الاخوة والاخوات
قمت بدراسة موضوع طريقة عمل النظام العالمي لتحديد المواقع
http://www.nasm.si.edu/exhibitions/gps/work.html
Determining Position
A GPS receiver "knows" the location of the satellites, because that information is included in satellite transmissions. By estimating how far away a satellite is, the receiver also "knows" it is located somewhere on the surface of an imaginary sphere centered at the satellite. It then determines the sizes of several spheres, one for each satellite. The receiver is located where these spheres intersect.
Click here for a detailed description of how this works.
اي أنه على الاقل نحتاج الى 3 اقمار صناعية كي نحدد الموقع لم افهم كيف؟؟

في الموقع كتب بالانجليزية التالي:
Although the distance to the satellites can only be roughly estimated at first, a GPS receiver can precisely calculate these distances relative to each other. Because the relative size of the spheres is known, there is only one possible point where they can intersect.





In this diagram, the solid lines indicate
where the GPS receiver "thinks" the spheres
are located. Because of errors in the
receiver's internal clock, these spheres do
not intersect at one point.




The GPS receiver must change the size of the spheres until the intersection point is determined. The relative size of each sphere has already been calculated, so if the size of one sphere is changed, the other spheres must be adjusted by exactly the same amount.
Three spheres are necessary to find position in two dimensions, four are needed in three dimensions.

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