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Do all newer Garmin's GPS use WAAS?

Garmin's web site and the salesmen talked about how WAAS improve the accuracy of GPS.

Do all newer Garmin's GPS use WAAS like the Nuvi 255W?

Comments

  • Tim 1271 Points
    No, and it is a good thing most of them don't. WAAS will increase the accuracy of your calculated position by a couple of meters. But in an auto GPS... that won't make any difference. The underlying maps are not close to being that accurate, so it won't make any difference to you as a user. WAAS also draws down the battery faster. So for cars there is no real positive (and a few negatives) for using WAAS. That is why it is turned off on many auto GPS devices that would otherwise had the hardware to support it.
  • Could you explain this why it is not as good.

    According to http://www8.garmin.com/aboutGPS/waas.html

    With WAAS, the typical accuracy with WAAS is within 3 meters, without WAAW the typical accuracy is within 15 meters. So are you saying the additional 12 meters (about 39 feet) does not mean that much?
  • Tim 1271 Points
    So are you saying the additional 12 meters (about 39 feet) does not mean that much?
    Correct, that is almost exactly what I'm saying. But I wouldn't use the word "typical". Without WAAS your calculated position will be accurate to within 15 meters 95% of the time. With WAAS your calculated position will be accurate to within 5 meters (I think 3 is a stretch) 95% of the time.

    So without WAAS that doesn't mean you are only getting 15 meter accuracy. 95% of the time it will be better than that. So the difference between them can't be calculated as 12 meters (15-3).

    The road network isn't mapped with that degree of accuracy, so thinking back to high school math class regarding precision, the accuracy of the GPS/map combo is only as strong as the weakest link... in this case the underlying map.

    You will never notice the difference driving down the road if WAAS is available and turned on, versus it being turned off-- with the exception that your battery will drain faster with WAAS on.

    Even at a slow speed of 25mph the difference (12 meters) goes by in about one second. The refresh rate of the map screen is typically about one second.

    So the difference between WAAS and no WAAS in a car is irrelevant.
  • gatorguy 191 Points
    One of the better explanations :D
  • Thanks, I have read a lot of your posts.

    Some additional questions on accuracy:

    I've been thinking of getting a 255W for the second car. I have a build-in one on my Honda. I have notice that sometime the car position is incorrect and off the road. In about a second or two, the position jumps back onto the road.

    I am assuming this is because the GPS knows that I'm not driving on my neighbors' lawns and must be on the street, so it puts me on the street. Do all auto GPS systems like the Garmin do this?

    What happens when you go into a long tunnel? My Honda uses the speed input from the car and has it own inertial compass. Boston, where I live, has the Big Dig. So my display shows no GPS signal but still is very accurate when I come out of the tunnel, no matter if I'm speeding along or stuck in traffic while in the tunnel. What will the Garmin 255W do in this case? Does it just say no GPS signal and stop working until I come out?
  • Tim 1271 Points
    I am assuming this is because the GPS knows that I'm not driving on my neighbors' lawns and must be on the street, so it puts me on the street. Do all auto GPS systems like the Garmin do this?
    Correct, once your calculated position is 'close enough' to a road for the GPS to assume you are on the road, it will "snap" your position to the road. This is how almost every auto GPS operates. It is actually quite interesting to turn that "snap" feature off on devices that will allow it. You get a false sense of accuracy when the GPS always draws you on a road and when the feature is off you will see yourself driving beside the road as often as you drive on it. :)

    With regard to tunnels, I'm not sure if your car tries to "keep up" while you are under a tunnel, but the Nuvi 200 series won't do that. It will simply say 'lost satellite signal' and then constantly keep trying to lock on. Within a few seconds of being back above ground it will regain the signal and keep going.

    Many factory-installed GPS systems will have a speed sensor cable... Basically the GPS becomes aware of what the speedometer says. It will then guestimate your position based on the speed and assuming you are not missing any turns while underground.

    Some PND devices like the TomTom 900 series use accelerometers to help judge your position while in tunnels-- it doesn't perform as good as GPS, but it is nice to have if you are driving in unfamiliar underground locations. That is why I always take a TomTom 900 series with me into Boston... I still get lost in those tunnels.
  • TT 900s have a gyroscope too, to estimate direction of travel.
  • gatorguy 191 Points
    I'll see if I can find the info, but I recently read that one of the chip makers is adding accelerometers to their integrated design.
  • Sirf/Centrality?

    More on EPT:

    Yournav.com

    EPT is TomTom newest positioning technology which should enable the device to calculate its position, and continue navigating, even if the GPS signal is lost. Think navigating in urban areas, with high buildings, or through tunnels and beneath bridges here.

    In the very first GO, which is now commonly named the ‘GO Classic’, TomTom also tried to do the same with their Automated Satellite Navigation (ASN). This solution was largely in software though, and turned out to perform below standard. In the 920, hardware solutions like an accelerometer and a gyroscope were built in, and TomTom firmly believes this option is a much better solution.

    During our tests, we’ve tried EPT under different circumstances, and even though the SiRF Star III chipset does not easily loose its satellite fix, we found it’s handy to still have EPT around as a backup.

    At the start of every route, the system needs some time to calibrate itself, but in practice the user doesn’t even notice this. Then, when entering a tunnel for example, the system will flash the ‘EPT’ icon in the status bar of the unit (see photo to the side). Despite the colour of the route data and distance to next turn changing from white to light grey, the cursor continues to keep up with the movement of the car. The voice commands also remain unchanged.

    During our tests EPT proved to be reliable. When the speed changed inside a tunnel, the cursor on the screen adapted nicely to the new speed, and in the case of trickier situations like exits from a tunnel, EPT proved to be a handy new feature. We also found that EPT still works when no route is planned. The question remains of course whether this new feature justifies the expense of buying a GO 920.

    -----------------

    Tomtom:
    Enhanced Positioning Technology
    For a more continuous navigation experience
    Enhanced Positioning Technology (EPT) is used to estimate your current position when GPS reception
    is unreliable or unavailable. When satellite signal reception is compromised, for example when driving
    between tall buildings in metropolitan areas, EPT offers a more continuous navigation experience.
    At the beginning of a journey it takes about one minute for EPT to fully calibrate. Once the device is
    docked in the car, with good GPS reception and at a standstill, it calibrates for five seconds. Then, for
    one minute after setting off, the calibration engine collects data from the sensors.
    EPT features an accelerometer and a gyro. Data from the sensors is matched against the map data
    to estimate your position. And it works whether you have a route planned or not. This means that you
    can continue to navigate along your planned route when GPS reception is temporarily unavailable.
  • gatorguy 191 Points
    No, I thought it was Blox but I haven't had a chance to check yet
  • Tim 1271 Points
    Something else about WAAS that is worth mentioning... The GPS satellites are supposed to travel in their designated orbits. Sometimes they can be a little "off" from where they are supposed to be. The WAAS system calculates how much they are off, and provides correction information to your GPS.

    So if all of the satellites were exactly where they are supposed to be, no correction information would need to be applied. Therefore your position wouldn't be any different, WAAS or no WAAS. Of course that doesn't happen and correction information does help, but depending on how far "out" things are, the satellites you are connected to, etc the benefit won't always be significant.
  • One more bit of WAAS trivia: The technology was developed for the aviation GPS user segment. The real benefit of WAAS in air navigation is that the GPS-derived altitude is considerably more accurate than both non-WAAS GPS altitude, and barometric altitude. This lets you fly a GPS instrument approach in lower cloud ceilings, and lower visibility, than a non-WAAS approach. Prior to WAAS, GPS approaches were flown with altitude information from a barometric altimeter.

    Of course, altitude accuracy doesn't matter much to car navigation, unless you plan to become airborne now and then. :lol:
  • In addition to the ephemeral corrections that Tim mentions, the WAAS also provides correction data for ionospheric errors which can be as high as 10 meters. The WAAS satellites collect iono error data from a network of thirty seven WAAS reference stations (WRS's) located in conus. A list of WRS coordinates can be found here:

    http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System.

    The iono correction data is then retransmitted to end user receivers. The iono correction grid offered by WAAS is then interpolated and applied by the receiver. For these corrections to be effective, the end user must be within 500 nm of a WRS otherwise the corrections will degrade with distance from the WRS. Prior to WAAS, the reciever utilized an ionosperic model programmed into its memory.

    I tend to agree that, it is doubtful that WAAS enhances the use of GPS for automotive purposes but it does not degrade it either.
  • Tim 1271 Points
    I tend to agree that, it is doubtful that WAAS enhances the use of GPS for automotive purposes but it does not degrade it either.
    Agreed, except for battery life. But even then most people are powering their GPS in the car.
  • i still like waas if its there.
  • SergZak 217 Points
    I seem to recall that there is some processor overhead involved with WAAS (thus the greater battery drain), especially if it is enabled and the unit continues to search for the WAAS birds if it can't find them. If the processor is already maxed out, and if WAAS is available and enabled on the unit, I bet you'd see some performance degradation in one way or another.

    Having WAAS disabled by design may just be a good thing, especially with the already taxed nuvi 7x0 processor.
  • Tabs 0 Points
    Something else about WAAS that is worth mentioning... The GPS satellites are supposed to travel in their designated orbits. Sometimes they can be a little "off" from where they are supposed to be. The WAAS system calculates how much they are off, and provides correction information to your GPS.

    So if all of the satellites were exactly where they are supposed to be, no correction information would need to be applied. Therefore your position wouldn't be any different, WAAS or no WAAS. Of course that doesn't happen and correction information does help, but depending on how far "out" things are, the satellites you are connected to, etc the benefit won't always be significant.
    Yeah I was gonna post exactly this - I had the chance to fly an aircraft equipped with a WASS Garmin G1000 system last month with a friend and it's really amazing - we were doing fully coupled VNAV approaches right down to minimums just like you can in an airliner.
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