One of the most exciting features of BasicAirData GPS Logger is the automatic correction of the GPS altitude error. The main altitude measurement errors are due to the difference between the Earth mean Ellipsoid (the zero-reference of the GPS) and the real Earth Geoid. That difference depends on Latitude and Longitude.
Many models describe that Geoid; GPS Logger uses the NGA/NASA EGM96, N=M=360 Earth Gravitational Model, defined by the binary geoid height file hosted on the National Geospatial-Intelligence Agency site, to calculate the right altitudes over the sea level.
When The EGM96 Automatic Altitude Correction is selected for the first time into the Settings Screen, the app downloads the geoid Heights binary file from the NGA/NASA website. The size of that file is about 2 MB.
This is a one-time operation: once the EGM file has been downloaded, you can freely use, enable and disable the automatic Altitude Correction without any Internet connection.
However, in some cases, you would have the possibility to set up the EGM correction without connecting to NGA/NASA website. For example when:
- You are using a smartphone with Android 4.x (the automatic download of the EGM grid fails because this version of Android doesn’t implement the HTTPS feature)
- You already downloaded the EGM file, and you merely want to use it within the app
- You installed GPS Logger on a phone that, for any reason, cannot reaches the NGA website
- You want to use the automatic correction with a different data set
In these cases, you can load the EGM file into GPS Logger by following these simple steps:
- Start GPS Logger and record a track. Then go on the Tracklist tab and export the track. The App could ask the permission to access the device storage: in case, please click Yes
- If you don’t have it yet, download the
WW15MGH.DACEGM file using your Personal Computer
- Connect your Android Device to your Personal Computer using a USB Cable
- Open the File Manager and copy the
WW15MGH.DACEGM file to the folder
/GPSLogger/AppData/of your Android device memory. The AppData folder has been created by GPS Logger when you exported the track at step 1
- Open GPS Logger, go to Settings and enable the EGM Automatic Altitude Correction.
Please note that, on android 6+, the storage permission must be granted to GPS Logger (at step 1) to load the EGM file