GPS or WAAS?

 

I know my StreetPilot c330 has the option for Normal (GPS), GPS off or WAAS/EGNOS.

I have played with both and found that the WAAS setting keeps up with my location much better at higher speeds (over 45mph), but worse at slower speeds, and the GPS setting is the opposite. So when I am around town I keep it set to GPS, and outside of town, I switch it to WAAS/EGNOS. I wonder if the expansive presence of military here lets one work better than the other?

From the information I have read about it, the WAAS is supposed to be much more accurate, within 3-7m (9-21 feet) when compared to direct GPS which is 21m (63 feet).

There is actually lots of info here:

http://users.erols.com/dlwilson/gpswaas.htm

Any other viewpoints on this?

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Garmin c330 w/ 2011 maps

Street Maps vs Open Field

For a street map, the critical factor is not the GPS but the map itself. Most maps do not have a specific lat/long for each address. Rather, they plot the lowest and highest numbers on a given street and divide the distance for the numbers in between. In some places NavTeq guesses better and in others Tele Atlas does. Neither is perfect 100% of the time.

If you are looking for a specific lat/long in the open, then WAAS will make a difference.

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Shooter N32 39 W97 25 VIA 1535TM, Lexus built-in, TomTom Go

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You'll notice in the link you provided, the word 'speed' isn't used when discussing accuracy. They only talk of horizontal and vertical position.

WAAS only deals with positional accuracy.

Speed is calculated simply by measuring the doppler shift of the satellite signals. WAAS should have no effect on speed. As a matter of fact, if you look at the specs for the C330 you'll see that the positional accuracy is much better using WAAS, but the velocity accuracy remains the same for WAAS or regular operation (.05 meters per second or 1/10 of a MPH)

http://www8.garmin.com/products/sp330/spec.html

Quote:

GPS accuracy:

Position: < 15 meters (49 feet), 95% typical
Velocity: 0.05 meter/sec steady state

GPS (WAAS) accuracy:

Position: < 3 meters, 95% typical
Velocity: 0.05 meter/sec steady state

Note that I'm not saying you aren't experiencing this.. smile I'm just pointing out that theoretically WAAS should have no effect on the speed reading..

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Right I understand that my speed or the speed of any receiver has nothing to do with the accuracy or how it relates to the maps themselves. I noticed that the WAAS setting tends to either lag behind or skip forward my location as show on the unit at slower speeds, versus the GPS setting does this at higher speed.
I was pretty much asking if anyone else had noticed similar findings... or does everyone have newer units that do not have the WAAS option? or do the newer Garmin Nuvi units automatically use WAAS, and not just GPS?

As a side note, I do understand that WAAS is just an expanded implementation of GPS but uses a bit different "correction" factor.

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Garmin c330 w/ 2011 maps

You may want to look at this

You may want to look at this post http://www.poi-factory.com/node/10647 and the other posts listed with it.

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Charlie. Nuvi 265 WT and Nuvi 2597 LMT. Android Here WeGo - Offline Maps & GPS.

WAAS was intended for air

WAAS was intended for air navigation. The increased accuracy helps aircarft throughout flight, but is most important for precision approaches.

I noticed that the display mode of the screen has a lot of effec

talikarni wrote:

Right I understand that my speed or the speed of any receiver has nothing to do with the accuracy or how it relates to the maps themselves. I noticed that the WAAS setting tends to either lag behind or skip forward my location as show on the unit at slower speeds, versus the GPS setting does this at higher speed.
I was pretty much asking if anyone else had noticed similar findings... or does everyone have newer units that do not have the WAAS option? or do the newer Garmin Nuvi units automatically use WAAS, and not just GPS?

As a side note, I do understand that WAAS is just an expanded implementation of GPS but uses a bit different "correction" factor.

In playing with my unit (a plain 3.5 inch Nuvi 200) the display mode on the screen has a lot to do with how "accurate" the display is as to position. When in North Up or 3-D, the screen update was jerky and slow often showing my vehicle still approaching an intersection I had passed. The screen would then "jump" and update showing me past the intersection. This was not the behavior I noted while in 2-D mode. This scrolling is very smooth and the map keeps pace with my vehicle.

As to the correction factor - WAAS uses an in-band signal to apply correction data to the signal received allowing position accuracy to a few meters. Differential GPS or DGPS uses an external ground-based transmitter site to broadcast a correction signal and the accuracy is down to about a centimeter. Surveyors use DGPS which needs two receivers - one for the satellite, one for the differential signal

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ɐ‾nsǝɹ Just one click away from the end of the Internet

aircraft

based on the mention of aircraft, I am thinking that was I was saying may actually make sense since most aircraft even when taking off or landing are still going well over 50mph.
Sounds like I will pretty much keep it as is, use WAAS for highway travel and GPS for around town.

As for the lag of 2D versus 3D, I have tried them both and I got the same results. It must be how the StreetPilot is designed to render your location compared to the Nuvis.

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Garmin c330 w/ 2011 maps

WAAS

jwt873 wrote:

Speed is calculated simply by measuring the doppler shift of the satellite signals.

I would think that speed is determined by taking change in distance / change in time. That would be more accurate and easier to calculate than to adjust for cosine errors for up to 12 different signals.

WAAS is used to help accuracy due to errors by atmospheric conditions. My Nuvi 750 does not receive any of the WAAS birds so no WAAS information is used.

http://gpsinformation.net/exe/waas.html

WAAS

I have mine set on WAAS all the time. The only disadvantage is that it uses more power according to the documentation.

Not exactly

talikarni wrote:

I know my StreetPilot c330 has the option for Normal (GPS), GPS off or WAAS/EGNOS.

WAAS is a correction signal for GPS operation. It cannot be used with GPS turned off, IMHO. Not really sure if you meant it that way or not.

GPS Off is for simulation.

GPS Off is for simulation.

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Frank Nuvi 3597LMT 37.322760, -79.511267

off

phranc wrote:

GPS Off is for simulation.

right sometimes I will be playing with it indoors, loading custom POIs, or updating maps and rather than wait for it to say "poor/no satellite reception", usually I just go in and turn it off.

I just stated the choices in the order they are listed in my unit:
GPS (on), GPS off, WAAS

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Garmin c330 w/ 2011 maps