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POLYCONIC  PROJECTION - 14070_195
QUESTIONS - 14070_197

Engineering Aid 1 - Advanced Structural engineering guide book
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Figure  9-25.-Lambert  conformal  conic  projection. chart  projection.  A  great  circle  is  any  line  on  the earth’s  surface  (not  necessarily  a  meridian  or  the equator) that lies in a plane that passes through the earth’s center. Any meridian lies in such a plane; so does  the  equator.  But  any  parallel  other  than  the equator lies in a plane that does not pass through the earth’s center; therefore, no parallel other than the equator is a great circle. Now, 1 minute of arc measured  along  a  great circle is equal to 1 nautical mile (6076.115 ft) on the ground. But 1 minute of arc measured along a small circle  amounts  to  less  than  1  nautical  mile  on  the ground.   Therefore,   a   minute   of   latitude   always represents a nautical mile on the ground, the reason being that latitude is measured along a meridian and every meridian is a great circle. A minute of longitude at the equator represents a nautical mile on the ground because, in this case, the longitude is measured along the equator, the only parallel that is a great circle. But a minute of longitude in any other latitude represents less than a nautical mile on the ground; and the higher the latitude, the greater the discrepancy. LAMBERT CONFORMAL CONIC PROJECTION The  Lambert   conformal   conic   projection attains such a near approach to both directional and distance conformality as to justify its being called a conformal   projection.   It   is   conic,   rather   than polyconic,  because  only  a  single  cone  is  used,  as shown  in  figure  9-25.  Instead  of  being  considered tangent to the earth’s surface, however, the cone is considered  as  penetrating  the  earth  along  one standard  parallel  and  emerging  along  another. Direction is the same at any point on the map, and the distance scale at a particular point is the same in all Figure 9-26.-distortion of the Lambert conformal conic projection with the standard parallels at 29 degrees and 45 degrees. 9-22







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