Almighty001

Almighty001, you have created some nice looking and colorful figures for the section, Position calculation introduction. With regard to "Two spheres intersecting in a circle", I removed some of the language in the text which is no longer appropriate with your new figure.

With regard to the figure, "Surface of a sphere intersection a circle (i.e. the edge of a disk) at two points", I think this colorful figure has advantages over the wire mesh type figure that I was using. However, I think it should be drawn a little differently. The smaller inset figure should be removed. The two points of intersection should be shown on the main figure at the two points where the circle meets the sphere. Please consider revising this figure. Your contributions are appreciated. RHB100 (talk) 20:30, 8 October 2008 (UTC)

Basic concept of GPS

Hi!

There are two different issues with the introduction. The first is style - this is supposed to be a very easy-to-read introduction. The description as intersecting spheres is covered in much detail later in the article. Since the article is already very long, perhaps another description is not needed in the introduction.

The second issue is the number of satellites needed. This is 3 with an accurate clock (a ns or so will suffice). This gives the distance to 3 satellites, which is enough to determine position. (These will be 2 solutions, but only one can be close to the surface of the Earth, so this is not a practical problem.) With 4 satellites you need only a crude clock, provided your hardware measures the 4 satellites at (almost) the same time. This allows you to solve for x,y,z, and t. See any GPS textbook for the details of how this is done. LouScheffer (talk) 18:57, 5 November 2008 (UTC)