Altimeter calibration

[tomk62]

I know I can use other devices to get the same info. I just want the instruments on my 2024 Jeep to be reasonably accurate. @JeepCares is this a known issue?

My iPhone says I am at 0 ft elevation (correct):

My Jeep says I am at -104 ft (obviously incorrect):

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[Riverjeep]

I have not but I'll try it on my errands this morning

I just checked my iPhone altitude with the compass app along with offroad pages on my 2024 Rubicon. My phones was 10-15 feet too high and my Jeep was 100-115 feet too high which is very similar to yours. This is absolutely atrocious, now i want mine corrected also!

 

[bugnuker]

My 2024 is also constantly about 100 feet off when compared to other devices, Garmin, phones, etc

GPS is always calculated on the device. The device receives signals from satellites and then calculates the data/position locally on the device. This means they have somehow messed up the calculations in the software. I would hope they could fix this with an over the air software update.

 

[GtX]

Also I may have no idea what I'm talking about.

But are simultaneously confident you have a problem. Hmm.

Elevation accuracy of GPS is generally 1.5x horizonal, or about 75 feet, under near perfect conditions at and alpha of 0.05. Buildings, bridges, trees, the vehicle make for not perfect conditions. You're phone is not perfect.

It's easy to convince ourselves our GPS is more accurate that it is thanks to maps and algorithms that determine we are on the road even if the raw signal is 100+ feet off the road. You'd be happy is the software just told you your elevation was the elevation of the point on the map it guesses you're at in the moment.

 

[Jtphoto]

My 2022 with Nav reads off the satellites and produces the same measurements as my phone apps and GPS

 

[Bobby Hank]

Mine says I’m -70’ below sea-level at home. Florida panhandle.

 

[Ratbert]

Also I shouldn't have been negative without a lot of engine trouble 8)

Not necessarily. Some parts of Death Valley are well over 200 feet below sea level.

I'd expect GPS to be vertically accurate to about 45 feet. It's weird that it's that far off, but we're a couple thousand feet higher than Denver, so 80-ish feet is noise here.

 

[Riverjeep]

But are simultaneously confident you have a problem. Hmm.

Elevation accuracy of GPS is generally 1.5x horizonal, or about 75 feet, under near perfect conditions at and alpha of 0.05. Buildings, bridges, trees, the vehicle make for not perfect conditions. You're phone is not perfect.

It's easy to convince ourselves our GPS is more accurate that it is thanks to maps and algorithms that determine we are on the road even if the raw signal is 100+ feet off the road. You'd be happy is the software just told you your elevation was the elevation of the point on the map it guesses you're at in the moment.

Ah Grasshopper, I see you have discovered Google! ?

 

[Mguy]

I would have guessed it was triangulated from satellite fixes just like I assume your lat-long is established. I assume that's how your phone would do it. Also I may have no idea what I'm talking about.

I thought GPS devices figure out Doppler shifts from satellite data, but then I thought I was wrong. But people frequently say to me "what were you thinking?"

 

[Jeffy56]

As I mentioned earlier, "GPS Test" is a cool program. The attached screenshots are very telltale. 12 foot accuracy?!? Even if very opportunistic, Wow! 3 MPH screenshot is me walking quickly. Pretty sensitive. Some phones are better than others, this one is a S21 FE 5G. The earlier posts at 29K ft were in Airplane mode, on an airplane! Elevation readings on land are within 15 feet of posted landmarks.

 

[Barchetta]

@JeepCares
Why isn’t there a compass app on the new 12.3 display? My wife’s Telluride can display 3 different compass images. There should definitely be an app we can add to any panel if we want to display a proper compass. We are often off road with no cell service but our Wrangler will have GPS. I know we can get all the data if we look across multiple screens/locations. But lack of a proper compass display is an obvious omission on an off road/overlanding vehicle.

Recommendation
Make a displayable compass app similar to the iPhone version. Make sure it has altitude and lat long too. My dream app would also display the city AND county we’re currently in. Roll it out as a software update for current Jeeps. It’s ridiculous that a Kia has 3 compass choices to display but a Wrangler doesn’t have one at all short of a coarse “SW” cardinal direction. It should be to the degree. A really cool Easter egg idea…it should display all the headings in whole digits (e.g. 250 deg) EXCEPT for 194 which should be displayed as “Since 194.1” with some Jeep theme splash image.

 

[RicRecon]

The GPS satellites constellation is in orbit relative to a mathematical representation of the earth surface. The satellites broadcast time across multiple frequencies and the Jeep is likely a single frequency receiver which must be receiving quality (unobstructed) readings from a minimum of 5 satellites to adequately calculate an elevation on the surface of that mathematical model. This is known as the ellipsoid height. If you want a more accurate elevation to actual ground, you would need to be able to upload an orthometric correction which varies from the model depending on where you are located on the earth. This is known as the orthometric height. In my area, the difference between ellipsoid and orthometric height is about 3 feet but it can vary much more than that.

face your Jeep generally to the south sky which is predominantly where the GPS satellites are located with as clear views to the sky at least 15 degrees above the horizon for the best coverage. The more satellites you’re reading, the more accurate it will be. But still not perfect in terms of ground elevation. If you are within 20-30 feet, you are doing good.

 

[Chupacabra]

Always thought GPS-based altitude was not as accurate as lat/long. Da Google says it can be within +/- 75 feet. Garmin says theirs is only accurate to +/- 400 feet! I think what you get out of the Jeep system is as good as it's going to get.

 

[tomk62]

The GPS satellites constellation is in orbit relative to a mathematical representation of the earth surface. The satellites broadcast time across multiple frequencies and the Jeep is likely a single frequency receiver which must be receiving quality (unobstructed) readings from a minimum of 5 satellites to adequately calculate an elevation on the surface of that mathematical model. This is known as the ellipsoid height. If you want a more accurate elevation to actual ground, you would need to be able to upload an orthometric correction which varies from the model depending on where you are located on the earth. This is known as the orthometric height. In my area, the difference between ellipsoid and orthometric height is about 3 feet but it can vary much more than that.

face your Jeep generally to the south sky which is predominantly where the GPS satellites are located with as clear views to the sky at least 15 degrees above the horizon for the best coverage. The more satellites you’re reading, the more accurate it will be. But still not perfect in terms of ground elevation. If you are within 20-30 feet, you are doing good.

Why can my iPhone be dead on but my Jeep in the same location can be off by 100+ feet? Can't really have a much better unobstructed view of the sky than when sitting on Folly beach at essentially sea level.

 

[Sidewalk]

The only time I am this stressed about elevation is when I'm listening ATIS for my barometer setting.

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