GPS/GLONASS/GALILEO/BAIDOU - How important?

[MattS]

I knew someone would do it for me (seriously I am playing around with something else at the moment - very unsuccessfully!).

The Humminbird antenna is internal, situated on the starboard side of the wheelhouse; the Onwa antenna is external just about a foot to port. Both antenna are very close in line fore and aft. So 1.24 ft is pretty good but I would expected it more 2.5ft apart. The Onwa was using 24 sats, the Hummin only 8. There also is a different of opinion of the two transducers: Onwa says there was 3.645m of water while the Humminbird quoth 3.492m of water. Variation of 0.153m. Onwa ducer port side, Humminbird has ducer's both side but the depth reads off the starboard. The boat was on the mooring in line with the stream and the variation is the slope of creek (I claim!).

There is a third antenna which is on the centre line and has pitch, elevation and roll correction but I didn't note the lat/long at the time.

Ta Matt

Of course the inaccuracy of the fix can be in the direction of reducing the gap between the two coordinates as well ?

 

[Buck Turgidson]

If your receiver is any good it will give you an accuracy value sometimes known as an EPU. Estimated of position uncertainty. This is the radius around the declared position where you could be. If your receiver is SBAS enabled ( EGNOS in Europe) you can expect sub 5m accuracy 95% of the time. There isn’t much or any benefit to having multiple system reception as the constellations are full and you are unlikely to have fewer than 5 satellites in view unless you are surrounded by high terrain in which case GPS isn’t your optimal nav aid.

 

[Refueler]

I have a number of GPS units and if I have more than one agree to within 3ft / 1m .... then I'm happy ...

GPS is not the supreme cm accuracy some claim ....

 

[Buck Turgidson]

For real time accuracy of GPS and GPS with EGNOS look here: OPEN SERVICE REALTIME PERFORMANCE | EGNOS User Support