Fantastic Ray. What a wealth of knowledge you have.
Last Tuesday I was trying to find WA Toner Supplies in Osborne Park.
It was overcast, drizzling and high humidity. I had been there before
but was tired so relied on Maps. I went to the western side of the
freeway. You can that Whereis.com takes you there. got there
eventually after I stopped and had a cold shower and concentrated and
backtracked.
Stuart Breden
PO Box 132
Kalamunda WA 6926
Ph: (08) 9257 1577
Mbl: 0417 053 266
http://www.whitepages.com.au/busSearch.do?subscriberName=WA+Toner+Supplies&location=Osborne+Park+WA
On 11/06/2011, at 2:21 PM, Ray Forma wrote:
There are several altimeter apps for the iPhone.
The one I would choose would be the Sichtwerk one:
<http://www.sichtwerk.com/referenzen/altimeter/> (this site is in
German)
This simple app gives you your latitude and longitude in DMS
(degrees, minutes, and seconds), as well as your altitude in m (or
feet for the oldies).
You are therefore not dependant on electronic maps, which will only
download if you are within phone range. Take along a good, old-
fashioned, paper map and find where you are from the app's
coördinates. Useful in Australia where about 90% of the country is
out of phone range.
Nearly all of the various altimeter apps get their altimetric data
from gps readings. The app measures how long it takes a gps signal
to travel from the satellite to your iPhone. The satellite signal
includes the satellite's altitude, as well as its position. Assuming
a standard signal speed, the iphone can therefore calculate the
distance between the satellite and the phone. Using the distance and
positional data from several satellites allows your iPhone to
calculate your absolute altitude, as well as your latitude and
longitude.
This is great, but there is a problem. The temperature and density
of the air along the satellite signal's path affects the speed of
that signal. This introduces distance-from-satellite variations that
your iPhone has no way of correcting. Assuming the distance
variations are uniform, your latitude and longitude calculation will
not be much affected, but there can be ±15m variations in altitude
on normal days, and greater in very high-pressure or low-pressure
locations, and very cold or hot locations.
As with dedicated gps receiver altitude readings, take a reading at
a known altitude as often as possible, work out the variation, and
then apply the variation to your subsequent readings.
In my experience you should take known readings about every 3 hours
to make fairly reliable altitude reading corrections.
The Sichtwerk app can apparently also use data from the ASTER
satellite to improve its altimeter accuracy, but I'm not sure if it
uses the ASTER temperature data in conjunction with the gps data to
calculate altitude. If it works only from the ASTER satellite then
it would not be usable most of the time because there is only 1
ASTER satellite. I don't think ASTER data are in public domain, so
the app probably gets the aster data by data link; meaning that you
have to be in phone range.
I use my Swiss Army knife that has a built-in barometric altimeter
if I want more precise altimeter data, again calibrating the knife
every 3 hours. My knife gives me repeatable ±2m accuracy on any day
that is not too stormy. I have never seen my version of the knife in
Australian shops. I got mine in Switzerland.
On 11/06/2011, at 10:54 AM, Stuart Breden wrote:
I see that Altimeter is reviewed in the latest Macworld magazine
for June.
It was also reviewed the Macworld site in April. A more detailed
review and did not appear to be very accurate.
Is Altimeter the only application that measures altitude? Are
others ore accurate?
Stuart Breden
PO Box 132
Kalamunda WA 6926
Ph: (08) 9257 1577
Mbl: 0417 053 266
http://www.studiosixdigital.com/altimeter.html
http://www.macworld.com.au/app-guide/altimeter-28876/
Regards,
Ray Forma
Mob +61 (0) 428 596938
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