In article ,
says...
How can it fine-tune the GPS height without a reference MSL pressure at the point and time of observation and where does it get that from? How accurate is the reference MSL pressure? Precision aneroids are fairly thin on the ground, at least in this part of the world.


I would assume...

In order to get any sort of sensible reading from gps, samples have to
be taken over a period of time and averaged. This is not much good if
the altitude is changing during this timespan. With gps chips providing
no more than 2 samples /sec and, I imagine, quite a lot of samples being
required, that timespan could be as much as 30sec.

The barometer provides a very accurate reading of how much the altitude
has changed between each sample point and this is used to normalise each
gps sample point to the same altitude as the first sample point before
averaging and again after averaging to normalise the result to the last
sample point.


IOW, it is changes in pressure that matter. Not the actual pressure.

I assume, because I don't rightly know. I can't think of how else they
would do it but whatever they do does provide some pretty impressive
results compared to raw gps data.



--
Alan LeHun
Reply-to is valid. Add "BPSF" to subject: to bypass spam filters.

On Sunday, 13 July 2014 18:22:10 UTC+1, Tim wrote:
I came across an app (CPUZ for Android in the Google store) which I

wanted for another reason. I was rather surprised that there's a

barometer in my Samsung S3 giving hPa to one decimal place. I have no

idea how many phones have this sensor, but the app is free.



That's all well and good Tim but where are the obligatory two clothes brushes kept? Eh, answer that one?