On 2020-05-06 14:09, Graham Samuel via use-livecode wrote:
Bill, I think you are confirming that there is some mystery here.
There are a lot of apps that seem to get location, and measures
derived from location, almost completely right, whereas I am having
trouble doing so with what must be the same essential data.
How then to avoid either under- or over-estimating the trip distance?
Plenty of apps have done it but I just can’t see how, although I keep
tinkering with the parameters. Of course I can never forget that my
scripting might just be plain wrong, but so far my incremental method
hasn’t worked sufficiently well, in the sense that if run the app and
choose to walk in an exact straight line, I can compare a single
measure of distance from the starting point with my integral approach.
So far the result is not even close. As you say, intensive Internet
searches are called for.
I'm pretty sure that the data you are getting is precisely what all
other apps will get - we are just returning the location data as
provided by CoreLocation. The difference will be the analysis which
these apps are doing on the data to derive an accurate assessment of the
route taken I'd imagine. Indeed, it could be they also take into account
other senses (compass and accelerometer) to help - but I don't know that
for sure.
There are two functions which might help you with your endeavour:
mobileSetLocationHistoryLimit
mobileGetLocationHistory()
The details are in the docs, but basically the engine can collect and
keep a list of locations which you can collect periodically.
I suspect the way to think about this is not to think about it as an
incremental thing at all as any outliers will completely destroy the
accuracy. Instead imagine it as a 'curve-fitting' exercise (piece-wise
linear approximation is probably sufficient!) - i.e. taking sets of
(slightly) overlapping samples and derive a 'best-guess' path which fits
the data.
It is likely that some cleaning of the data would be needed first to
eliminate outliers also. e.g. You can compute speed needed to get
between individual points, if any given point is outside of a reasonable
range of 'current' speed with approximated acceleration/deceleration
taken into account then it should be discarded.
Doing a google search for "deriving a approximate path from gps data"
turns up quite a lot of literature on the subject, so this is definitely
something which has/is studied in depth...
Warmest Regards,
Mark.
--
Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps
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