# How to know person is inside or outside of given pairs of lat long.

Hardik Trivedi
Ranch Hand
Posts: 252
Hi all,

I am stuck up at one problem. I have few pairs of lat long which is creating closed boundary/fence on a map. Now I want to know whether person is inside that fence or not ?
How can I know that ?

Is there any api available or any algorithm is there or not ?

Peter Johnson
author
Bartender
Posts: 5856
7
You would have to first get the lat/long of the person's location. After that it is simple arithmetic.

Hardik Trivedi
Ranch Hand
Posts: 252
Peter Johnson wrote:You would have to first get the lat/long of the person's location. After that it is simple arithmetic.

Yea I have person's current location. I would like to know about the algorithm

Tim Moores
Bartender
Posts: 3128
50

Peter Johnson
author
Bartender
Posts: 5856
7
Hardik Trivedi wrote:Yea I have person's current location. I would like to know about the algorithm

You're kidding, right??? Have you tried visualizing the situation using example long/lats for the box, and log/lat for a user who is inside and not inside the box? Draw it out on a piece of paper if you need to. Or take a simpler case with a simple graph using X and Y coordinates using vertical and horizontal lines and the person being a point inside or outside the box. Of course, this ignores the possibility that the box encompasses either the north or the south pole, then the algorithm gets more complex.

Paul Clapham
Sheriff
Posts: 21554
33
I think that choosing the word "box" was unfortunate, as it strongly suggests a rectangle. However the original post said

I have few pairs of lat long which is creating closed boundary/fence on a map.

Note that "few" is not necessarily "two". So there's some kind of polygon involved but it's not necessarily a rectangle.

Peter Johnson
author
Bartender
Posts: 5856
7
The title says "given pairs of lat long", so I assumed that Hardik had two longitudes and two latitudes, which then described a rectangle (or at least, as close to a rectangle that you can be on a sphere). Of course, if that is not what Hardik wanted, then I guess my comments don't really help!