Accurate Consumer Gps: 2.2m (waas) Is Best?

[jbeale]

The best accuracy spec I have seen published for a consumer GPS unit is for a GPS "mouse" type device. The Holux GM-210 using the SiRF Star II or SiRF Star IIe/LP chipset, claims 2.2 meter accuracy when receiving WAAS signals:

http://www.holux.com/product/gpsreceiver_m...vel=grandsonson

 

EGNOS/WAAS/Beacon Position

< 2.2m, horizontal 95% of time

< 5 m, vertical 95% of time

 

Advertised accuracy for the newer models, eg. SiRF Star III seems to be lower: 5 m or 10m horizontal position. Is there any consumer GPS unit that does any better than the old Holux GM-210 ? The older (pre-SS3) Garmins like the GPS 60 advertise 10 feet w/WAAS which is about 3 meters. The newer GPSMAP 60Cx advertises 3-5 meters w/WAAS.

 

For that matter, is this WAAS 2.2m / 95% spec. from Holux a reliable number? It agrees with the FAA page that claims WAAS can deliver 1-2 m accuracy for ground vehicle navigation, not just aircraft http://gps.faa.gov/FAQ/faq-waas.htm#34 but if that's real, why can't the other manufacturers do as well as Holux?

[+Timpat]

I can say from experience in the field that my Map 60CX w/SiRF Star III, w/WAAS enabled, regularly gets me +/- 2 meter accuracy, and virtually ALL the time is within +/-5 meters. I base this on comparisons with Trimble Pathfinder ProXR sub-meter units where I have been taking companion shots when out capturing GPS data. True, I don't see this advertised, or claimed, by Garmin, but this is my observation.

[+cron]

With my 76S, I was getting about 4-5 meters with WAAS and clear view of the sky, and mainly 6-8 meters all around.

 

With my 60CSx, I'm getting 2-3 meters with WAAS and clear view of the sky, but I never go higher than 5-6 meters in worse conditions. I would say it keeps 3-4 meters almost all times.

[jbeale]

I can say from experience in the field that my Map 60CX w/SiRF Star III, w/WAAS enabled, regularly gets me +/- 2 meter accuracy, and virtually ALL the time is within +/-5 meters. I base this on comparisons with Trimble Pathfinder ProXR sub-meter units where I have been taking companion shots when out capturing GPS data.

Thanks, that is very useful to know esp. since you have a high-quality receiver to compare it with. I'm also sure that any receiver will have poor performance in sites with significant multipath, though maybe the professional gear is less affected (choke-ring antennas etc).

 

I guess what I'm wondering is, does the difference in the accuracy specs mean one company is more conservative about what they claim, or that they tested in different environments, or is it really a difference in the device itself? I wonder, when I see a claim like accuracy = X m / 95% does that mean typical? Median expectation value? Best they ever saw? Theoretical but not measured? Perhaps the question should be directed at the manufacturer, rather than a discussion group but I'm just wondering.

[+cron]

Let's be honest... If they start advertising "real tested numbers", it will be something like:

 

- setting up a GPSr on top of a building on a wonderful summer day

- save data over a period of time

- advertise these numbers as "real-life"

 

For what it's worth...

[+Timpat]

I believe the makers of the SiRF III chipset (and thus Garmin) are keeping the accuracy claims on the conservative side. Maybe due to the fact the SiRF III can pull signal in poor conditions such as under foliage and indoors in some cases. In these instances for example they couldn't claim 2-5 meter accuracy due to multi-path signals, etc. So, they have to reach a balance in the stated claims of accuracy. The 95% statement is a statistical value but I can't personally expand on that.

 

To address your question, "I wonder, when I see a claim like accuracy = X m / 95% does that mean typical?", I found this from the National Standard for Spatial Data Accuracy (NSSDA) website: "The NSSDA is a 95th percentile standard, which means that when test points (at least 20) in the dataset are checked against an independent dataset of higher accuracy covering the same area, 95% of those test points must be within the reported accuracy value".

 

Hope this sheds some light on this subject.

[+dino_hunters]

with my explorist 500, I often get 6' (1.8 m) accuracy in an open area. thats with 2 waas sattelites locked on.