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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' can be applied to the practical problem of describing positions of features on or near the earth' ...

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.

Geodetic Datum - WGS 84 - NAD 83 - GPS
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Google Maps - Latitude and Longitude ...

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. On other planets, such as the Moon or Mars, the datum is the average radius of the planet.

The Geocentric Datum of Australia (GDA) is the new Australian coordinate system, replacing the Australian Geodetic Datum (AGD). GDA is part of a global coordinate reference frame and is directly compatible with the Global Positioning System (GPS).

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. Datums are reference surfaces that consider the curvature of the earth for the mathematical reduction of geodetic and cartographic data.
GEOID ...

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.

Datum
A datum is a mathematical surface on which a mapping and coordinate system is based.
Digital elevation model (DEM)
A topographic surface arranged in a data file as a set of regularly spaced x, y, z coordinates where z represents elevation.

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

Datums
Datums are sets of parameters and ground control points defining local coordinate systems. Because the earth is not a perfect sphere, but is somewhat "egg-shaped," geodesists use spheroids and ellipsoids to model the 3-dimensional shape of the earth.

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. There are many different datums and hence many different starting positions.

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.
Digital Elevation Model (DEM) ...

A datum is a system which allows the location of latitudes and longitudes (and heights) to be identified onto the surface of the Earth - ie onto the surface of a 'round' object.
The basic mathematical/geometric principle which is used is that: ...

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.

Datums (sets of data) are the basis for all geodetic survey work. They act as reference points in the same way that starting points do when you give someone directions.

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. The "+towgs84" parameter can be used to define either 3 or 7 term datum transform coefficients, satisfying this requirement.

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).
Combination of parameters and control points used to accurately define the three dimensional shape of the Earth (spheroid).

Datum
A reference point or surface against which position measurements are made, and an associated model of the shape of the earth for computing positions.

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). See also Ellipsoid and Mean sea level.
...

Datum transformation support: SDO_COORD_OPS, SDO_COORD_OP_METHODS, SDO_COORD_OP_PARAM_USE, SDO_COORD_OP_PARAM_VALS, SDO_COORD_OP_PARAMS, SDO_COORD_OP_PATHS, SDO_PREFERRED_OPS_SYSTEM, SDO_PREFERRED_OPS_USER ...

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.
National Spatial Data Infrastructure ...

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. If you link to or cite these materials, please credit the author, Peter H.

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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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. The North American Datum of 1983 is based on the modern GRS 1980 ellipsoid - almost identical to the most widely used WGS 1984 ellipsoid which is also geocentric.

Geodetic Datum
A math model representing the size and shape of the earth (or a portion of it).

(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, orientation and scale of the coordinate system and ties it to the earth, ...

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. 220 difference between two bands (near infrared minus visible red) divided by the sum of the two bands; high values indicate active vegetation growth; often applied to NOAA AVHRR data.

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.DatumIn geomatics, a mathematical model used to approximate the size and shape of the earth.

digital elevation model The digital 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. Over time, and in different countries, many datums have been developed and used.

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. This is a common GIS product created at a variety of scales.

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. This software is central to the professional analysis and presentation of GIS data.

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.

Z-score The (signed) number of standard deviations an observation or datum is above or below the mean. A positive standard score represents a datum above the mean, while a negative standard score represents a datum below the mean.

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
Coordinate Systems 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.

altitude -- elevation above or below a reference datum, as defined in Federal Information Processing Standard 70-1. See also elevation.
area -- a generic term for a bounded, continuous, two-dimensional object that may or may not include its boundary.

Wide range of Map Projections and Datums supported
Non-destructive, parameter based image chains
Native file access
Precision Terrain correction and ortho-rectification
Advanced Mosaicing, compositing and fusions
Elevation support
Vector and shapelib support ...

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.

HOW WE KNOW WHERE SOMETHING IS First, a disclaimer: This text does not pretend to cover issues such as geodetic datums, projections, coordinate systems, and other terms from the fields of geodesy and surveying.

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, lists of field names & what they contain, ...

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.

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

With names like State Plane, UTM, Albers and many others, projections can be quite thorny for novice GIS users (compounded by a related factor, called a 'datum' which defines the surface of the earth as of a certain date).

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. Standards and guidelines for these aspects of GIS are scheduled for development within WGIAC's GIS Standards Plan document.

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. A node is topologically linked to all lines that meet at the node.

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, Information, Coordinate, Geographic, Location

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