GPSed Blog

Mobile GPS Tracking Service

April 22nd, 2009 by odonata

Many users are contacting us with the question why an altitude value is negative for their tracks. In the most cases this is a normal situation and not an error!

This happens because GPS receiver obtains an altitude value comparative to sea level but not to a ground level. At some places of the Earth ground level is lower than sea level. The lowest point of the surface of the Earth on dry land is the Dead Sea in Israel.  It is 422 meters (1,385 ft) below sea level.

But sometimes GPS receiver itself can wrongly obtain negative value of altitude comparative to sea level.  For more accurate fixing position in 3D mode at least 4 satellites required. That’s why when connection to satellites is bad, GPS receiver can work in 2D mode obtaining wrong value of altitude (elevation).  To fix it find open territory and wait for a least 4 satellites found.  Or purchase high-end GPS receiver.

As usual, please feel free to contact us if you need any assistance with our software.

Kind  regards,
GPSed Team

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16 Responses to “Why “altitude” can be negative?”

JackD Says:

I get exactly the correct altitude but with a “-” in front of it… nothing to do with 3D/4 Sats…

Valery Says:

JackD »
Please specify your platform, device and application version you are using.

ndelregno Says:

My Blackberry Storm (9530) shows negative altitude. For example on a recent hike in a Dallas suburb (well above sea level) I show the following altitudes: Average -397.7, Max -318.2. At the time I had 10 to 11 satellites, so 2D mode shouldn’t have been an issue.

Valery Says:

Please send your tracks with negative altitude (.gpsed or .GPX files) to feedback@gpsed.com

We will analyze them and try to find reasons of such problems and possible solution.

Alex Says:

Actually there’s one more reason why altitude can be shown is negative. There’s a good article covering this issue: http://www.esri.com/news/arcuser/0703/geoid1of3.html - for those who care :)

Alex Says:

And yes, if you want an exact altitude - go for barometric altimeter. Some decent GPS receivers are equipped with this stuff.

Travis Says:

I also get negative altitudes. I know I am above sea level and usually have 10 or 12 satellites. BlackBerry Storm 9530.

Big Josh Says:

I think GPSed has issues…it is the ONLY GOS program I am using on my 9530 that has an issue with negative integer elevations.

My Garmin 60Csx, Garmin 750 and my Garmin Legend ALL show the correct altitude.

Everytrail shows correct altitude, why can’t you?

Menno Versteeg Says:

http://www.gpsed.com/track/5098132665583333185

I live at sea level and the altitude is -46m
clear sky and no high buildings and more than 7 satellites

It’s only on GPSED and my BOLD 9000

On the plane the max was about 6450m (need to be 9000m)
funny that the file:
http://www.gpsed.com/track/5098132662661420202
gives an altitude of -33m

BorderBob Says:

My 9530 shows negative numbers on several GPS applications. Wierder still, the higher you go the lower the elevation number.

b.b.

ndelregno Says:

Seems to be an issue with the GPSed app on the blackberries. Our troop had two 10-mile hikes this weekend which I recorded with my Garmin Etrex Vista HCx and the altitude appears positive and correct.

Valery Says:

It seems like some BlackBerry models (e.g. BlackBerry Storm) has a bug in early OS versions, which cause altitude value to be negative.

We are working for some workaround for this issue. As for now you can try to update your BlackBerry OS to the latest version. Please let me know if issue persists.

Mateo Says:

2.

I was at FL270 the other day and it was showing me at around a max of 111′, average for the route -7500. Looks like a datum plane is in the wrong place. Here’s the route.

http://www.gpsed.com/track/448082143967244880

(Blackberry 8320 Curve)

Daniel Says:

The issue persists on my BB Storm 9500 with the new offical software (Version 4.7.0.141 Vodafone Germany), that i installed on saturday.

I have a suggestion to solve the problem.
If you build in an option, that multiplies the altitute with -1 (eg -300 x -1 = 300) it is solved.

James Says:

Are you suggesting that most of us live near the dead sea???

I suggest you have a bug to fix

zylbj Says:

http://gpsed.com/track/499853472388572053

the same problem。
the mountaintop is -679M.but on the map of the mountain is 660M。
http://lh5.ggpht.com/_JPfo-KKL5Gs/SipuOtK8BdI/AAAAAAAAAN8/wIP75HvBeHU/s400/gaodu.jpg
BB8800,GPSed 1.3