CODEWITHSUNDEEP
mysqlgeolocationdistance
Marreone
Marreone

Reputation: 117

Distance between two points. East-west + North-south

I need to calculate the distance between two points, but not in the regular way. I need to know 'the east to west distance' + 'the north to south distance'. I guess this is more simple then the regular 'as the crow flies' calculation but i still can't figure out how to do it.

I want to do this using a MySQL query and preferably have the result returned in km. One of the points will be a constant in the query and the other point is a point from the DB so something like SELECT abs(longitude-39.12345)...+abs(latitude... AS Distance FROM shops WHERE shopname='Bingo'.

Thanks in advance!

Upvotes: 0

Views: 19604

Answers (5)

captaintom
captaintom

Reputation: 961

You can determine the distance between any two geocode points using the Great-Circle Distance. Here is another decent article on the subject.

The following is an example in C# which shows how to do this:

var earth_radius = Constants.EarthRadius; // 6377.8 km

var dLat = ToRadians(fromLatitude - toLatitude);
var dLon = ToRadians(fromLongitude - toLongitude);

var a = 
    Math.Sin(dLat / 2) * 
    Math.Sin(dLat / 2) +
    Math.Cos(ToRadians(fromLatitude)) *
    Math.Cos(ToRadians(toLatitude)) *
    Math.Sin(dLon / 2) * 
    Math.Sin(dLon / 2);

var c = 2 * Math.Asin(Math.Min(1, Math.Sqrt(a)));

var distanceInKilometers = earth_radius * c;

Upvotes: 0

Cyril Barnert
Cyril Barnert

Reputation: 1

The east-west difference between two points at different latitudes is a distinct number in degrees of longitude, but converting this to miles is problematic because the miles per degree vary according to the latitude. For example, Los Angles and New York City are 44.3 degrees of longitude apart, but converting this to miles would result in a larger number at LA's latitude than at NYC's latitude, since latitude lines are longest at the equator and shrink to zero at the poles.

A reasonable convention would be to count the E-W distance as the average of the two distances calculated at the two latitudes.

Upvotes: 0

ChrisW
ChrisW

Reputation: 56083

The north-to-south distance is proportional to the difference in the latitudes. It's about 1 nautical mile per minute of arc (the circumference of the earth is about 21600 nautical miles).

The east-to-west distance is proportional to the difference in the longitudes, but it also varies with the latitude (e.g. it's zero at the poles): I think it's proportional to the cosine of latitude.

Upvotes: 4

John Gordon
John Gordon

Reputation: 2704

Your answer depends on the accuracy required in your answer. If you don't need an answer more accurate than a spherical earth model, you can use a solution similar to the one given by Captain Tom. If you require more accuracy, you'll need to assume the earth is an oblate spheroid. See http://en.wikipedia.org/wiki/Vincenty%27s_formulae for a couple of solutions.

Upvotes: 0

Sushisource
Sushisource

Reputation: 611

Use simple trig. The normal "as the crow flies" distance is the hypotenuse of the right triangle formed with the two points you have in mind at either ends of the hypotenuse.

Just look at this http://en.wikipedia.org/wiki/Hypotenuse and the solution should become clear.

Upvotes: -2

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