09-GEODETIC-&-CONTROL-SURVEYS Flashcards
- Which of the following statements correctly describes the origin of the North American Datum (NAD) of 1927?
A. The origin of NAD27 is at Meades Ranch in Kansas.
B. The origin of NAD27 is geocentric.
C. The geodial height if the origin of NAD27 is assumed to be zero.
D. Both A and C are true.
D. Both A and C are true
Solution: The origin is located at Meades Ranch in Kansas, and the azimuth from Meades Ranch to Waldo is defined as 75°28’09.64”. The geodial height is assumed to be zero, and NAD27 is not geocentric.
- Which of the following statements correctly describes the North American Datum of 1983?
A. The origin of NAD 83 is geocentric.
B. NAD 83 is the horizontal control datum used throughout the western hemisphere.
C. Coordinates based on NAD 83 have replaced those based on NAD 27 throughout the US.
D. Both A and B are true.
A. The origin of NAD83 is geocentric
Solution: NAD83 is based on the geocentric origin. 250,000 points, including 600 stations whose positions had been determined by satellite geodesy, were used to constrain the datum to the geocentric origin.
- NAD83 uses a figure to represent the earth that closely approximates its shapes, but may be described mathematically by a few definite parameters. What is the shape?
A. a biaxial ellipsoid rotated about its minor axis
B. a mean earth ellipsoid
C. a biaxial ellipsoid rotated about its major axis
D. a triaxial ellipsoid
A. a biaxial ellipsoid rotated about its minor axis.
Solution: The shape of the earth is represented in NAD83 by an ellipsoid of revolution that is biaxial and rotated about its minor axis. The actual shape of the earth is oblate, that is flattened at the poles. Rotation approximates the shape.
- Which of the following statements correctly characterizes the transformation of coordinates from NAD27 to NAD83?
A. There is not one simple, consistent method to reliably transform from NAD27 to NAD83.
B. The transformations of ellipsoidal coordinates can be accurately accomplished with a simple, one step math formula, but Cartesian coordinates cannot.
C. The transformation of Cartesian coordinates from NAD27 to NAD83 can be accurately accomplished with a simple, one-step math formula, but ellipsoidal coordinates cannot.
D. The transformation from state plane coordinates expressed in NAD27 to NAD83 involves a change in the origin of the coordinates.
A. There is not one simple, consistent method to reliably transform from NAD27 to NAD83.
Solution: The most reliable transformations are based on a return to the original observations and the performance of a readjustment of the entire region.
- What is the geoid?
A. The geoid is a surface defined by earth’s gravity.
B. The geoid is a surface that is flattened without tearing or stretching.
C. The geoid is a surface that would closely resemble the ocean’s surfaces if they were completely still.
D. Both A and C are true
D. Both A and C are true
Solution: One way to understand the geoid is to imagine that trenches have been cut through the land masses of the earth, and water has been allowed to flow into them. The surface assumed by the water would then approximate the surface known as the geoid.
- What is the cause of geodial undulation?
A. The pressure of magnetically attractive ores within the earth cause the geoid to undulate.
B. The center of mass of the earth does not coincide with the center of the geoid.
C. The ellipsoid is not coincident with the geoid.
D. The mass of the earth is irregularly distributed and, therefore the geoid is also irregular.
D. The mass of the earth is irregularly distributed and, therefore the geoid is also irregular.
Solution: The geoid is defined by earth’s gravity. The unequal distribution of the mass of the earth causes irregularity in the force and direction of gravity consequently, the geoid is also irregular.
- What is the vertical datum most often used in the U.S.?
A. The U.S. Standard Datum
B. the IGL Datum
C. the NAP Datum
D. The National Geodetic Vertical Datum of 1929
D. The National Geodetic Vertical Datum of 1929
Solution: The datum was based on observed heights of mean sea level at 26 tidal stations, 21 in the U.S. and 5 in Canada, and the Atlantic, Gulf, and Pacific Coasts. Additionally, more that 100,00km of leveling established benchmarks throughout the U.S.
- In considering surveys of a very large extent, can a level surface at mean sea level be considered parallel with a level surface 100.0m above mean sea level?
A. No, a level surface is perpendicular everywhere to the direction of gravity.
B. Yes, every level surface is parallel to every other level surface.
C. No, level surfaces that are 100.0m apart at the equator would be approximately 99.5m apart at the poles, so the cannot be considered parallel.
D. Both A and C are true.
D. Both A and C are true.
Solution: While level surfaces may be considered parallel for surveying a limited area, in fact they are not. The geoid, a close representation of a level surface, is not only discontinuous over variations of density in the earth, but is subject to ta general convergence as well. The relative distance between two level surfaces will decrease from the equator to the poles as a consequence of the increase in gravity.
- Which of the following best defines map projection?
A. the systematic transformation of the state plane coordinates into Cartesian coordinates.
B. the rigorous mathematical transference of points on a spheroid to the points on a plane surface.
C. the function of relating an ellipsoid of revolution the the geoid.
D. the mathematical development of the graticule representing the geographical lines on a globe.
B. the rigorous mathematical transference of points on a spheroid to the points on a plane surface.
Solution: The earth is curved, and maps are flat. If the graticule, or grid, of a map is to correspond with the parallels of latitude and meridians of longitude on the terrestrial surface, and the orderly method of transference must be adopted. There are many map projections that accomplish this, each has unique characteristics.
- Which of the following map projections is used as the basis of state plane coordinate systems in the U.S.
A. the Lambert projection
B. the oblique transverse Mercator projection.
C. the transverse Mercator projection.
D. A. B and C
D. A. B and C
Solution: The Lambert projection and the transverse Mercator projections form the foundation of nearly all of the state plane coordinates systems. However, Zone 1 of the Alaska system is based on an oblique transverse Mercator projection.
- Which of the following best describes a developable surfaces?
A. a portion of the earth’s surface that corresponds to mean sea level.
B. a polar gnomonic map projection
C. a plane figure upon which the information from a spheroid may be projected and then flattened without gross distortion or tearing.
D. a surface that a map of a portion of the earth’s surface may be drawn upon without any direction.
C. a plane figure upon which the information from a spheroid may be projected and then flattened without gross distortion or tearing.
Solution: The difficulty of representing the earth’s surface on a flat map can be solved by projecting the information from an ellipsoidal representing of the earth onto some surface that may be unrolled or developed, such as a cone or cylinder. These conic sections (if a cylinder may be so considered) can each be cut along an element and neatly flattened, minimizing distortion. Distortion can never be completely eliminated, however.
- What characteristic of a map projection preserves the shape of small figures from the ellipsoid to that map.
A. Propagation
B. Standardization
C. Spatiality
D. Confomality
D. Confomality
Solution: Some map projections allow for the angles between two curves on the spheroidal surface to be preserved on the map. This property, known as conformality, provides for the maintenance of elementary shapes on the map.
- Which of the following curves appears as a straight line on a gnomonic map projection?
A. the parallels of latitude
B. rhumbs lines
C. the arcs of great circles.
D. the arcs of small circles.
C. the arcs of great circles.
Solution: The arc of a great circle will be a straight line on a gnomonic map projection, which is generated on a plane tangent to the ellipsoid of a at a single point.
- Which of the following terms may be correctly applied to the Lambert map project that is used as the foundation for state plane coordinates in the U.S.?
A. conformal and conic
B. azimuthal and equal-area
C. cylindrical and conformal
D. conic and sinusodial
A. conformal and conic
Solution: Conformal is the characteristic of the Lambert projection that preserves the shape of small figures as they are transformed form the ellipsoid to the mapping plane. The Lambert projection is a conic projection; that is, the developable surface employed is imagined to be a cone.
