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Topic: Gnomonic projection

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Map projection

Azimuthal equidistant projection

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	MAP PROJECTION. The Columbia Encyclopedia: Sixth Edition. 2000 (Site not responding. Last check: 2007-10-20)
		Some projections preserve correct relative distances in all directions from the center of the map (equidistant projection); some show areas equal to (equal-area projection) or shapes similar to (conformal projection) those on a globe of the same scale; some are useful in determining direction.
		In all cylindrical projections the meridians of longitude, which on the globe converge at the poles, are parallel to one another; in the Mercator projection the parallels of latitude, which on the globe are equal distances apart, are drawn with increasing separation as their distance from the equator increases in order to preserve shapes.
		The point light source may be located at the globe’s center (gnomonic projection), on the globe’s surface directly opposite the tangent point (stereographic projection), or at some other point along the line defined by the tangent point and the center of the globe, e.g., at a point infinitely distant (orthographic projection).
	www.bartleby.com /aol/65/ma/mapproje.html (851 words)

	Map - Printer-friendly - MSN Encarta
		Geometric projections are classified according to the type of surface on which the map is assumed to be developed, such as cylinders, cones, or planes; plane projections are also known as azimuthal or zenithal projections.
		Although the shapes of areas on the cylindrical projection are increasingly distorted towards the poles, the size relationship of areas on the map is equivalent to the size relationship of areas on the globe.
		The gnomonic projection is assumed to be formed by rays projected from the centre of the Earth.
	uk.encarta.msn.com /text_761577953___26/Map.html (1144 words)

	Projection - definition from Biology-Online.org
		Conical projection, a mode of representing the sphere, the spherical surface being projected upon the surface of a cone tangent to the sphere, the point of sight being at the center of the sphere.
		Cylindric projection, a mode of representing the sphere, the spherical surface being projected upon the surface of a cylinder touching the sphere, the point of sight being at the center of the sphere.
		polar projection, a projection of the sphere in which the point of sight is at the center, and the plane of projection passes through one of the polar circles.
	www.biology-online.org /dictionary/Projection (308 words)

	Azimuthal Map Projections
		The gnomonic projection is a perspective projection with the light source located at the centre of the generating globe.
		The stereographic projection is a conformal projection and is commonly used for maps of the polar region.
		The orthographic projection assumes that the light source is an infinite distance from the point of tangency, resulting in the rays of light being parallel to each other and perpendicular to the projection surface.
	www.fes.uwaterloo.ca /crs/geog165/azproj.htm (753 words)

	Cylindrical Map Projections
		Cylindrical stereographic projections are rarely used, although Gall's stereographic projection has been proposed as compromise projection having less distortion of distances than the cylindrical gnomonic projection and less distortion of shapes than the cylindrical orthographic projection.
		On this projection, parallels of latitude are equally spaced along meridians, the distance between parallels being equal to the arc length between parallels on the generating globe.
		Distortion on this projection is minimal at the intersection of the central meridian and the Equator and generally increases with distance from this point.
	www.fes.uwaterloo.ca /crs/geog165/cylproj.htm (1163 words)

	page
		The plane of projection is represented by a straight line drawn from point A to point G such that the segment AG is parallel to BC (or the equator).
		Projections of latitudes are drawn by extending a straight line from the light source to the projection plane at the same angular distance from the equator possessed by the latitude.
		The radii of such concentric circles used to draw the projected parallels is equivalent to the radius of the circle * tan (90° - angular distance of latitude).
	www.math.ubc.ca /~cass/courses/m309-01a/ting/page.html (671 words)

	Azimuthal Projections
		The stereographic projection is a true perspective projection with the globe being projected onto the UV plane from the point P on the globe diametrically opposite to the point of tangency.
		The gnomonic projection is the perspective, azimuthal projection with point of perspective at the center of the globe.
		The default clipping region for the gnomonic projection is a circle with a radius of 60 degrees at the center of projection.
	idlastro.gsfc.nasa.gov /idl_html_help/Azimuthal_Projections.html (999 words)

	Gnomonic (Site not responding. Last check: 2007-10-20)
		An azimuthal projection that is a perspective projection and is neither conformal nor equal-area.
		Except at the center, distortion of shape, area and scale on the Gnomonic projection is so great that it has seldom been used for atlas maps.
		Several sets of star maps from the late 18th century and some terrestrial maps of 1803 used this projection with the sphere projected onto the six faces of a tangent cube.
	www.manifold.net /doc/700/gnomonic.htm (165 words)

	Map Projections Poster
		For example, the basic Mercator projection is unique; it yields the only map on which a straight line drawn anywhere within its bounds shows a particular type of direction, but distances and areas are grossly distorted near the map's polar regions.
		Some projections are suited for mapping large areas that are mainly north-south in extent, others for large areas that are mainly east-west in extent, and still others for large areas that are oblique to the Equator.
		Cylindrical— Mathematically projected on a cylinder tangent to the Equator.
	erg.usgs.gov /isb/pubs/MapProjections/projections.html (3465 words)

	azimuth.html
		The gnomonic projection is a perspective view of the globe as seen by an observer at its center.
		The stereographic projection is a perspective view of the globe from a point on the surface that lies on the far side from the reference point.
		The red line is the equal area projection, the blue is the gnomonic, the green is for the equidistant, fl represents the stereographic and yellow the orthographic.
	people.clarkson.edu /~chengweb/faculty/taylor/maps/azimuth1.html (1296 words)

	Gnomonic Projection \| International Meteor Organization (Site not responding. Last check: 2007-10-20)
		P is the center of the projection, and thus the center of the chart.
		The meteor's projection on the map is the intersection between the plane determined by the great circle and the plane of the stellar map.
		Gnomonic projection is not true to area or angle.
	www.imo.net /visual/minor/gnomic (436 words)

	Aquariu.NET Documentation
		The orthographic projection assumes that the light source is an infinite distance from the projection surface, resulting in parallel rays of light.
		Stereographic projections are rarely used, although Gall's stereographic projection has been proposed as compromise projection having less distortion of distances than the cylindrical gnomonic projection and less distortion of shapes than the cylindrical orthographic projection.
		The Equator is shown as true to scale on the map, and as is typical of cylindrical projections, there is a narrow band along the Equator in which distortion of all geometric characteristics is minimal.
	www.mgaqua.net /AquaDoc/Projections/Projections_Azimuthal.aspx (536 words)

	Overview of Map Projections -- 3DSoftware.com (Site not responding. Last check: 2007-10-20)
		A conic projection can be visualized as placing a cone over the Earth, with the cone's peak (apex) along the polar axis of the Earth, and the cone's surface touching the Earth along a constant latitiude.
		The stereographic projection is used to map polar regions, and large continent-sized areas that extend similarly in all directions.
		The Gnomonic Projection is projected from the center of the Earth.
	www.3dsoftware.com /Cartography/USGS/MapProjections/Overview (1108 words)

	About TerraServer-USA
		Because of the curvature of the globe, the parallels of latitude nearest the poles when projected onto the cylinder are spaced progressively closer together, and the projected meridians of longitude are represented as parallel straight lines, perpendicular to the equator and continuing to the North and South poles.
		The gnomonic projection is assumed to be formed by rays projected from the center of the earth.
		Because the source of the gnomonic projection is at the center of the earth, all great circles, that is, the equator, all meridians, and any other circles that divide the globe into two equal parts, are represented as straight lines.
	terraserver.microsoft.com /About/AboutGlossaryProj.htm (1123 words)

	Gnomonic Projections
		The gnomonic projection has been around for at least 2,500 years -- the ancient Greeks are credited with using this projection to map stars.
		Tearing: Gnomonic maps tend to have rounded edges, and are typically used to cover areas the size of continents.
		Mathematically, a gnomonic projection could be used to map just less than half the Earth (i.e., just less than a single hemisphere), but the amount of distortion along the edges of a gnomonic map that large would be enormous.
	www.cnr.colostate.edu /class_info/nr502/lg2/projection_descriptions/gnomonic.html (539 words)

	Spherical Projections
		We project the point through the center of the sphere and plot it, using some symbol or label to denote that the point is on the other side of the sphere.
		We project the point orthographically toward the plane onto the other side of the sphere and plot it, again using some symbol or label to denote that the point is on the other side of the sphere.
		Because all the projections are azimuthal, the azimuth of the projected point from (X = 0, Y = 0) is always the same as the azimuth on the sphere from (l = 0, w = 0).
	www.uwgb.edu /dutchs/structge/sphproj.htm (1580 words)

	5.3.5 Gnomonic Projection (-Jf -JF)
		The Gnomonic azimuthal projection is a perspective projection from the center onto a plane tangent to the surface.
		The projection is neither equal-area nor conformal, and much distortion is introducted near the edge of the hemisphere; in fact, less than a hemisphere may be shown around a given center.
		Scale as 1:xxxxx or as radius/latitude where radius is distance on map in inches from projection center to a particular [possibly oblique] latitude (-Jf), or map width (-JF).
	www.ucalgary.ca /appinst/pubdoc/gmt344/doc/html/GMT_Docs/node55.html (182 words)

	SkyView User's Guide (Site not responding. Last check: 2007-10-20)
		The Gnomonic projection is an infinite projection in that all points on the plane can be mapped onto the sphere (though the reverse is not true).
		The Gnomonic projection also has the characteristic that all great circles are mapped as straight lines, hence the shortest distance between two points is a straight line.
		The gnomonic projection is called a tangent projection in some of the astronomical literature and gnomonic projections are specified in FITS files with the suffix -TAN on the CTYPE keywords.
	skyview.gsfc.nasa.gov /help/skyuser.html (6357 words)

	Map Projections
		Map projections are often viewed as a mathematical operation in which coordinates X,Y are written as a pair of parametric functions of latitude
		Polyconic projections are performed by projecting points on the surface of the earth onto a series of frustums of cones that are fitted together.
		A map projection on a cylinder tangent to the earth at the equator.
	www.bae.uky.edu /~precag/BAE599/Module_1/Notes/projections.html (485 words)

	The Gnomonic Projection (Site not responding. Last check: 2007-10-20)
		The Gnomonic projection is one which has a greater expansion, away from the origin, than a conformal projection.
		It is constructed by projecting every point on the globe appearing in the map onto the plane of the map from an imagined light source in the center of the globe.
		Hence, on the gnomonic projection, all great circles are represented by straight lines, making it very useful in plotting great circle routes between arbitrary destinations.
	members.shaw.ca /quadibloc/maps/maz0201.htm (177 words)

	Coordinate Projections Used for IRAS Maps
		The projection cylinder is tangent to the celestial sphere at the Galactic equator and the projection proceeds by projecting radially outward from each point on the polar axis of the Galactic coordinate system in a plane parallel to the equatorial plane.
		The gnomonic projection produces a geometric projection of the celestial sphere onto a tangent plane from a center of projection at the center of the sphere.
		The orthographic projection, like the gnomonic projection, is a projection of the celestial sphere onto a tangent plane, but the center of projection is infinitely distant from the tangent plane.
	irsa.ipac.caltech.edu /IRASdocs/surveys/coordproj.html (1067 words)

	NOOBEED - Projection Class Function Manual (SET)
		This projection is used only in the spherical form, hence the radius of the sphere will be taken from the value of the semi-major axis of the defined ellipsoid.
		It is the perspective projection of the globe from the center onto a plane tangent to the surface.
		This projection is used only in the spherical form, hence the radius of the sphere will be taken from the value of the semi-major axis of the defined ellipsoid.All angles are required and expressed in degrees.
	noobeed.com /nb_projection_manual_set.htm (2001 words)

	5.3.4 Azimuthal Equidistant Projection (-Je -JE)
		Therefore, a circle about the projection center defines the locus of points that are equally far away from the plot origin.
		The projection, in the polar aspect, is at least several centuries old.
		It is a useful projection for a global view of locations at various or identical distance from a given point (the map center).
	www.earth.rochester.edu /ees254/gmt/doc/html/GMT_Docs/node54.html (189 words)

	[No title] (Site not responding. Last check: 2007-10-20)
		The Gnomonic projection (Figure 9-2) is another member of the azimuthal projection family (maps projected to a plane surface that is tangent to the globe at a single point), and it has the distinction of being the only map projection on which any straight line represents a great-circle arc.
		Figure 9-2, for example, shows a Gnomonic projection centered on the North Pole and extending outward only 65° (to 25° N latitude), and it is evident how distorted the shapes have become.
		To achieve a straight line for the great-circle arc between Miami and Tokyo with this projection, one could rotate the projection to a position where Miami and Tokyo lie on the "equator" of the projection, much as was done along the central meridian in Figure 9-3.
	www.gis.psu.edu /projection/chapter9.html (1057 words)

	ESA - Cassini-Huygens - First full mosaics of Titan’s surface
		One particular kind of projection used for spheres in two dimensions (for example on some maps of Earth or the celestial sphere) is ‘stereographic’ projection.
		A ‘gnomonic’ projection has also been produced, and this tends to make the surface appear as if it was flat.
		This type of projection is often found on maps used by navigators and aviators in determining the shortest distance between two points.
	www.esa.int /SPECIALS/Cassini-Huygens/SEMWTY5TI8E_0.html (711 words)

	Conic Projection (Site not responding. Last check: 2007-10-20)
		To grasp the concept of conic projection, again imagine the earth as a glass sphere with a light at the center.
		conic projection, the cone is cut and flattened out to form the map or chart, whereas the gnomonic projection will appear as is. On the conic projection, points lying close together on either side of the meridian along which the cone is cut will be widely separated on the map.
		On this projection the meridians are parallel, and the parallels are parallel to each other and perpendicular to the meridians; therefore, the direction of north or east is the same anywhere on the map.
	www.tpub.com /inteng/9i.htm (562 words)

	CineSat Projections
		The projection plane intersects the earth at a given standard parallel (including the special case of a tangent plane in the North or South pole).
		The LAZIMUTH projection is a generalization of the ETAP (equivalent transverse azimutal) projection of previous releases.
		Cylindrical projections map the earth onto a cylinder which either touches the globe along the equator or intersects it at a given standard parallel.
	www.cinesat.com /csprj.htm (1684 words)

	Azimuthal Projections
		Hence, with the gnomonic projection, the interior of a hemispherical region of the globe is projected to the
		The region on the globe that is mapped lies between 20 degrees and 70 degrees of latitude and -130 degrees and -70 degrees of longitude.
		Gamma is the angle, expressed in degrees clockwise from north, of the rotation of the projection plane.
	hesperia.gsfc.nasa.gov /~jma/idl_html_help/projections9.html (1384 words)

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