Garmin 18 Hgt Survey
The background to this experiment came from reading the excellent set of pages by David Wilson, especially his page Modeling of GPS vertical errors , where David describes the vertical errors of a number of GPS receivers. Using the same methodology, I wanted to measure the Garmin 18 LVC module with respect height errors. This meant recording for a 48 hour period, with a FIX every 2 seconds. To judge whether the GPS is correct, we need a reference that is the TRUE height that the GPS module was placed at. For this I used a Novatel AC12 and a process known as "post processing" that can give a 3D solution down to a few centimeters (the level of Earth tides). Taking the 48 Hour recording of the Garmin 18, I first of all converted the height reading (Mean Sea Level) to WGS84 datum by adding the given "geoidal separation" value. Now the Garmin height was to the same datum as the reference "True Height".