Re: Garmin nuvi Antenna Question

peter wrote:

We are talking about two related but different things.

In n-dimensional space, n points are needed to get the triangulation:

- With the coordinates of one point and a fixed radius, you get a
sphere.
- The second point defines the intersection of two spheres, which is
hopefully a circle.
- The third coordinate reduces the system to two points and after
ignoring one of them (*) for not being on earth's surface the location
is determined.

That's the theory. Now, the practice.

All the Garmin GPS units that I have had however, will report having
acquired the satellites and start operating only after five of them are
detected.

-Ramon

(*) True story: one day, a scientist solving an equation for mass chose
not to ignore the extra negative result from a square root. Any
physicist would have ignored it, but not Albert Einstein, and that's
how he discovered matter with negative mass, a.k.a. anti-matter.

Ramon F Herrera wrote:

Nope, the above would be the theory *if* the receiver had an accurate
(i.e. synchronized atomic) clock. Since it doesn't you don't actually
know the radius of the circle when you get the first satellite
reception and when you get two satellites you only know the difference
between the two radii, not their actual values.

The result is that you need reception of at least four satellite
signals to get a 3D position plus the accurate time.


Don't know which particular models you have, but all the Garmin's that
I've used (45XL, III+, II+, eMap, V, assorted eTrexi, 60CSX) have
agreed with the threory and report a 2D position shortly after getting
a lock on 3 satellite signals and a 3D position when they lock onto a
4th. The rare exceptions have been on occasions when the satellite
geometry has been poor such as having all the initially received sats
in an almost straight line in which case an additional satellite or two
were needed.


Two problems with the above being a true story. Antimatter has
positive mass (but opposite charges from normal matter), and it was
first proposed by Wehl and Dirac based on Dirac's relativistic quantum
mechanics equations, not Einstein.

Garmin now offers an "automotive mount" for the Nuvi series. It
includes a detachable base that's compatible with their ubiquitous
"bean bag". Mine works beautifully, is moveable and uses the same bean
bag I've used for years with my GPS-V. It eliminates any need for
suction cups and/or adhesive disks.

http://shop.garmin.com/accessory.jsp?sku=010%2D10815%2D01


pete

peter wrote:


I only buy the top of the line at the time they are introduced:

- StreetPilot 2610
- StreetPilot 2620
- StreetPilot 2730
- n=FCvi 660

I am currently using the last two concurrently.

-Ramon

Ramon F Herrera wrote:

If they really will consistently not navigate when only 4 satellites
can be received then there's either a design flaw or your particular
unit is defective. Contact Garmin and let them know of the problem.