GPS Accuracy

[trags3]

I don't see much re Accuracy of iPhone or Android GPS posted recently.
When I can catch my breath I plan to do an experiment to see if the error is pretty much constant and in the same direction at 2 points within about 125 feet of each other.
I know the absolute accuracy of an iPhone GPS is several meters. I read somewhere that by using another GPS with better accuracy and bluetooth that the iPhone accuracy can be improved.
Does anyone have any experience with this approach? I need to get the accuracy of the measurements between 2 points to within a foot or so (no elevation difference).

Probably a dream, but.....
Tom

[bogs]

Last year they were talking about getting GPS on android down to a meter or so...
https://www.gpsworld.com/how-to-achieve ... n-android/

Recent changes in hardware and standards make one-meter accuracy possible, in some cases as soon as this year. The transcript of a talk given to Android developers earlier this year, this article gives a short overview of location in smartphones, introduces Wi-Fi round-trip time technology and standards, and then explains the Wi-Fi application programming interfaces.

...but for down to a foot, you'd probably need the signal the military is using (L2).

handheldgpspro.com
GPS signals are sent via two different frequencies which include L1 (for civilians) and L2 (for the military). While the L2 signal is considered to be the most powerful and accurate frequency, the civilian L1 is usually weak and altered, making it impossible for it to send accurate readings.

Due to this reason, the best accurate GPS devices have used supporting programs such as the DGPS (Differential GPS), WAAS and GLONASS to boost accuracy. Without wasting any time, let’s review some of the most accurate GPS devices available on the market today.

I won't bother going into research done on using Wifi and cell towers to narrow down someone's position, as I assume your already familiar with those.