Spheroid
A spheroid is an ellipsoid having two axes of equal length, making it a surface of revolution.
Spheroid
The true shape of the earth, the geoid, can be averaged out to form a more regular, mathematical shape -- the spheroid, a sort of three-dimensional oval shape.
Spheroidal Heights
Global positioning, such as GPS, will generally give a latitude, longitude (or x and y position) and height. This height is usually the height above (or below) the Spheroid (Ellipsoid).
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.
spheroid The earth is more or less round. The exact nature of the "more or less" can have significant effects on how well the absolute position of features can be represented on a map.
spheroid
A three-dimensional shape obtained by rotating an ellipse about its minor axis, resulting in an oblate spheroid, or about its major axis, resulting in a prolate spheroid.
Spheroid - The standard globe that is obtained by projecting the ellipsoid on to a regular surface closer to the shape of a sphere. The spheroid is used as the model for the determination of common spherical coordinates of latitudes and longitudes.
3. Spheroid or ellipsoid of rotation
Reference: Ellipsoid of rotation (Maling 1973, p. 2)
this is the figure created by rotating an ellipse about its minor axis ...
The spheroid shown is the ArcView "sphere."
On a map there will be two points M1 and M2 corresponding to P1 and P2, respectively.
The thick blue line still shows the geodesic.
Oblate Spheroid
It was Charles Darwin who first suggested that the earth was not a true sphere but, due to centrifugal force created by rotation, had expanded perpendicular to the axis of rotation.
Spheres, spheroids and geoids
Geoid, from the Greek for "Earth-shaped", is the common definition of our world's shape. This recursive description is necessary because no simple geometric shape matches the Earth: ...
oolite Spheroidal grains of sand size, usually composed of calcite and thought to have formed by inorganic precipitation.
open pit mining Surficial mining, in which the valuable rock is exposed by removal of overlying rock or soil.
3. Projection, Spheroid, Geodetic datum, Levelling datum, notes relating to the basis geodetic data ...
Sphere;
> Oblate spheroid (disk-shaped);
< Prolate spheroid (cigar-shaped);
>> Scalene ellipsoid ("three unequal sides").
Spatial Error--The spheroid and projection errors as they relate to precision are particularly important to mention for BADL.
as a spheroid). The datum is the basis for a planar coordinate system. For example, the North American Datum for 1983 (NAD83) is the datum for map projections and coordinates within the United States and throughout North America.
slope map See: map, slope soil map See: map, soil spheroid Mathematical figure closely approaching the geoid in form and size and used as a surface of reference for geodetic surveys.
Spheroidal Weathering A type of below ground chemical weathering where the corners of jointed rocks become rounded over time. Rock changes from a rectangular to more round shape.
This type of figure is termed an oblate ellipsoid or spheroid, and is the three-dimensional shape obtained by rotating an ellipse about its shorter axis.
A datum defines the position of that spheroid relative to the center of the earth. The datum determines the placement of the coordinate system upon the ellipsoid.
Projection consists of two main stages: first the surface of the earth is estimated through the use of a geometric description called an ellipsoid (sometimes, though not always correctly, referred to as a spheroid), ...
The Challenge: The Earth is a spheroid, and the best way to represent it is with a globe.
The Mercator projection can be visualized as a spheroid projected onto a cylinder tangent to the equator and parallel to the polar axis (Figure 4-2). When the cylinder is opened and flattened, a distortion appears.
Latitude and longitude are two of the three polar coordinates needed to describe a sphere (or spheroid) precisely (the third being r, the distance of the earth's surface from the center of the earth.), ...
Horizontal Datum: The two most common spheroidal reference surfaces in Canada used as a reference or base to accurately define horizontal positions (x,y or longitude, latitude) are the North American Datum of 1927 (NAD27) or the more recent and ...
A coordinate system is usually defined by a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y-directions to locate x,y positions of point, line, ...
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.
In fact, measurements have shown that Earth's gross shape is not a true spheroid, i.e., all points on the surface are not equidistant from the geometric center.
See Also: ellipsoid, prolate ellipsoid, spheroid
[mathematics] An ellipsoid created by rotating an ellipse around its minor axis. The shape of the earth approximates an oblate ellipsoid with a flattening ratio of 1 to 298.257.
A datum is a set of accurately surveyed horizontal control points that define the shape of the Earth as a spheroid and form the basis for a 2-dimensional coordinate system.
as a spheroid). The corresponding datum is the basis for a planar coordinate system. For example, the North American Datum for 1983 (NAD83) is the datum for map projections and coordinates within the United States and throughout North America.
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.
LATITUDE
The angular distance north or south between a point on the Earth's surface and the Equator. The distance is measured with reference to an idealised, spheroid-shape of the Earth.
Their southern routes gives a shorter degree than Picard, the son goes on to measure a northern route and finds this degree is longer. He propose a prolate spheroid as the correct shape for the earth.
If your projection is UTM, and the focus is not in North America, then your earth model is probably the World Geodetic Spheroid of 1972 or WGS 1984. These guesses will cover about 95 percent of the data encounterd at the GSD.
However, a 2D hexagon shape (beehive honey comb) abuts completely without gaps in planimetric space (termed "fully nested"); as does a combination of pentagon and hexagon shapes nests to form the surface of a spheroid (soccer ball).
Map projections Map projections are a method of representing information from a curved surface (usually a spheroid) in two dimensions, typically to allow indexing through cartesian coordinates.
 See also: Surface, Coordinate, Map, Area, Geographic
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