Geocoding - accuracy required in GPS coordinates?

Question

My question in a nutshell: is there a correlation between the number of decimal places used in GPS coordinates and location accuracy?

I am currently working with the Android SDK, but I am sure that this question can be applied to many other geolocation SDKs. Basically, Android returns GPS coordinates up to 14 digits. In most situations, this seems redundant. Suppose I needed an accuracy of about 10 feet by 10 feet. How many decimal places do I really need to worry about? The case I'm looking for, I want to know if a person is north or south of a certain latitude - how many digits do I need to store in the database and how many digits do I need to compare?

Answer 1

In New York - this is a fairly representative latitude where people live - crossing a wide street with two lanes will take about 25 meters, and you will pass about 0.1 seconds of longitude.

If you represent locations as 40 ° 42'42.96 "N 73 ° 59'23.33" W, then 0.1 seconds means the difference between one side of the street or the other. Depending on how you count your “decimal places,” then it ddd:mm:ss.ssssshould be accurate enough for human purposes. If you look at decimal degrees, then ±ddd.fff'fff'ffffor each of the latitudes and longitudes it will be enough, and you will leave some error for your rounding error.

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Answer 2

, . - , GPS - .

With regard to the number of digits needed to specify feet: It depends on where you are. A degree of longitude at the equator is about 110 km, but a degree of longitude here in Portland (45°N) is about 78 km ¹. So (at 45 N) every ⁴⁄₁₀₀₀₀₀° is about 10 feet when walking east or west.

^{1 (cos (45 & deg;) & times; & times; 2π)/360 ≈ 78}