GPS accuracy limitation

[cprince]

I have a nuvi 885t, and it seems that the accuracy is fixed at 10 feet(~3 meters). I've never seen the accuracy below 10ft, even in clear sky and fixed on 12 satellites. According to the user manual, this GPS is WAAS-enabled. Also according to Garmin, the typical WAAS position accuracy is less than 3 meters:

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

There's no way to change WAAS status in the settings. Does anybody know of any law/regulation that limits the accuracy of civilian GPS to 10ft? Thanks.

 

[CycloWizard]

IIRC, civilian units are limited to 10 ft resolution by statute, while some military units have 1 ft resolution. I'm not sure why any civilians would ever need higher resolution, and only a couple reasons why the military would want such high resolution. The military developed it and civilians can use it free of charge subject to the resolution limitations. I might be remembering incorrectly, but I'm pretty sure that's the case anyway.

 

[cprince]

I think you're correct. I looked at some high end hand held units from garmin, and they all have 10-15 feet accuracy with WAAS enabled and <33ft with WAAS off. I don't mind having a maximum of 10ft accuracy, but sometimes when I'm driving in next to a parallel road, the GPS thinks that I'm on the other road.

 

[BeerdedOne]

There is no such limitation for civilian GPS resolution. At one time, real time signal resolution was limited by the US gov, but that limitation was turned off during the Clinton administration. Current professional GIS survey instrumentation can produce sub-centimeter accuracy reliably (these units are stationary).

There are many different sources of error in GPS which contribute to less than optimal accuracy. The WAAS feature addresses only one aspect of GPS signal accuracy by relying on positional data from nearby GPS base stations encoded in the satellite signal. A whole host of other factors can prevent consumer grade devices from achieving anything close to their potential accuracy. Have a read of this text, by the end of the chapter you'll have a good idea of the basic considerations in GPS accuracy:

https://www.e-education.psu.ed...eofgeoinfo/c5_p19.html

 

[jagec]

There is no such limitation for civilian GPS resolution. At one time, real time signal resolution was limited by the US gov, but that limitation was turned off during the Clinton administration. Current professional GIS survey instrumentation can produce sub-centimeter accuracy reliably (these units are stationary).

To be fair, though, the sub-centimeter accuracy is not real-time, but is calculated later based on published satellite data (after it's been corrected for gravitational anomalies).

GPS is truly an awesome technology. That kind of accuracy over that dynamic range is rarely seen.

 

[0roo0roo]

also, map inaccuracy. world is not a perfect sphere, its a bit wonky. simplified models are used to get things to run on simple devices.

 

[Lemon law]

Just a random thought, but a highly accurate GPS system could be a basis for a robotic
car navigation system. But in any such system 3 meters would not come in close to fitting
any existing road systems, but plus minus one foot could be a basis for such a technology.

 

[l0cke]

Has anyone seen this?

http://blog.makezine.com/archive/2009/11/diy_real_time_kinematic_gps.html

They claim centimeter accuracy, which would be usable to have a car drive itself.

 

[MStele]

I'm a geologist that does survey work, and I can say that there are no built-in limits on gps accuracy, however gps by itself isn't accurate enough for many applications. We use multiple gps units to get an average, then use land based positioning systems to increase the accuracy down to a few centimeters.

No GPS device alone can achieve 1 cm accuracy. There are atmospheric conditions to consider as well as other limiting factors.