WAAS vrs CIRF III

I don't know the answer to your question, however, I do know that enabling the WAAS on my Garmin 660 made no difference in it's accuracy.

Haven't noticed a difference in my unit either, although default (from Garmin) is off. I have read elsewhere that it slows down displays, decreases battery life, and is included on nuvi 660 only to be backward compatable to units w/o CIRF III.
When checking SAT strength, my unit only gets to 27' accuracy, either with or without WAAS.

Here is a write up on Wikipedia on the SiRF Star III.

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

I personally think it is faster and more accurate vs. standard Garmin WAAS, but there are some generic chip sets that are as quick (MTK chipset found on some bluetooth GPS units from Taiwan).

Sanger

Assuming you mean SiRF III, they two things represent two different things.

The SiRF III is a GPS chip controller contained in many newer GPSr. The SiRF III can acquire the GPS signal faster and under dense coverage such as trees. It also can listen for signals from 20 different GPS satellites at the same time. It is an improvement over previous chip technologies.

WAAS is a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message.
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According to manual from Garmin c530, accuracy if set for normal is less than 10 meters and if set for WAAS, less than 5 meters. Setting to WAAS will lower the battery time as it uses more power.

Actually depending upon where you geocache, the SiRF III can be very helpful if you are under dense tree cover or urban situations. The chipset will be able to lock the signal in better than other chipsets.
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Very well said MM are you in the communication industry or just knowledgable in these matters?

Ray

Actually it is excellent under those conditions and also in valleys and urban canyons as well. I use a Magellan eXplorist 200 for geocaching and find it does a decent job for a simple patch antenna unit.

Ray

The SIRF-equipped StreetPilot c530 can get a fix inside my house; the non-SIRF StreetPilot i5 could not.

SiRFstar III does give enhanced reception and some in-building penetration, but I found that accuracy is better too. I took my boat out last Monday, set my old eTrex next to my Mio, eTrex with WAAS enabled, Mio on SiRFIII, and first it took the eTrex about twice as long to get satellite sync, then while transitioning the lake on known tracks the eTrex varied quite widely on current position versus the Mio.

The other thing I noticed is that I really had to move off the track quite a bit (several yards) before the eTrex registered the change, while all I had to do was very the steering just slightly and the Mio picked up the change.

Many people don't see any gain from WAAS, but without it my eTrex, at least on Lake Norman, was almost worthless.

I'm a little confused by the back and forth discussion on this thread. It was my understanding (as stated in other responses on this thread) that SiRFIII is the chip. It was also my understanding that WAAS uses additional satellites to provide potentially better accuracy. If my understanding is correct, then using a GPS that has a SiRFIII chip (such as my c530)will provide a certain degree of accuracy and turning on WAAS on my unit will potentially increase that accuracy. The advantages (accuracy, reception,etc.) for SiRFIII are obtained when through the GPS you decide to purchase. The usage of WAAS (if available on the unit) will increase accuracy with a slight hit on speed and a hit on the battery time.
I always leave WAAS on and usually run from a power source. When I use the unit out of the car, on battery, I make a determination on how long I will be using it and if it is greater than 4 hours, I switch WAAS off (normal) and expect about 7 hours.

You are entirely correct.

Thanks for the sanity check

What do you mean when you say that WAAS is slightly slower than SiRF? If you are refering to the position updates, I thought all GPS update times were once every second? Or are you talking about satellite aquistion time, route recalculation, map drawing, etc?

Ever since the first time I used my c550, I've had WAAS turned on. This thread is making me start to wonder if I should try turning it off for a while.

I was talking about satellite acquistion time. I don't think it is a big deal. As I said, I usually have WAAS engaged.

Thanks, Ray.

I'm not in the industry. Just knowledgable, I guess ... and geeky. Plus I've been GPS-ing for a long time.
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Actually, WAAS doesn't "use more satellites", it uses ground stations to assist in satellite triangulation. It was going to be a big deal and the military was pushing for it but it's never really gotten off the ground, commercially.

According to Garmin's WAAS site (http://www.garmin.com/aboutGPS/waas.html) they say that WAAS enabled receivers are up to 5 times more accurate, as the ground stations help provide GPS signal correction. I had to use my eTrex on WAAS enabled most of the time or my positioning on Lake Norman was way off. The downside of WAAS is that it's a battery eater. My battery time was cut by about 55% using WAAS.

Read Garmin's excellent description of the technology, it'll enlighten you if you haven't seen it before. I was involved in some military applications of this in it's infancy, but that was a lifetime ago.

Also, go look at the Wiki site referring to SiRFstar III chipset, it's one of the best descriptions I've read so far. http://en.wikipedia.org/wiki/SiRFstar_III

WAAS uses ground stations to send corrections to the satalites to "do away" with orbital and other type errors in the satalittes reporting and will improve accurcy about 4 or 5 times, depending on your area of the country. It was put in to improve the aviation accurcy, especially altitude, but it gives all of us users what is essiently differential corrections without having to use a differential transmitter.

SIRF III is a chip set to read the satalites and is much more sensitive than the older ones.

Something I just found out today from Mio-tech, that my Mio C310x uses the SiRFstar III chipset and is WAAS enabled. I didn't know that, but no wonder it's so much more accurate than both my Magellan and my Garmin. Guess I got the best of both worlds!?!

My experience with A Garmin C550 is it takes 1 minute longer to acquire satellites with WAAS selected. In the city the accuracy was the same.