I Google earthed my Prius GPS - waay off

Hmmm. When my wife gets home I'll compare the nav system coordinates on the Prius and out Volvo XC90, and then cross reference it with Google Earth. I'll let you know.

 

Humm, my first thought is that they may be using different GPS coordinate systems, but my second thought was that probably isn't it.

I am under the impression that the Russian GPS system and satellites are totally different than the system we use in the US.

As a matter of interest, here is a url which describes three of the different systems.
http://www.paddles.com/users/wildcamp/coordexp.html

Even so, I think you are going to find another explanation.

How's the weather up there in Hudson's Bay? :lol:

 

Well, I checked the nav systems in both cars, and they were virtually identical. The Longitude was the same for both systems, and the Latitude was off by only one second. Does anyone know how much distance is represented by one second?

Now, I compared it to Google Earth, and the values were identical. All three sources gave identical values.

I'm not sure if the problem is with your nav system or with your plot of Google Earth.

 

About 100 feet (30m). I thought I read somewhere that the absolute accuracy of GPS was better than that, these days. So, it could be a zero-point offset. On the other hand, it could be siginficantly less than 1 arcsecond, and the rounding is handled differently in the different systems?

 

As I suspected, the GPS accuracy should be much better than 30m. . . in fact, it should be more like 3m.

Check out this guy's page (and his main page) for more information than you could ever desire about GPS error.

 

Check to see if it get better when you pull it out of the garage.

 

Standard GPS is about 30 meters WAAS (Wide Area Augmentation System) enabled GPS is supposed to be generally accurate to apx 3 meters... since even my $150 elcheepo Garmin and Magellan units have WAAS as does my PDA it should stand to reason the Prius system should be WAAS enabled, can anyone confirm that?

The WAAS i am familiar with is 25 stations or so in the US if you are not in the US this feature may or may not be available <shrugs> just a thought. Even if it isnt I should think the accuracy should not be off by hundreds of miles... I have seen heavy cloud cover prevent me from getting a signal on my GPS units.

 

Yes, it could be either of those. My guess is that one system round up and one rounds down.

 

Russian GPS? AFAIK, the US is the only country with 24 satellites positioned around the earth which provide triangulation signals to GPS devices.

The USAF has built-in an error factor to all GPS signals to prevent our enemies from using our GPS signals against us. In order to access the actual accurate GPS signal (called the Y-code), you must have a special crypto code and the equipment to use it.

So expect some errors.

 

Think this is what I was referring to .....

There are currently two "public" GPS systems. The NAVSTAR system is owned by the United States ... The GLONASS system is owned by the Russian Federation.

http://www.redsword.com/GPS/apps/general/how.htm

 

apparently europe is sending up some competitors for the GPS system called galileo satellites. should be interesting to see how well they work and how long it takes to get the system up and running.

http://www.nature.com/news/2005/051219/full/051219-16.html


glad to hear you figured the issue out, imntacrook. the first rule of science is 'never get excited over anything until you can repeat it'

 

Finally!! Somebody's got teleportation technology worked out....

 

Because of the nature of GPS, latitude and longitude are fairly accurate, within 3 to 10 meters. Elevation has a variance of plus or minus 100 meters. A GPS receiver needs to "see" at least four satellites to find a position. The US military has been known to "tweak" the system from time to time. Your unit may need to be re-set up or calibrated for North America.

 

I think some may have missed this when you said it...

 

Glad he's not a gunner in the military!

 

glad you turned out not to be in hudson bay. i hear it's cold.

couple of things about GPS... first of all, a GPS needs to "see" only three satellites to get a fix for latitude and longitude... seeing a fourth satellite gives you altitude. but for a car, altitude is slightly less important than for a plane.

also, the WAAS system is nice, but chances are your receiver isn't picking up a WAAS signal much of the time, since WAAS transmitters are terrestrial (on the earth) and easily obscured by buildings, mountains, etc.

according to (the sometimes dubious) wikipedia, GPS accuracy can be as good as one centimeter.

 

Posting this will just confuse people -- The 1 cm quote was using differential GPS, which neither the Prius, nor any other car, has. Differential GPS is when you have a local fixed ground station in a known position receiving the GPS signal, determining the error by subtracting out its known position, then transmitting this error to specially-equipped mobile units so they can subtract it from their readings. To get down to 1 CM, the mobile unit would still need to average several readings in a fixed position. None of this applies to a Prius.

Personally, I'd like to see this thread die, as its posting was a mistake from the get go. Maybe a new thread on GPS theory?

 

well if latitude is the measure of distance going north/south from the equator and if the distance between the poles is half the circumference of the Earth at the poles (24,860 miles)

AND

if 60 seconds =minute
and 60 minutes = degree
and 360 degrees makes the distance to measure then

a second would be 101.2 feet