MySQL select coordinates within range

Question

I\'ve in my database 100 000 addresses (that is records).

Each one of them has its own coordinates (latitude and longitude).

Now, given the geo location of

Answer 1

My approach - and I am using it - is to think like a technician, I am happy with +/- 5%

This solution is not meant to control rockets, boats or a like, and only for distances below ~100km its just a solution like Fermi problem

So lets start for a pragmatic solution:

First: for many problems we can ignore that earth is not flat (distance <~100km) ,

The circumference of the earth is more or less 40000 km (more or less exactly for some reason)

A circle has exactly 360 deg.

So 1 km is: 360/40000 deg => 0.00278 deg

And then just select lat/long within this 0.003 per km, it will be something like where long > 42 - 0.003 and long < 42 + 0.003 - same for lat, where 42 is your lat/long as middpoint. The Database will use the indices.

the problem: you get a square as result not a circle (not real distance)

If you need the circle, script it after getting the results.

I just show the official toilette with in 2 km, so a square is ok, and the accuracy, too. The reason is, that there are streets and houses, so people can't walk directly ...

Edit: Technical / mathematical explain:

For very small triangles (one angle << 5 deg) you can ignore the use of trigonometry. So sin(5 deg) ~= 5/180*PI