This for those that are new toGPS.

I'm assuming most know that the US military controls GPSsignals.  Think about it.  The public being able to put something in a1ft diameter target.

With that in mind, remember that you will never have anaccurate reading even with a lot of signal lock.  Your location will always be movingand can move a long way.  I've attached ascreenshot of a minute "flight" that never left the kitchen table.  11 satellites and 64ft of total distancetraveled.

This is why you need to have a good open spaceto set your home location and an extra set of eyes if you can.  If you pushthe home button it could land in the tree in your front yard, however unlikely,but the possibility exists.

To be fair you were indoors and no matter how many GPS sats you were locked on errors are likely.  There are plenty of conspiracy theories alive out there but I disagree that the military or government purposely built error factor into the GPS system. Our GPS system is not extremely precise due to many factors and equipment, weapons, and navigational systems (yes even military) has error factors.
The main cause for error is based on multipath error.   
Here's some GPS Multipath Error information for those who are interested.  For those who would rather focus on conspiracies, feel free to ignore the following.
1) No GPS receiver is designed to be used indoors at any time and any operation you get is gratituous and likely to have large errors.
2) Multipath results when the direct path to your receiver is blocked (by  your body,  your house,  roof,  trees,  mountains,  buildings,  etc) and the signal from the satellite is REFLECTED by some object.  The reflecting surface may be:  buildings,  mountains,  the ground,  or any object that happens to be a radio reflector at 1.6Ghz.
3) Multipath are radio signals which have traveled FURTHER to get to your receiver than they should have.  This can result in your GPS miscalculating its position because the signals may have traveled from feet to miles further to get to you than a direct line of sight signal path would have been.
4) Multipath can cause longer term "stable" errors or it can cause your position to wander at varying rates (even thousands of miles per hour if your GPS could follow such speeds).  Sometimes GPS wanderings caused by multipath can cause your GPS to "jump" from one position to another as the multipath signal "comes and goes" and causes your GPS to jump from using one group of erroneous signals to another. These "jumps" can add substantial distances to the tracklog measurements in some GPS receivers.

So I was going on information about 2 decades old.   I just figured the govt wouldn't have change by now. I was thinking about the selective availability from the 90s. But the current govt GPS site corrects my thoughts about how it works now. But still be cautious out there, the errors still can place your position off by a fairly good distance.

http://www.gps.gov/systems/gps/performance/accuracy/
Selective Availability (SA)?
During the 1990s, GPS employed a feature called Selective Availability that degraded civilian accuracy on a global basis.

In May 2000, at the direction of President Bill Clinton, the U.S. government ended its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.

The United States has no intent to ever use SA again.

Also keep in mind that it is not just the GPS satellites that are being used for the Phantom 3, it is also the Russian GLONASS satellites. Without a clear view into the skies (because of roofs or clouds) there will always be issues, and now there is also any discrepancies between the two systems. GPS is great, but not perfect and you should always keep that in mind when relying heavily on the satellites.

Is anyone using RTH consistently when it's time to bring their bird home? The error range, even with the dual navigation satellites, has me scared that I'd put the drone in a bush, on a roof, or hit my fence. I've got about 15 flights so far and have never once hit the RTH button due to me being afraid of the accuracy. I should probably test it at some point though...

Davememex..I use my bird in tight quartrers a lot.   Ten times out of ten,after my (RTH) has kicked in,I wait until it's about 50' from me then toggle the s1(FullTravel) back and forth.As soon as you see the rear leds return to solid green,the bird is yours again.Alot of times I find hat it's safer for me to take control  again....I am usually a lot closer to the bird than home point....I would recommend trying it an open field...I do believe you'll like it.         

coherent Posted at 2015-5-5 23:48
To be fair you were indoors and no matter how many GPS sats you were locked on errors are likely.  T ...

No it is true the gov does control GPS and can change it at will. The use indoor actually should be better as placement is based on other sensor location. What is   wrong is the actual map moves from GPS signals.

coherent Posted at 2015-5-5 23:48
To be fair you were indoors and no matter how many GPS sats you were locked on errors are likely.  T ...

No it is true the gov does control GPS and can change it at will. The use indoor actually should be better as placement is based on other sensor location. What is   wrong is the actual map moves from GPS signals.

coherent Posted at 2015-5-5 23:48
To be fair you were indoors and no matter how many GPS sats you were locked on errors are likely.  T ...

No it is true the gov does control GPS and can change it at will. The use indoor actually should be better as placement is based on other sensor location. What is   wrong is the actual map moves from GPS signals.

Two Snakes Posted at 2015-5-6 00:26
So I was going on information about 2 decades old.   I just figured the govt wouldn't have  ...

That is correct. Commercial and private aviation now use GPS every day. I regularly fly GPS instrument approaches in my airplane and it will guide me through the clouds with 100% reliability and put me right over the end of the runway. Thousands of lives every day depend on it. With that confidence I don't mind depending on GPS with my P3.

Use indoors will not be better. The sat signals are already low in power by the time they reach your antenna. Being indoors provides further attenuation of the sat signals.