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 -- The WA Macintosh User Group Mailing List -- Archives - <http://www.wamug.org.au/mailinglist/archives.shtml> Guidelines - <http://www.wamug.org.au/mailinglist/guidelines.shtml> Unsubscribe - <mailto:[email protected]>
