Bruce In Philly

Minutia alert! Warning: Nothing important here!

2009 C2S 93K miles

I noticed when I was on the highest point on I80 east of the Mississippi, my GPS was just plain wrong.

Actual: 2,250 ft
Porsche GPS: 2,190 ft

Folks, that is a whopping 60 feet error! How are we to survive?

We got issues.

Peace
Bruce in Philly

jhbrennan

Just be glad it's not being used for a precision aircraft landing.

LexVan

What's giving you the "actual" reading?

WV997S

I ride Road Bicycles with a Garmin 810 and they can vary based on the weather. When in Florida last week I noted as much as 20 ft difference in the same spot on different days.

Bruce In Philly

You can configure the PCM screen to show some data points such as altitude, number of satellites.... other stuff. Easy to do.... I don't remember which screen but it is one of the Trip then Option screens..... don't remember off hand. I think it is called "Personal Trip Data" or something like that.

Ooops: EDIT: Actual...... a big sign on the highway that said something like "highest point on I80 East of Mississippi"... I've passed that sign many times in 20 some years.
https://en.wikipedia.org/wiki/Inters...n_Pennsylvania
https://en.wikipedia.org/wiki/Inters...hest_Point.jpg

Peace
Bruce in Philly

Lahainabry

I notice mine is off at times. I drive PCH, it shows me in the ocean.
Couple days later, it is fine.

nwGTS

Sea level has risen 60 ft since that sign was put up. /s

BoomC2S

Did you take into account that 60 FT rise to the right of the sign on the highway?

DC911S

GPS receivers have known errors in its calculations for altitude, its well known and thats what its augmented for any kind of usage for aircraft approaches or landings. The geometry of the constellation has quite a lot to do with it, as the receiver does the calculations. The satellites just send timing signals and ionospheric correction via the WAAS, the GPS receiver in the car does the processing and figures out where its located and then uses the CD-rom road map to place the little icon. Plus not all the maps you see use the same datum as GPS, which is WGS-84. There can be quite a difference between positions and altitude calculations when different datums are used. Most older maps and road signs are not based on WGS-84. So there you go.

yvesvidal

How did we make it when there was no GPS?

We had maps, celestial navigation, good sense and orientation. Plus we knew how to find the North by looking at the sun and the moss on the trees. And I still use my ears to feel the elevations and the pressure differences.

Yves

nwGTS

WRONG

gota911

Bruce,



It's a good thing you weren't flying a plane and attempting to land it in foggy weather. You would have overshot the runway and crashed, thinking you were 60 feet lower than you actually were at the time.

Relatively speaking... the 997.1 IMS issue doesn't sound so bad now!

Carmichael

The only reason I'm miffed that my car doesn't have GPS is because I have a big honkin' LCD screen in the dash.

Damn thing weighs close to 10 lbs ...

I love driving through that stretch of I-80, through western Pennsylvania. I make the journey maybe once a year or so to visit my fiancee's parents in Baltimore. We normally make the trip in our E300 Diesel, but we've done it before in my old Cooper S.

The fast, sweeping corners are fun late at night, but you've got to watch out for wildlife crossing. I've come close to making Bambi Burgers many a time. In the Mercedes, we usually make it from Chicago to about 100 miles out of Hagerstown, MD.

My only requirements for that drive are a 4 pack of RedBull, a good Vocal Trance playlist, and fuel.

Edgy01

Did you remember to set the local altimeter setting before you looked at the elevation reading?

Dennis C

If you have a 997.1 with PCM 2.1, this is NEVER an issue! The rock solid PCM 2.1 system never provides you with an incorrect altitude reading.