GPS - A difference between "satellites in view" "satellites in use"?

Author

A difference between "satellites in view" "satellites in use"?

Hugh Janus

2007-09-21, 4:33 am

Hi all,

Is there a difference between "satellites in view" "satellites in
use"? When reading the NMEA output from GPS receiver I was being told
that I had 9 satellites in view. But a different sentence was telling
me that I was using 3 satellites. Is this normal or is there a
difference between these values or is my GPS going nuts?

Thanks

Darren Griffin - PocketGPSWorld.Com

2007-09-21, 4:33 am

On 2007-09-21 09:44:08 +0100, Hugh Janus <my-junk-account@hotmail.com> said:

> Hi all,
>
> Is there a difference between "satellites in view" "satellites in
> use"? When reading the NMEA output from GPS receiver I was being told
> that I had 9 satellites in view. But a different sentence was telling
> me that I was using 3 satellites. Is this normal or is there a
> difference between these values or is my GPS going nuts?
>
> Thanks

Put simply, though 'In View' the signal from some SV's may be below the
threshold for useful position data.
--
Darren Griffin
PocketGPSWorld - www.PocketGPSWorld.com
The Premier GPS Resource for News, Reviews and Forums

2007-09-21, 7:33 am

On Fri, 21 Sep 2007 10:14:33 +0100, Darren Griffin - PocketGPSWorld. Com
wrote:
>
> Put simply, though 'In View' the signal from some SV's may be below the
> threshold for useful position data.

I thought this was an example of the Garmin satellite status page, when
some are initially shown with a hollow signal bar, which after a while
goes solid: They're all in view, but only the solidly-barred ones are
usable; the hollow bars indicates that the receiver's "collecting data"
(which takes, IIRC, ~30s once the satellite's appeared) in order to make
those satellites usable.

A.

Larry G

2007-09-21, 10:33 am

On Sep 21, 5:36 am, "A" <a...@nospam.com> wrote:
> On Fri, 21 Sep 2007 10:14:33 +0100, Darren Griffin - PocketGPSWorld. Com
> wrote:
>
>
>
> I thought this was an example of the Garmin satellite status page, when
> some are initially shown with a hollow signal bar, which after a while
> goes solid: They're all in view, but only the solidly-barred ones are
> usable; the hollow bars indicates that the receiver's "collecting data"
> (which takes, IIRC, ~30s once the satellite's appeared) in order to make
> those satellites usable.
>
> A.

I think ...."in view" means that the satellites are in a sky position
where they _should" be viewable....

But the GPS cannot know if there are obstructions... like canyons,
buildings or even tree cover....

So... basically I think it shows the birds is "should" be able to
see... and then the solid bars show the one's it actually has acquired
and is using...

thoughts?

Sam Wormley

2007-09-21, 12:33 pm

Hugh Janus wrote:
> Hi all,
>
> Is there a difference between "satellites in view" "satellites in
> use"? When reading the NMEA output from GPS receiver I was being told
> that I had 9 satellites in view. But a different sentence was telling
> me that I was using 3 satellites. Is this normal or is there a
> difference between these values or is my GPS going nuts?
>
> Thanks
>

Certainly there is a difference... NMEA output is telling you
that only three of nine satellites were being used in the PVT
solution at that instant. Reasons might include

o obstruction
o satellite off line
o ephemeris not acquired
o receiver often does not use satellites with poor
signal-to-noise or other parameter constraints

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