So they're blending the systems. That and out experience indicates that the phone systems should be treated as non-precision. Therefore of limited value and not preferred for rescue operations.
Is there a way to make the phone uses GPS only?
Yes, sort of. Typically there is a location based setting but it's under privacy, so some people turn that off for fear of google tracking them. Suggest that's a bad idea for hikers.
Some people go into their settings or use a homescreen widget to turn off their GPS radio in their phone. Suggest that's a bad idea for hikers.
GPS works by first getting almanac and ephemeris data, then zeroing in location by constant satellite updates. Cell phones, unlike dedicated GPS receivers that get almanac and ephemeris from the GPS constellation, employ aGPS, aka assisted GPS, and get the seed data from the internet. Suggest that before hikers leave the city, launch Google Maps or GPS Status, both of which are free, to get their GPS systems dialed up and running. I would recommend Google Maps so you can tell at a glance if your phone is showing your location properly, and to check the Android notification bar for a little satellite dish icon - it confirms that the GPS radio is on and tying to the phone operations.
GPS location quality varies by phone make and model. Some will get you within a city block while others are so accurate it's downright scary. Good way to check, use Google Maps with the satellite view of your location and see how well the on screen location indicator matches your obviously visible position. Now, go for a walk, see if it continues to maintain good accuracy.
I guess that these are more usage tips than anything, and so I don't know if it is useful (or even new to you info) for SAR ops.
Anyway, hope this helps!
PS on cell phone aGPS - once on GPS better phones will stay on GPS unless there is a signal loss, at which point they will automatically switch to tower triangulation in an attempt to maintain position information. As soon as the GPS signal is reacquired, it uses that exclusively and will iterate to maximum location accuracy for that unit.
If a hiker gets hurt, but has a good skyview, about a 120 degree cone in a perfect world, if they place their phone on dry surface and just leave it be, running something like GPS Status, that phone will eventually get almanac and ephemeris from the constellation and eventually get a good location. This too will vary by model and state of the last ephemeris table, but from reports in our forums, typically can take from a few minutes to a half hour.
The rule of thumb for a cell phone, the more visible sky, the higher the GPS accuracy.
