To describe the position of an object, there must be a related coordinate system. The location of the GPS receiver on the surface of the earth is relative to the earth. Therefore, to describe the position of the GPS receiver, the coordinate system that is solid on the earth, the coordinate system that is rotated with the earth, the earth coordinate system as the reference system.

　　There are two types of geometric expression on the earth coordinate system, namely the earth's right -angle coordinate system and the earth's land coordinate system. The definition of the Earth's right -angle coordinate system is: the original point O coincides with the earth's quality, the Z axis points to the Earth's Arctic, the X -axis points to the intersection of the Earth equatorial surface and the Greenwitzer's lunch circle (that is, the direction of 0 longitude), and the Y axis is in the equatorial plane with XOZ The right -handed coordinate system (that is, the direction of 90 degrees in the east). The definition of the earth's coordinate system is that the center of the ellipsoid of the earth is overlapped with the earth's quality, and the short shaft of the ellipsoid is overlapped with the Earth's rotation axis. The earth latitude at any point on the earth is the angle of the ellipsoid method line and the ellipsoid equatorial surface of this point. The height H of this point is the distance from the point of the point to the ellipsoida. Any point P is set on the earth surface, P (x, Y, Z) is expressed in the right -angle coordinate system of the earth, and the expression of the earth coordinate system on the earth is P (φ, λ, H). The interchange relationship between the two is: the earth coordinate system becomes a right -angle coordinate system: (1) In the formula: n is the radius radius of the cypherical circle of ellipsoids, E is the first chips of the ellipsoid. If the long radius of the ellipsoid is A and the short radius is B, there are (2) right -angle coordinate system becomes the earth coordinate system.

　　The initial value φ = φc is set for stacking until | φi = 1-φi | less than a certain limits.

　　These two coordinate systems are often used in the positioning system, and they must be familiar with the conversion relationship between the two coordinate systems.

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