What is Enable assist GPS?

[Freezetron]

Ok, im now a week long owner of my first time smartphone and Droid user and there is so much to learn about this sucker its amazing. I'm starting to get into tweaking and modifying the phone without rooting to enable better battery life and performance.

I dunno if there is a manual for this thing that I can read, but I do know that the GPS function sucks alot of power on these phones and one of the options is this "assist GPS" option in settings. What is it exactly and should I or not I enable it wether I have the GPS radio turned on or not?

 

[TwerpPoet]

Go ahead and leave it on. It won't do anything when you have the GPS itself turned off.

GPS can take a long time to figure out where you are initially. Things go much faster if it starts with a rough idea of where it is. With assisted GPS the phone looks at the nearby cellphone towers and gets that rough position.

 

[RETG]

Might save a few seconds since it serves to give a pretty darn good exact location of the phone. It also supplies the latest almanac information for all the satellites. By supplying this info, the phone does not have to learn the almanac information, which might take up to 30 seconds. The phone still needs to load the latest Ephemeris data from each satellite. (Almanac info is common between all sats and gives the location of all sats. Ephemeris data is exact for each sat and each sat sends out its own Ephemeris data.)

If you live or work in an area with large (tall) buildings, it also helps to give a better and correct fix. Tall building are noted to not only block sat signals, but sat signals can bounce off objects (glass for one), which can give you an inaccurate location (not by much, but still not as accurate as a direct signal).

Another benefit is it can cut down power to the actual GPS receiver since it can rely on the cell phone tower triangulation.

 

[takeshi]

aGPS is not triangulation. That's a common misconception for some reason. All it does it fetch Ephemeris data to obtain a faster initial fix.

 

[TwerpPoet]

aGPS is not triangulation. That's a common misconception for some reason. All it does it fetch Ephemeris data to obtain a faster initial fix.

I'm not sure exactly what components of Assisted GPS the phone uses, but here is an article that describes what falls under the description, a la Wikipedia.

Assisted GPS - Wikipedia, the free encyclopedia

My answer turns out to be incomplete. In some instances of marginal GPS signal it looks like Assisted GPS may indeed cause extra battery drain. It may use a remote server to calculate position.

If the phone uses that ability, of course. Does anyone know for sure exactly what Android's implementation of Assisted GPS does? And as a confidence builder it would be nice to have the reference.