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Topic: Geographic datum

	Geodetic Datum Overview
		Geodetic datums define the size and shape of the earth and the origin and orientation of the coordinate systems used to map the earth.
		Datums have evolved from those describing a spherical earth to ellipsoidal models derived from years of satellite measurements.
		The diversity of datums in use today and the technological advancements that have made possible global positioning measurements with sub-meter accuracies requires careful datum selection and careful conversion between coordinates in different datums.
	www.colorado.edu /geography/gcraft/notes/datum/datum.html (1532 words)

	Coming to Terms
		The origin of this datum is a point on the earth referred to as Meades Ranch in Kansas.
		The origin for this datum is the earth's center of mass rather than the point on the earth (as with NAD27), which causes the locations of previous control points in North America to shift, sometimes as much as 500 feet.
		NADCON is the fastest, simplest, and most accurate datum transformation for mapping at scales of 1:200 and smaller and is intended for conversion of NAD27 to NAD 83 in the continental United States, Puerto Rico, and the Virgin Islands.
	www.esri.com /news/arcuser/0401/terms.html (803 words)

	Geographic coordinate system - Wikipedia, the free encyclopedia
		A geographic coordinate system expresses every location on Earth by two of the three coordinates of a spherical coordinate system which is aligned with the spin axis of Earth.
		Borrowing from theories of ancient Babylonians, later expanded by the famous Greek thinker and geographer Ptolemy, a full circle is assigned 360 degrees (360°).
		For example, data in latitude/longitude with the datum as the North American Datum of 1983 is denoted by 'GCS_North_American_1983'.
	en.wikipedia.org /wiki/Geographic_coordinate (709 words)

	Geographic Calculator
		The Geographic Calculator supports map files in AutoCAD DWG and DXF (R2000 or earlier), MapInfo MIF and TAB (the native MapInfo format), and ESRI Shapefile (the native ArcView format) formats.
		As with the NADCON method the shift values for a geographic area are stored in a set of grid files, one representing latitude shifts (named with the extension.las) and one representing longitude shifts (named with the extension.los).
		The shift values for a geographic area are stored in a set of grid files, one representing latitude shifts (named with the extension.las) and one representing longitude shifts (named with the extension.los).
	www.bluemarblegeo.com /products/calculator.php?op=faq (1567 words)

	Maine DEP GIS
		Geographers have long used coordinate systems, for example both DaVinci and Mercator developed their own systems in the 1500s, and sailors relied heavily on early maps and coordinate systems to navigate the seas.
		Geographic (latitude/longitude) is the most commonly-used coordinate system, but typically it is not used as a GIS coordinate system because it lacks a consistent unit of measurement.
		Geographic is useful as a tool for global locating, but it cannot perform calculations such as area and length because a degree varies in size based on latitude (a degree of longitude at the equator is approximately 110 miles, at 45
	www.maine.gov /dep/gis/training/gdc/coordinate_systems.shtml (751 words)

	Standardization of Coordinate Systems and Datums for Data Exchange
		Datum Shift: In West Virginia the difference in the coordinates between the NAD 1983 and NAD 1927 Datums is approximately 20 meters for geographic coordinates, 200 meters for UTM coordinates, and as much as 6 miles for State Plane coordinates.
		A geodetic datum consists of a set of three dimensional (3D) coordinate axes (x,y,z), whose origin is within a few hundred meters of the center of mass of the Earth, and a reference ellipsoid that is an ellipsoid of revolution.
		Defining a datum consists of (1) specifying the origin and orientation of the datum's coordinate axes relative to the Earth and (2) specifying the the size and shape of the reference ellipsoid to be used.
	wvgis.wvu.edu /otherdocs/standardsandpubs/wv_coordinate_systems_aug02.html (4392 words)

	FM 6-2 Chptr 11 Conversion and Transformation
		The computation of conversion from UTM coordinates to geographic coordinates is performed on DA Form 5601-R (Computation--Conversion of UTM Coordinates to Geographic Coordinates (BUCS)) by using the BUCS.
		A datum is any numerical or geometrical set of quantities specifying the reference coordinate system used for geodetic control in the calculation of coordinates of points on the earth.
		Datums may be either global or local in extent.
	www.globalsecurity.org /military/library/policy/army/fm/6-2/ch112.htm (2872 words)

	Datum (Site not responding. Last check: )
		Datum transformations using Molodensky equations (implemented in most geo-software) are becoming increasingly important, because of the growing use of GPS data...
		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...
		Datum - a mathematical reference framework for geodetic coordinates defined by the latitude and longitude of an initial point, the azimuth of a line from this point, and the parameters of the ellipsoid upon which the initial point is located...
	gisfigyelo.geocentrum.hu /lexikon/datum_en.html (440 words)

	Project 1 (Site not responding. Last check: )
		Geographic coordinates (also nick-named geos) is the geographic coordinate system (the graticule are laid over the sphere) that allows us to determine location based on a predetermined central meridian and central parallel.
		In this case NAD27 uses the Clark 1866 ellipsoid (an ellipsoid that is centered on the U.S.A.), and the NAD83 uses GRS 80 ellipsoid (an ellipsoid that is centered on the Earth's center of mass, and which is also very similar to the WGS84 ellipsoid).
		Geographic coordinate graticule are laid over an ellipsoid, while UTM and SPCS are both plane coordinate systems that are where the graticule are laid on a flat surface and are georeferenced.
	www.personal.psu.edu /sya108/proj1.html (790 words)

	Geoscience Australia: Geodesy - Datums and Coordinates (Site not responding. Last check: )
		A Vertical Datum is used to fix a position in the vertical direction, up and down the Z axis.
		Australia's vertical datum is the Australian Height Datum [AHD] which approximates mean sea level and was determined by monitoring tide gauges around the Australian coastline.
		A horizontal datum is used to fix a position in the X and Y directions.
	www.ga.gov.au /nmd/geodesy/datums/aboutdatums.jsp (2554 words)

	Geographic Coordinate System Transformations (Site not responding. Last check: )
		The transformations may be most readily achieved by first expressing the observed or source geographical coordinates in terms of three dimensional XYZ cartesian values (geocentric coordinates) instead of the normal angular expressions of latitude and longitude.
		In the early days of satellite surveying when relationships between datums were not well defined and the data itself was not very precise, it was usual to apply merely a three parameter dX, dY, dZ shift to the XYZ coordinate set in one datum to derive those in the second datum.
		It is also possible to interpolate geographical or grid shifts for points on the basis of known shifts for a number of control points in a specific defined area.
	www.posc.org /Epicentre.2_2/DataModel/ExamplesofUsage/eu_cs35.html (5780 words)

	GIS Tips
		And while there, they used telescopes, pendulums, gravity meters, or whatever it is that those folks use (they’re called geodesists), to determine the latitude and longitude of a single point, and the true azimuth to another point.
		Before long, a whole network of known points, all referenced to the original datum were established which could be used by surveyors all over the country to perform their tasks.
		The development of a datum is a labor intensive and expensive proposition, so the development of a new datum is almost always based on the work, carefully documented as described above, of any previously existing datum.
	www.mentorsoftwareinc.com /CC/gistips/tips0698.htm (619 words)

	SailNet Articles (Site not responding. Last check: )
		The difference between the datum of the chart and the datum selected in your GPS unit can have a significant impact on navigational accuracy.
		The problem is that not all datum is the same and unless you're aware of the different datum, you could get a wrong reading of where your are.
		Geographic datum is a frame of reference used by cartographers to define a chart's grid of coordinates.
	www.sailnet.com /collections/articles/index.cfm?articleid=sexton012 (636 words)

	Geographic coordinate system
		A datum is a set of values that defines the position of the spheroid relative to the center of the earth.
		Whenever you change the datum, the geographic coordinate system is altered and the coordinate values will change.
		For example, the coordinates in DMS of a control point in Redlands, California using the North American Datum of 1983 (NAD 1983) are: "-117 12 57.75961 34 01 43.77884" The coordinates of the same point on the North American Datum of 1927 (NAD 1927) are: "-117 12 54.61539 34 01 43.72995".
	publib.boulder.ibm.com /infocenter/db2luw/v8/topic/com.ibm.db2.udb.doc/opt/csb3022a.htm (941 words)

	[No title]
		The Geographic Calculator converts individual coordinates, point databases, and map files from virtually any coordinate system, datum, and map projection to any other.
		The accuracy and speed of the Geographic Calculator have allowed us to move forward quickly with building the Bahamian NSDI and the technical support provided by Blue Marble has been outstanding in working through EPSG tables and other items.
		Geographic Calculator gives me the ability to quickly and efficiently explore different combinations of alignments.
	www.bluemarblegeo.com /products/calculator.php?print=1 (2982 words)

	Dictionary
		Geographic coordinates and attributes can be transferred from one address to the other.
		Datum: A set of parameters and control points used to accurately define the three-dimensional shape of the Earth (e.g., as a spheroid).
		Typically involves the assembly of a very small geographic portion of the overall project area but the maximum range of data types and procedures anticipated in the development and operation of the ultimate geographic data model.
	www.kam.to /kam/services/gisdictionary.cfm (10034 words)

	Maine DEP GIS
		Geographers have long used coordinate systems, for example both DaVinci and Mercator developed their own systems in the 1500s, and sailors relied heavily on early maps and coordinate systems to navigate the seas.
		Geographic (latitude/longitude) is the most commonly-used coordinate system, but typically it is not used as a GIS coordinate system because it lacks a consistent unit of measurement.
		Geographic is useful as a tool for global locating, but it cannot perform calculations such as area and length because a degree varies in size based on latitude (a degree of longitude at the equator is approximately 110 miles, at 45
	www.state.me.us /dep/gis/training/gdc/coordinate_systems.shtml (751 words)

	Reference Datum
		A reference datum is a known and constant surface which can be used to describe the location of unknown points.
		An example of a datum that could be used for the earth is a sphere with a radius equal to the average radius of the earth.
		By using an oblate ellipsoid as a datum for the earth we have a shape that approximates the shape of the earth fairly well and provides a datum to which points all over the earth's surface can be referenced (hence the term 'reference datum').
	geology.isu.edu /geostac/Field_Exercise/topomaps/ref_datum.htm (388 words)

	New Page 0
		As with geodetic datums, the parameters required to define a vertical datum can vary and can be complex, but for practical geographical information processing whilst the definition of the vertical datum may be useful it is not essential.
		Geographic 3D and geocentric co-ordinates in one co-ordinate system can be transformed to another geodetic co-ordinate system if the relative positions of the two systems can be described.
		The parameters are commonly referred to defining the datum transformation "from Datum 'A' to Datum 'B'", whereby (X, Y, Z) are the geocentric co-ordinates of the point on Datum ´A ´ and (X ´, Y ´, Z´) are the geocentric co-ordinates of the point on Datum ´B´.
	www.databydesign.co.uk /energy/ukdata/coord.htm (12244 words)

	Geographic Translator 1.0/Geographic Transformer 3.0 (Site not responding. Last check: )
		The problem, of course, was that two different datums were used: The GPS produced latitude and longitude using the World Geodetic System datum, and the USGS map used the North American Datum of 1927 (NAD27), the precursor to the North American Datum of 1983 (NAD83).
		Geographic Transformer performs the same feat, but for images such as scanned maps, photographs and satellite data.
		The user must enter information on the input coordinates and datum, the output coordinates and datum, output cell resolution and the area of the input map to be translated.
	www.geoplace.com /gw/1997/0597/0597qt1.asp (1344 words)

	Working with Datasets
		The geographic datum used in recording, WGS84, unless otherwise specified in the file.
		The geographic data file contains the cluster ID that corresponds to the cluster ID in each of the survey datasets (individual woman, child, births, etc.).
		Because of the sensitive nature of geographic datasets and a few other restricted datasets, an additional form must be filled out for these specific datasets before access can be granted.
	www.measuredhs.com /help/Datasets/Working_with_datasets.htm (958 words)

	GeoMagnetic Calculator
		The Geographic Magnetic Calculator is a tool to help you determine UTM Coordinates and the Magnetic Declination that correspond to a longitude/latitude location.
		For all USGS topographical maps, the default Datum is the NAD CONUS 1927.
		The newer WGS 84 datum can be selected, or 18 other datums.
	www.resurgentsoftware.com /geomag.html (271 words)

	krijg: datum in correct opname verslagen
		A datum is something used as a basis for calculating and measuring.
		On standard principles of modern English usage, the correct plural of datum is 'datums' and a Google search reveals 158 000 occurrences of this term.
		A datum is when surveyors all get together and agree to be wrong.
	www.longyangclub.nl /datum_in_correct_opname_verslagen.html (292 words)

	[GRASS5] Fixing up projection related code...
		It needs to be PROJ.4.4.6 or later as the earlier versions had some bugs in the datum transformations.
		The library containing the GRASS proj wrapper functions is now called libgproj instead of libproj, again so as not to conflict with the external version.
		Frank said he didn't see this as an attribute of the datum, but of the co-ordinate system, so I have left it for now.
	grass.itc.it /pipermail/grass5/2003-April/007587.html (807 words)

	[No title]
		All material must be critically examined, with particular attention directed to the actual date of the survey, geographic datum, depth unit, plane of reference, purpose and quality of the survey, and whether it is an original source or from another compilation.
		Sounding datums used in coastal areas for nautical charting are determined by local observations, ideally over a period of 19 years.
		Finally, coastline is a line of ordinary low water along that portion of the coast which is in direct contact with the open sea and the line marking the seaward limit of inland waters.
	historicals.ncd.noaa.gov /cm_preview.txt (1011 words)

	geographic_coordinate_system
		The longitude of a point is specified as an angle between the local meridian of the point and the chosen reference meridian, measured in the equatorial plane.
		The height is the distance between a point and a vertical datum, such as the ellipsoidal surface associated with the geodetic datum.
		geodetic_datum M geodetic_datum This is the geodetic datum that this geographic coordinate system is based upon.
	www.august.com /epicentre/inherit/geographic_coordinate_system.html (533 words)

	Doc Savage's Archaeology Downloads (Site not responding. Last check: )
		Geographic coordinate systems measure the Earth in terms of latitude (degrees north or south of the equator), and longitude (degrees east or west of a prime meridian).
		Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across its two dimensions (that is, on paper).
		However, this is also somewhat of a problem, because unprojecting the data results in a coordinate system in decimal degrees, which is meaningless for measuring distance and area (since a degree of longitude is greatest at the equator, and is zero at the poles).
	archaeology.asu.edu /jordan/Reproject.html (3424 words)

	NGA: (U) GEOTRANS 2.4 Geographic Translator (UNCLASSIFIED)
		GEOTRANS (Geographic Translator) is an application program which allows you to easily convert geographic coordinates among a wide variety of coordinate systems, map projections, and datums.
		To convert a set of coordinates, simply select the coordinate system or map projection, and the datum, in which your coordinates are defined, enter the source coordinates, select the coordinate system or map projection, and the datum, to which you want the coordinates to be converted, and click on the Convert button.
		Using the GEOTRANS file processing interface, you can select an existing file of coordinates to be converted, define the coordinate system or map projection, and the datum, to which you want to convert the coordinates, and specify the name and location of the output file that is to be created.
	earth-info.nga.mil /GandG/geotrans (682 words)

	Knowledge Base - GIS Technical Support
		Then geographic coordinate systems (GCS) were devised, which include a datum, units of measure, and a prime meridian.
		The underlying datum and spheroid to which coordinates for a dataset are projected can change the coordinate values.
		It is necessary to specify a geographic or datum transformation when using the ArcToolbox Project Wizard to project shapefiles and geodatabase feature classes between different geographic coordinate systems, or datums.
	gis.sfsu.edu /helpdesk/arcmap/projections.htm (1974 words)

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