Fette, in Cognitive Radio Technology (Second Edition), 2009 Signal Processing of GPS Signals The height is the distance from the nearest point normal on the assumed altitude.
The longitude is then found by rotating around the y-axis until the x-axis coincides with the vector from the center of the earth to the position. The latitude is found by rotating around the z-axis until the x-axis crosses the projection from the position on to the x–y-plane.
The system takes its basis in the ECEF rectangular frame. This system expresses position in latitude, longitude and height, and is given in the spherical coordinates. The other representation is called ECEF geodetic frame. Its x-axis points through the intersection of the prime median (0° longitude) and equator (0° latitude), its z-axis towards the true North Pole (parallel to the earth’s rotational axes), and the y-axis to complete the right hand rule through the intersection of 90° longitude and equator ( Fig. 11.3). This is named the ECEF rectangular system but is usually just referred to as the ECEF system. The first representation frame gives its position in Cartesian coordinates, based on its distance from the center according to each axis. Of all the possible combinations of ECEF coordinate systems, two are of particular importance. This frame has its center in the center of the earth, and the frame is stationary relative to the surface. The earth centered-earth fixed (ECEF) frame is mostly used in the case of global-positioning based navigation. Baudoin, in Using Robots in Hazardous Environments, 2011 Earth centered-earth fixed frame The position of any point on the earth's surface is given uniquely by the intersection of the circles of latitude and longitude.īy convention, the latitude is given first when giving the position of any point.S.A. Global positioning satellite systems and radar have added to the tools available to the modern navigator. The advent of radio in the early twentieth century enabled navigators to verify the accuracy of their chronometers with time signals broadcast from known locations. It took until the 1850's to build accurate chronometers cheap enough for their widespread use.
The second, and simpler, method involved taking a chronometer, which could keep very accurate time at sea, and calculate position almost immediately by comparing the chronometer time for the fixed reference point with local time. This method required the compilation of tables of reference values (an almanac) for every day of every year well in advance of their required use - a task which required a lot of human calculating time in a pre-electronic computer era. One involved measuring the lunar distance - the angle between the Moon and another celestial object (a star or the sun) - which would lead to determination of the position of the measurer through calculation based on reference values. If a navigator knew the time at a particular fixed reference point when the local time could be determined at the ship's location, the difference between the reference time and the apparent local time would give the ship's position relative to the fixed location. These values vary from $$ per hour, so there is a direct relationship between time and longitude. Content Latitude and Longitude Latitude Latitude is a measure of the position of a point on the earth's surface in terms of degrees north or south of a baseline - the equator.
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