Altimeter

Hello, I think you will find its a figure provided by the GPS. These are notoriously bad at getting altitude correct based on my experience. You can only use the figure provided as a guide..i.e plus or minus x metres.

Cheers Greg

Seems about right according to info available.

"The general rule of the thumb is that vertical error is three times the horizontal error. If a decent signal reception is available, a modern GPS receiver should be able to give elevation data accurate to a range of 10 to 20 meters (35 to 70 feet) post correction."

Cheers
Jim

John,

Just wondering if you are using your tab 8 with your mobile data turned off?

It is generally computer corrected very 20mins when in phone service.

If direct of the GPS you may well be getting as best your device can supply.




Regards

TrevorDavid

John, apart from being the least accurate of the measurements, height, or Z is the least understood parameter.

A raw GPS reading does not show height above sea level, it can't because the GPS system has no idea what sea level is. If you are using WGS 84, it will give you height above that model of the earth and sea level which on average across the whole world is the same as sea level. But in reality, can be a few meters or more different because the model earth shape is not the same as the real world's shape.

So, like your experience, the GPS can show that you are several m below WGS84 sea level, but still above the real sea level.

I am not sure how EO handles this, but in Memory Map, you can download the actual date for height above sea level across the world. You can either display that, or GPS height or both. They are rarely the same thing. The height above sea level is downloaded from satellite Dopler height data from NASA. I think Oziexplorer can do the same. It took me ages to figure out why Memory map showed both and they were different values.

If EO can display height above sea level you should use that, otherwise, accept that your displayed GPS height can be different to your height above sea level depending on where you are.

When you are away from the sea, you rarely notice this, unless you are a sign showing altitude above sea level, but if it says 1355m and your GPS shows 1345m you tend to dismiss the difference.

Ausgoid 09 goes some way to address this if it is supported.

Then, of course, there is the actual tide which could be higher or lower than the average.

John.
While the signals from satellites are read by your gps until they vary in distance from each satellite across the face of the earth, the gps algorithm determines your position, sort of, BUT it is far less accurate to determine the difference of your feet in relation to your head. Presumably it is above the feet, BUT the time shift distance between your feet and head is so small it is almost negligible and the signal is the same time length. Until there is a reasonable distance change in Z, there is no real signal time difference to be detected unlike a few steps forward or back.

John, to get an accurate altitude measurement you need at least 2 satellites high in the sky and idealy separated by at least 45 degrees. Satellites nearer the horizon give more accurate positions but more inaccurate altitude.
Cheers Andrew

Don't some apps estimate altitude using a combination of the barometer, gps (x,y)/ map position and gps (z)? Incidently, won't the next generation of gps used in autonomous vehicles be using differential gps so accuracy will be cm?

Thanks to everyone who made comments. Seems I cant do much about the altitude in this unit, and it really doesnt matter that much anyway. Just as well I can breathe under the sand at the beach!!!!!.
I also use my iphone8 with motion X GPS, when I am out and about, which has other benefits over ExploreOz.
Anyway, all is well and I am grounded.

In Oziexplorer you need to select the option:
'Adjust the altitude for Geoid separation'
The Samsung GPS chips are known to be poor and slow.

Hi...I m going thru the manual and its says it needs a control signal or some sort of switch connected to an ignition source. What are you guys using for a ignition source? Do you think an Add-A-Fuse to a reliable source would be sufficient enough?