Barometric Altimeter, does it matter?

Google Maps has heights values for every point on the map. The topo maps also have heights for each point on the map. So with GPS positions theoretically the Garmin software can extract the corresponding heights from the map and no barometer needed. But are some situations when barometer can be used:

a - the height differences provided by barometer can be used for checking purposes outdoors (the heights from the maps can be checked against the heights provided by barometer).

b - the sudden drops in atmospheric pressure reflect weather change (storms)

c - some activities indoors needs barometer (floors counting, stair climbing or even indoors positioning).

The most problems and conflicts appear with the "calibration" phase of barometer.

For example, in a point situated on a sea shore (0m at sea level) the atmospheric pressure is 1013mb, but changes in time (because of weather) with +/- 20mb. Knowing that 1mb means about 10m in height, a variation of +20mb means a height of -200m "above" sea level. It is a non sense so the barometer need a "calibration" (is not a calibration is an initiation) and need form the user the correct 0 value. From now on the variations in pressure (measured by barometer) are added to this initial value. If instead of the correct 0 value, the GPS give us the wrong +50m (as the initial value) the barometer will provide (for each point) heights that are in conflict with the heights from the map. The software is not always smart enough to decide what is the good alternative.

/r/Garmin Thread