How can I calibrate my elevation?

I noticed this problem seems to have started in the last month or so I think. I usually start my tracks at a place that is around 8m above sea level. When I start the track logging the elevation is always negative by a long way, e.g. -30m or -28m. This affects the elevation across the whole track as it's always under reading by that amount. Is there any way I can calibrate Oruxmaps and my gps to show a more realistic elevation? I don't know if I changed a setting in Oruxmaps to cause this or if something else is wrong but I've looked everywhere to try fix this.

I use a Holux gpslim 236 (which is quite accurate) with a Galaxy S2.

cyberdude wrote:I noticed this problem seems to have started in the last month or so I think. I usually start my tracks at a place that is around 8m above sea level. When I start the track logging the elevation is always negative by a long way, e.g. -30m or -28m. This affects the elevation across the whole track as it's always under reading by that amount. Is there any way I can calibrate Oruxmaps and my gps to show a more realistic elevation? I don't know if I changed a setting in Oruxmaps to cause this or if something else is wrong but I've looked everywhere to try fix this.

I use a Holux gpslim 236 (which is quite accurate) with a Galaxy S2.

Hi;

GPS settings, 'NMEA, altitude correction'
on-->the altitude from the gps will be corrected with the geoid--ellipsoid altitude difference.
off-->OruxMaps will use the altitude provided by the GPS directly.

Yuo can calculate de geoid--ellipsoid altitude here-->http://www.unavco.org/community_science/science-support/geoid/geoid.html

There is a deprecated setting: 'Altitude correction' --> set to zero.

orux

Thanks for replying.

GPS settings, 'NMEA, altitude correction'
on-->the altitude from the gps will be corrected with the geoid--ellipsoid altitude difference.

I already have those setting but I still get the wrong elevation.

I calculated the geoid alt and got the following but am not sure what I'm supposed to do with the information.
Latitude N = 37° x' 35.81" N
Longitude E = 8° x' 6.73" E
GPS ellipsoidal height = -23 (meters)
Geoid height = 43.043 (meters)
Orthometric height (height above mean sea level) = -66.043 (meters)
(note: orthometric Height = GPS ellipsoidal height - geoid height)

cyberdude wrote:Thanks for replying.

GPS settings, 'NMEA, altitude correction'
on-->the altitude from the gps will be corrected with the geoid--ellipsoid altitude difference.

Hi,

Tell me the OruxMaps altitude values (at the same point) with that setting 'on' and 'off'.

orux

Just an update. I now have it working correctly. It was a user error in how I was using Oruxmaps. I was using an external BT GPS receiver along with an BT GPS provider app, Blue GPS, and was at the same time starting the gps using the "Start ext GPS" option which seems to affect and produce an incorrect altitude reading.

Now I just use the "start ext GPS" option directly with my BT GPS device without the Blue GPS app and it all works fine. Also, the NMEA altitude correction needs to be turned off.