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22 Cards in this Set
- Front
- Back
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What happens with coordinates in earthquakes?
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Ellipsoid remains the same; coordinates of a landmark can be slightly shifted.
Solution: Resurvey and update them. |
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What longitudes do the North and South poles have?
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none / 0° / all longitudes
(Mathematical Poles are different to the Magnetic Poles) |
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Why do we need ellipsoids?
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Earth is flattened at the poles because the earth rotates
An ellipsoid is the best mathematical approximation of the earth. |
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Why can there be so many different definitions for ellipsoids?
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Since earth is not completely flat, every region has its own ellipsoid, so distortions can be minimized.
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What is the essence of a datum?
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A datum gives information about fixing a coordinate system to an object (in this case the Earth). It uses physical marks to define origin, orientation and size of the coordinate system. With a datum, a coordinate system is turned into a coordinate reference system. It can also consist of coordinate sets (= realization).
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What is a geodetic datum?
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A mechanism through which the relationship between ellipsoid and geoid is defined.
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Is the geoid the “true” shape of the earth?
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No. Geoid is that equipotential surface which most closely corresponds to mean sea level.
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What is the main difference between ellipsoid and geoid?
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Ellipsoid = mathematical model
Geoid = physical model |
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What is the difference between reference system and datum?
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A datum uses physical landmarks to fix a coordinate system to an object.
Then points can be measured in a reference system. |
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WGS84 vs. ITRF?
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Different realizations:
WGS84 (= World Geodetic System 1984): monitor stations of GPS ITRF (= International Terrestrial Reference Frame): other stations |
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How would you establish a reference system for the moon?
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Z-axis is the mean axis of rotation and the x-axis is the intersection of the Equator and the
Prime Meridian. The x-axis is normal to the z-axis through the origin of the system, which is the Moon’s center of mass. The y-axis is orthogonal to the x- and z-axes. |
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How would you establish a reference system for the moon? 2
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To establish a reference system for the moon I would choose right-handed spherical coordinates where the z-axis is the mean axis of rotation and the x-axis is the intersection of the Equator and the Prime Meridian. The x-axis is normal to the z-axis through the origin of the system, which is the Moon’s center of mass. The y-axis is orthogonal to the x- and z-axes. Latitude is the angle between a line extending from the origin to the planetary equator and a vector from the origin to the point of interest. Longitude is the angle between this vector and the plane of the Prime Meridian measured in an eastern direction.
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Spheroid vs. ellipsoid?
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Spheroid = similar to a sphere
Ellipsoid = rotation of an ellipse |
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Can one measure the ellipsoid?
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No. It’s just a mathematical model
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Transformations vs. Conversions?
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Transformation = change of datum
Conversions = no change of datum |
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What is a graticule?
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A lattice of parallels and meridians.
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What are geographic / geodetic coordinates?
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Latitude, Longitude, (Ellipsoidal) Height
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What are geocentric coordinates?
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X, Y, Z
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What are projected coordinates?
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E, N
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How can datums be classified?
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Geodetic, Vertical, Engineering, Image Datum
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What is a compound coordinate system?
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A Combination of two independent coordinate systems: one for horizontal, one for vertical position
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What is EPSG?
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European Petroleum Survey Group
Provides codes and parameters for reference systems. |
