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A map projection produced by the direct projection of the points of the ellipsoid (used to represent the earth) by straight lines drawn through them from some given point. The projection is usually made upon a plane tangent to the ellipsoid at the end of the diameter joining the point of projection and the center of the ellipsoid. The plane of projection is usually tangent to the ellipsoid at the center of the area being mapped. he analytical expressions that determine the elements of the projection. If the point of projection is at the center of the ellipsoid, a gnomonic map projection results; if it is at the point opposite the plane’s point of tangency a stereographic map projection; and if at infinity (the projecting lines being parallel to each other), an orthographic map projection. Most map projections are not perspective. Also called GEOMETRIC MAP PROJECTION.

Related Terms

BALANCED RUDDER

A rudder design where the pivot point and the center of its area meet, reducing the effort needed to turn it.

It has about 20% of the rudder area forward of the rudder axis.

CENTRE OF BUOYANCY

The center of the area of the underwater transverse or longitudinal section of a hull at a particular trim, hence the point at which the force of buoyancy is regarded to be acting vertically upwards.

PNEUMATIC CONTROL VALVE

A valve in which the force of compressed air against a diaphragm is opposed by the force of a spring to control the area of the opening for a fluid stream.

PLASMA-ARC CUTTING

Metal cutting by melting a localized area with an arc followed by removal of metal by high-velocity, high-temperature ionized gas.

PLAN EQUATION

The mathematical statement that horsepower plan/33,000, where p mean effective pressure (pounds per square inch), l length of piston stroke (feet), a net area of piston (square inches), and n number of cycles completed per minute.

PISTON GAGE SEE FREE-PISTON GAGE. PISTON METER

A variable-area, constanthead fluid-flow meter in which the position of the piston, moved by the buoyant force of the liquid, indicates the flow rate. Also known as piston-type area meter.

PICTURE ELEMENT

1. That portion, in facsimile, of the subject copy which is seen by the scanner at any instant; it can be considered a square area having dimensions equal to the width of the scanning line. 2. In television, any segment of a scanning line, the dimension of which along the line is exactly equal to the nominal line width; the area which is being explored at any instant in the scanning process. Also known as critical area; elemental area; pixel; recording spot; scanning spot.

PARISON SWELL

In blow molding, the ratio of the cross-sectional area of the pariso

PACKING DENSITY

The number of devices or gates per unit area of an integrated circuit. packing ring See piston ring.

OVERRUN

A cleared area extending beyond the end of a runway.

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