Projection of a point on a plane
(gcide) | Projection \Pro*jec"tion\, n. [L. projectio: cf. F. projection.]
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1. The act of throwing or shooting forward.
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2. A jutting out; also, a part jutting out, as of a building;
an extension beyond something else.
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3. The act of scheming or planning; also, that which is
planned; contrivance; design; plan. --Davenant.
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4. (Persp.) The representation of something; delineation;
plan; especially, the representation of any object on a
perspective plane, or such a delineation as would result
were the chief points of the object thrown forward upon
the plane, each in the direction of a line drawn through
it from a given point of sight, or central point; as, the
projection of a sphere. The several kinds of projection
differ according to the assumed point of sight and plane
of projection in each.
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5. (Geog.) Any method of representing the surface of the
earth upon a plane.
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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.
Globular, Gnomonic, Orthographic, projection,etc. See
under Globular, Gnomonic, etc.
Mercator's projection, a mode of representing the sphere in
which the meridians are drawn parallel to each other, and
the parallels of latitude are straight lines whose
distance from each other increases with their distance
from the equator, so that at all places the degrees of
latitude and longitude have to each other the same ratio
as on the sphere itself.
Oblique projection, a projection made by parallel lines
drawn from every point of a figure and meeting the plane
of projection obliquely.
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.
Powder of projection (Alchemy.), a certain powder cast into
a crucible or other vessel containing prepared metal or
other matter which is to be thereby transmuted into gold.
Projection of a point on a plane (Descriptive Geom.), the
foot of a perpendicular to the plane drawn through the
point.
Projection of a straight line of a plane, the straight line
of the plane connecting the feet of the perpendiculars let
fall from the extremities of the given line.
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Syn: See Protuberance.
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