Issue with Altimeter showing too high?

[ljump12]

I have a '21 Taycan Cross Turismo, and the Altimeter seems to consistently show ~85ft too high. I live in a coastal town, and I've never seen it below 80ft (even when I'm parked next to the sea). When I asked the dealer about it, they told me the altitude comes from the gps/map data, and there's not an actual altimeter on board.

Has anyone else experienced this? Is there a way to calibrate it? It would bother me less if I didn't opt for the compass option where it's always shown in the middle of the car.

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[slothinker]

Yes, I also live in a coastal town and have noticed readings which seem about 100 feet higher than what I'd expect. Perhaps the +/- for the Porsche altimeter is about 100 feet? Wouldn't make much difference in New Mexico or Wyoming but quite noticeable adjacent when driving adjacent to a beach such as north of Santa Barbara.

 

[JimBob]

I think this is the first time anyone has brought this up. I just checked this on my car. You probably need to download Google Maps Pro to get an altimeter reading, but it gives you the height of the camera so not really useful. In my case the height of the camera is 682 meters and the altimeter reading from the car is 172 meters. The actual height for my area is about 170 meters above sea level, so it looks pretty accurate.

Interested in what other people say.


Edit
You should have a geodetic marker somewhere in your area which will give you the exact height above sea level. If you are in the US you can find the nearest marker at this link https://geodesy.noaa.gov/

 

[ljump12]

You should have a geodetic marker somewhere in your area which will give you the exact height above sea level. If you are in the US you can find the nearest marker at this link https://geodesy.noaa.gov/

Thanks for the link, I have an "Orthometric Height" of 2.6 (which I take to mean 2.6 meters) near my house. The Porsche shows 88ft.

 

[Pinballplanet]

I have a '21 Taycan Cross Turismo, and the Altimeter seems to consistently show ~85ft too high. I live in a coastal town, and I've never seen it below 80ft (even when I'm parked next to the sea). When I asked the dealer about it, they told me the altitude comes from the gps/map data, and there's not an actual altimeter on board.

Has anyone else experienced this? Is there a way to calibrate it? It would bother me less if I didn't opt for the compass option where it's always shown in the middle of the car.

I had the same thing with my 2020 panamera fwiw

 

[OTPSkipper]

The car gets its altitude from gps I think. GPS altitude is not that accurate. The angles between the car and the sat are not very big, and it makes it hard to be accurate on altitude. Mine is the same way.

 

[JimBob]

From Garmin

Understanding the Accuracy of the GPS Elevation Reading
GPS heights are based on an ellipsoid (a mathematical representation of the earth's shape), while USGS map elevations are based on a vertical datum tied to the geoid (or what is commonly called mean sea level). Basically, these are two different systems, although they have a relationship that has been modeled.
The main source of error has to do with the arrangement of the satellite configurations during fixed determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.

It is not clear how these elevations are actually measured though maybe not important with a Taycan which is generally stuck to the ground. Maybe best to test over a range of locations to see how it changes. Clearly the USGS are the more accurate measurements.

Edit
It appears that the higher the altitude at which you are measuring, the more accurate the measurement as less is being blocked by the earth. Google on its maps shows altitudes at higher elevations but not at lower elevations, so maybe this is what is what is happening.

 

[Tighlines]

Being from Colorado, I can tell you that you can never be 'too high.'

 

[WasserGKuehlt]

There's a discrepancy of about 50ft between the readout on my 4CT and the Garmin Fenix (lower). Incidentally, the reading at home with my previous watch is exactly what the car is showing. As a final data point, I recall looking at the compass upon entering the Eisenhower Tunnel (from the East), and that showed 11k ft. CO DOT says the elevation of the Eastern entrance is 11,013. I'm inclined to say the car's altimeter is pretty accurate.

 

[mcdermottm]

Does the altitude read out vary by day at the same location? Or is it always 88 ft.?

 

[cityhpper]

Altitude readings seem quite accurate. I expect the car to have more data sources than map information and GNSS alone, as it also reports acurately negative hights - like when driving in tunnels hundreds of meters below sea level.

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