I have difficulties in decoding the nRF9160 GPS output data. I know that nRF9160 reports its GPS data in NMEA GPGGA format, however, I am wondering why the last number which is the height of geoid (mean sea level) above WGS84 ellipsoid is missing.
I am getting this data from nRF9160:
$GPGGA,123519,4807.038,N,01131.000,E,1,07,1.93,606.57,M,0,,*31
and based on my searches, the data is coded as follow:
123519 Fix taken time
4807.038,N Latitude
01131.000,E Longitude
1 Fix quality: 0 = invalid
07 Number of satellites being tracked
1.93 Horizontal dilution of position
606.57,M Altitude, Meters, above mean sea level
*31 the checksum data, always begins with *
But, after "606.57,M" there should be another number in meter unit which tells you the height of geoid (mean sea level) above WGS84 ellipsoid but it is missing from nRF9160 output data.
For instance, correct data is like this:
$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
in which, "46.9,M" shows the height of geoid (mean sea level) above WGS84 ellipsoid. I guess this is a non-standard implementation and I found that some non-standard implementations report altitude with respect to the ellipsoid rather than geoid altitude. Some units do not report negative altitudes at all. This is the only sentence that reports altitude.
I am wondering if nRF9160 is reporting altitude in ellipsoid rather than geoid or not reporting it at all? Are there any helpful resources that explain nRF9160 GPS output data?
