NORMAL LINE—A line that is parallel to twoplanes of projection and perpendicular to thethird. A line or plane that forms a 900 angle withanother line or plane is normal to that line orplane.NORTHING—One of the two values indicatingthe position of a point on a grid system. Thenorthing coordinate is abbreviated N. (See GRIDCOORDINATES.)OBLIQUE PROJECTION—A single view of anobject showing three dimensions (length, width,and height).OBLONG—A nonequilateral rectangle.OBTUSE ANGLE—An angle greater than 90°.OCCUPIED STATION—A traverse or triangu-lation station over which a theodolite or anengineer transit is set up for the measurement ofangles at this station. Also, a station at whichangles have been so measured.OCTAGON—A polygon of eight sides.OFFSET LINE—A supplementary line close to,and usually parallel to, a main survey line to whichit is referenced by measured offsets. When the linefor which data are desired is in such a positionthat it is difficult to measure over it, the requireddata are obtained by running an offset line in aconvenient location and measuring offsets fromit to salient points on the other line.OGEE CURVE—Any curve composed of twoconsecutive tangent circular arcs that curve inopposite directions; also known as reverse curve.OPEN TRAVERSE—A traverse that starts at apoint of known or assumed position and ends ata point whose relative position is unknown withrespect to the starting point.ORDER OF ACCURACY—A mathematicalratio defining the general accuracy of themeasurements made in a survey. The orders ofaccuracy for surveys are divided into four classesnamed first-order, second-order, third-order, andfourth-order.ORGANIC SOIL—Soil that contains mineralgrains and a more or less conspicuous admixtureof vegetable matter.ORIENT—To establish the correct relationshipin direction with reference to the points of thecompass; to bring into correct relationship indirection with reference to the points of thecompass.ORTHOGRAPHIC PROJECTION—The pro-jection of height, width, and depth of an objectinto various single planes so as to depict the truesize and shape of the object as seen from eachindividual plane, each plane showing only twodimensions, thereby necessitating a minimum oftwo planes to show all three dimensions.PARALLAX—The apparent displacement or thedifference in apparent direction of an object asseen from two different points not on a straightline with the object. In testing the focus of atelescope, the head of the observer must movefrom side to side or up and down while sightingthrough the eyepiece. Any apparent movement ofthe cross hairs in relation to the object imagemeans that parallax is present. Parallax can bepractically eliminated by careful focusing.PARALLEL OF LATITUDE—A line on thesurface of the earth having the same latitude atevery point.PARALLELEPIPED—A solid figure whose baseis a parallelogram.PARALLELOGRAM—A quadrilateral with eachpair of opposite sides parallel.PARTIAL AUXILIARY VIEW—An auxiliaryview in which only the features of an object thatare specifically desired are shown.PARTIAL SECTION—A sectional view con-sisting of less than a half section; used to showthe internal structure of a small portion of anobject; also known as a broken section.PAVEMENT STRUCTURE—All courses ofselected material placed on the foundation orsubgrade soil, other than any layers or coursesconstructed in grading operations.PENTAGON—A polygon of five sides.PERCENT—Portion in one hundred parts.PERIMETER—The sum of the sides of apolygon.AI-10
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