adopted vertical datum.

cartographic representative of the surface of the Earth or a subsurface feature through a series of three-dimensional coordinate values: a continuous variable over a two-dimensional surface by a regular array of z values referenced to a common datum.

An estimate of the earth's surface based on an ellipsoid provides a determination of the elevation of every point on the earth's surface, including sea level, and is often called a datum.

A digital representation of a continuous variable over a two-dimensional surface by a regular array of z values referenced to a common datum. Digital elevation models are typically used to represent terrain relief.

There is another critical bit of information that is required before you are totally confused: the datum. The need for a datum is the consequence of man's inability to describe mathematically the exact shape of the earth.

This function supports most geodetic datum used around the world. This function can convert the control points or be applied to a single point.
For 3D VRML export, the output file now includes color and image draping information.

Geodetic Datums (Dana/Geographer's Craft) -- Introduction to geodetic datums; Figure of the earth: geometric models, reference ellipsoids, global coordinate systems, earth surfaces; Geodetic datums.

This conversion requires both a transformation between ellipsoids and a datum shift. Numerous datums have been used for mapping around the world. For details, see Snyder (1987; 1989).

The software performs transformation on raster and vector data sometimes of differing datums, grid system, or reference system, into one coherent image. It can also analyse changes over time within a region.

All parametric equipment types include at least one nozzle manager datum.
Vertical vessel with legs (TANK_V4LEG) correctly orients legs straddling the axis of the vessel.
Label tool selects individual equipment nozzles.

Both 32661 and 4326 use the WGS 84 datum and ellipsoid but one is long lat (4326) and one is a meter based one. The WGS 84 simply defines the ellipse and datum.

But the earth's mountains bump-up and valleys bump-down from the ellipsoid so a datum is designed to fit the earth's surface that accounts for the actual wrinkling of the globe as established by orbiting satellites.

Take a look at the projection definition you copied (Imported) for the la_to_ny shapefile you created with ArcToolbox, what Spheroid was used with the Datum?
3b. Briefly state what the difference between Spheroid and Datum is.
3c.

Geodetic Datum Overview, Department of Geography, University of Colorado at Boulder
Global Positioning System Overview, Department of Geography, University of Colorado at Boulder ...

Geodetic Datums Overview
The Mercator Conformal Projection Norris Wiemer, University of Alberta.
John Snyder An obituary of the man who achieved immortality by computerizing the mathematical algorithms for transforming map projections.

Attributes (see description above);
Geographic information describing the position of the datum in space relative to other data; and
Temporal information describing the instant or period of time for which the datum is valid.

This should at least include dataset names with descriptions of what they contain, coordinate system & datum, theoretical accuracy, source document names with dates & scales, data conversion methods, update history, ...

The data related to a particular part of the Earth surface are often in different format, have different georeferencing (datum heterogeneity, projection heterogeneity, etc.), end different resolution.

Data editing
Data manipulation
Edge-matching
Datum conversions, transformations, and projections
Topology building
Data structuring
Attaching data attributes to graphics
Data format conversions ...

altitude -- elevation above or below a reference datum, as defined in Federal Information Processing Standard 70-1. See also elevation.

A reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid. A geographic coordinate system definition includes a datum, prime meridian, and angular unit.
Layer1 ...

The 'srid' column is one of the most important because it stores the 'Spatial Reference Indentifier' value which dictates the projection and datum to be used to correctly display the geographic data on the surface of the earth.

These include data layer classifications, source media and digitizing standards, datums, projections, coordinate systems, cartographic elements, and output scales.

NAD - North American Datum: The official reference ellipsoid used for the primary geodetic network in North America.
Node: The beginning and ending locations of a line on a digital map.

ArcInfo supports these transformations: similarity, affine, piecewise linear, projective, NADCON datum adjustment using minimum-derived curvature transformation, and a polynomial transformation to warp grids and images.

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

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