koobee.wublee@gmail.com wrote:

> On Feb 23, 12:01 pm, Eric Gisse wrote:
> 
>>On Feb 23, 9:49 am, koobee.wub...@gmail.com wrote:
> 
> 
>>>You need four satellites where each satellite should know its time and
>>>position.  Time can just be a counter with all the satellites
>>>synchronized to within a count of each other.  Each satellite then
>>>just broadcast its time and position information as almanac signal to
>>>whoever wants to receive it.
>>
>>>Since the distance is traveled by light with a known speed, you can
>>>then easily form a set of four equations with four unknowns.  The four
>>>unknowns are your time (relative to the counter in each satellite) and
>>>position.
>>
>>>**  c^2 (t1 – t)^2 = (x1 – x)^2 + (y1 – y)^2 + (z1 – z)^2
>>>**  c^2 (t2 – t)^2 = (x2 – x)^2 + (y2 – y)^2 + (z2 – z)^2
>>>**  c^2 (t3 – t)^2 = (x3 – x)^2 + (y3 – y)^2 + (z3 – z)^2
>>>**  c^2 (t4 – t)^2 = (x4 – x)^2 + (y4 – y)^2 + (z4 – z)^2
>>
>>>Where
>>
>>>**  (t1, x1, y1, z1) = Time and position of satellite 1
>>>**  (t2, x2, y2, z2) = Time and position of satellite 2
>>>**  (t3, x3, y3, z3) = Time and position of satellite 3
>>>**  (t4, x4, y4, z4) = Time and position of satellite 4
>>>**  (t, x, y, z) = Time and position of the receiver
>>
>>>Notice that relativistic effect is never needed.
>>
>>...even tnough t1-4 are wrong by roughly 50,000ns/day?
> 
> 
> So, the college drop-out sleeps until 11AM Alaska time today.
> 
> In the meantime, if t1 is off by 50usec a day relative to the ground,
> as long as t2, t3, and t4 are all off by the same amount, it does not
> matter.  There is still no need for any relativistic correction.
> <shrug>
> 
> 
Of course the relativitistic correction is needed. The satellites
get their location information from the ground. They need to know
the times for that.  Read about how the gps works.