Which is the best chipset that provides the best accuracy. Which product provides the best accuracy on the market? Is there any product that be able to tell which lane a vehicle is driving in?


Thanks.

Most consumer-quality laptop GPS receivers cost around $40, $50, $60 USD. They work very well for the purpose they were designed for. They are rated, if my memory serves me, for accuracy of around 10 meters, or 30 feet. That is enough to tell you which street you are on, but not enough to reliably tell you which lane you are driving in.

However, even if you spend several thousands of dollars on a professional-quality GPS receiver that gives you sub-meter (or better) accuracy, you will not be able to tell which lane you are in, if you use consumer mapping products, which I'm afraid don't offer such accuracy.

Good point! I have been reading articles about accuracy, just as what you said, It is impossible to get the accuracy at that level.

Any recommendations in terms of quality, service. Price doesn't matter, as long as it not thousands of dollars.

Thanks Marvin!

Thanks for the clarity, I don't think accuracy within 30 feet should be a problem. Thanks again.

The over-the-counter programs are pretty much the same in terms of technology, accuracy, etc. The differences come in the interface, features, etc. For some, the DeLorme operation is tough. Actually, it's not tough, just different. S&T has a "Windows-style" interface and many people are familiar with that. Other features like construction updates, POIs, fuel consumption and cost, height restrictions, etc., are great selling points.

Regarding accuracy, there are variables, mostly dealing with reception. Tall buildings, cloud cover and antenna placement can affect the amount of satellite information being processed. If you're traveling I-40 in New Mexico with your antenna on the roof of the car, there's as much satellite information available as your computer can handle. If you're on Fifth Avenue in New York City in a rainstorm with the antenna on the dash, all bets are off.

If you need near-pinpoint accuracy.... well, it's high-dollar stuff and probably more than you'll ever need or would be willing to pay for.

I've been playing with consumer GPS for many years. Whenever anyone talks about the accuracy of consumer-grade GPS, the answer is generally quoted as X meters. The issue I've always run into is the fact that the GPS fix will never be consistent or repeatable. One minute, the fix will be 1/2 X meters south of the actual point. 30 seconds later, your fix will be 1/2 X meters north of the actual point. I've seen my house wander around the neighborhood at 2 MPH!

I have a USGS benchmark in my back yard. My handheld Magellan GPS can average your position over time. I've left it sitting on the benchmark for hours at a time, and the average usually works out to within a couple of feet of the actual location. Any single fix could be anywhere within a fairly large circle.

There is a PC application that will graph the GPS fix over a period of time (sorry, I don't recall the name right now) and display the track. You can watch the fix wander around in real time.

Rick

kc, interesting. At a stop in our rv (MR350, Co Pilot and Delorme SA) and on the bike ( Lowrance marine chartplotter with a 2 gig east coast inland map on a mini stick) when stopped the only value which dances around is the elevation everything else is, well, static-

Both installs have an external receiver/antenna

I'm betting that the software is filtering out the small movements in your position, at least horizontally. Now that I think about it, Streets & Trips used to show you moving around while stopped, but I don't believe S&T 2009 does.

You'd need to find one of the low-level GPS utilities that can display the raw fixes. The one I'm thinking of had a radar-scope display that showed the variation of the current fix.

When you hear of surveyors talking about 'differential GPS' they are measuring this inaccuracy in real time, and correcting for it. They set up a fixed GPS receiver right on top of a USGS benchmark, so they know EXACTLY where it is. The fixed receiver then compares the current GPS fix with the exact coordinates where the fixed receiver is located. It calculates the difference, and transmits that difference over a VHF radio link multiple times a second. The surveyor out in the field has his mobile GPS stick and a VHF receiver. When he takes a fix, his GPS fix is adjusted by the amount the fixed station is off. That's part of how they get centimeter accuracy.

Remember, the more birds you're picking up, the better your accuracy. If you're sitting at a light and the indicator is "bouncing" around, you may be picking up data from only 4 or 5 four satellites. If the indicator is steady, you're getting more data from more satellites and probably more accuracy.

I know this is an old thread, but I'm a new member browsing what's been talked about on this forum and when I read the quoted post I thought I'd chime in.

It's not necessarily true that more SVs = more accuracy. The geometry of the SVs and the receiver (which is constantly changing, even for a stationary receiver) is more important than the number of SVs the receiver is tracking. Ideal geometry is one SV directly over the receiver, and three more SVs just above the horizon at 120 degree intervals around the receiver (e.g., at bearings of 0+c, 120+c, and 240+c degrees from the receiver, where c is any constant). You could have 7 or 8 or 9 SVs in view and still have what I'd call crappy geometry if all of them are in the same part of the sky--much like when I sit on my patio and my receiver can only see the northern sky as the south is completely blocked by my house.

The goodness of SV-receiver geometry actually has a measure, and your receiver reports that measure--you just need the right software to see it. It's called "dilution of precision", or DOP, of which there are 5 flavors (Horizontal DOP, Positional DOP, Vertical DOP, Time DOP, and Geometric DOP). Whatever the flavor, smaller DOP numbers are better. If you have software that lets you see the raw receiver data in real time (Turbo GPS, Visual GPS, etc.) you can monitor all the different DOP numbers. You want HDOP numbers less than 1, though numbers between 1 and 2 are OK. With HDOP numbers above 3, I wouldn't consider my receiver's horizontal position fix to be very accurate.

I understand what you're saying and you're right, but generally, the more the better.

Of course, there is another variable: what is between the satellites and the receiver?

In urban areas (such as where I live) buildings near the receiver can alter the data. If a building interferes with the signal of just one satellite, you can see false movement of the indicated position.

In rural areas, heavy foliage overhead can interfere, too.

I suppose the cheaper the GPS receiver, the less accurate, but that's another thread.

Discussion about accuracy is right on. The geometry of where the satellites are, as well as the number of satellites, and the encoding used helps determine accuracy.

Some systems use both US and other countries' satellites for more accuracy. Plus differential GPS as mentioned. Accuracy can be down to inches or less.

As a side-note, the original consumer version of GPS had an accuracy of greater than 100 meters. The military version was much better. I'll let you speculate as to why that particular value.

Sorry, no consumer GPS is accurate down to anything like inches...metres maybe. The armed forces have access to an extra frequency to obtain higher accuracy but what you are talking about needs a fixed reference transmitter.

Terry

72 hours of fixes from a Garmin GPS 16x with WAAS turned off; GPS Standard Positioning Service. It's typical of what you can expect from a non-precision receiver. It's interesting how the fixes 'walk' .. they don't randomly sprinkle the map.

With WAAS (Differential GPS) the performance is much better.

--- CHAS

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There are non-military systems that have accuracies on the order of inches. They use carrier phase, as well as differential GPS to achieve this accuracy.

Reference: StarFire (navigation system) - Wikipedia, the free encyclopedia

Granted this is a 10K+ system, but it is available to consumers (in this case farmers).

Base stations for differential GPS are not designed to take into account movement of the station. There are stories about situations where the base stations moved due to external forces, thus invalidating the positioning data.

It seems to me that there is a lot of high quality GPS hardware available for very little now. On the other hand, the placement of the antenna with respect to its view of the sky seems to me to make a world of difference on the ability of a GPS to get a good fix quickly. If a laptop is expected to sit on the seat of a car with a USB dongle plugged into its side, that's a fairly difficult placement compared to the windshield mounts of many automotive GPS's. If you buy an active USB extension cable there is a 15 foot or so cable that lets you place the actual GPS in a window..that would help a great deal.

If you could access the crypto key, the Defense Advanced GPS Receiver (DAGAR) would be the most accurate laptop GPS.



The GPS Precise Positioning Service (PPS) provides real time accuracy in the order of two meters. DAGAR utilizes L1 and L2 (encrypted) band signals to remove timing errors introduced when signals transit the ionosphere. That's good enough for targeting GPS directed ordnance.

Prior to setting Selective Availability to zero, GPS was helpful for preventing you getting lost. Then everything changed when the Civil users found innovative applications for the full accuracy civil signal. Now the civil sector is driving the demands for accuracy and precision while the military is increasingly concerned about signal resilience during tactical jamming.

NASA is asking the Air Force to include laser reflectors on new GPS III satellites. That would allow laser ranging and characterization of orbits at centimeter levels reducing ephemeris errors to near zero. Evidently, the Air Force didn't require reflectors in its design requirements .. unnecessary for its military mission.

--- CHAS

You can get sub-meter accuracy with Trimble handhelds, but it's gonna cost you around $5,000.

Trimble - GeoExplorer 3000 Series GeoXT Handheld
Trimble - Mapping & GIS - GeoExplorer 6000 Series GeoXT Handheld