location based

[RDP1974 40]

hi,

do you know a good source of algotithms for location based purposes?

example calc the distance between two coordinates, etc.

thank you

[FPiette 384]

If you are talking about  geographic coordinates, look at the haversine formula.

function HaversineDist(
    Lat1 : Extended;   // Latitude  of point 1 in degrees
    Lng1 : Extended;   // Longitude of point 1 in degrees
    Lat2 : Extended;   // Latitude  of point 2 in degrees
    Lng2 : Extended)   // Longitude of point 2 in degrees
    : Extended;        // Distance in meters
var
    Dx, Dy, Dz : Extended;
const
    Diameter = 2 * 6372.8 * 1000;   // Meters
begin
    Lng1    := DegToRad(Lng1 - Lng2);
    Lat1    := DegToRad(Lat1);
    Lat2    := DegToRad(Lat2);

    Dz     := Sin(Lat1) - Sin(Lat2);
    Dx     := Cos(Lng1) * Cos(Lat1) - Cos(Lat2);
    Dy     := Sin(Lng1) * Cos(Lat1);
    Result := ArcSin(Sqrt(sqr(Dx) + Sqr(Dy) + Sqr(Dz)) / 2) * Diameter;
end;

 

[RDP1974 40]

thank you

if I have time will try to implement a general purpose KNN R-Tree algorithm in pascal

 

[FPiette 384]

22 minutes ago, RDP1974 said:

thank you

if I have time will try to implement a general purpose KNN R-Tree algorithm in pascal

What is the relation with your initial question and my answer ?

[RDP1974 40]

well, calculate the distance between two points is needed

 

[FPiette 384]

In which space are your points? The formula and code I gave is for computing the distance between two points of given by their geographic coordinates (On a sphere which is the earth in my code). The distance is computed on a great-circle.

The formula for two points located on a plane is different and simpler.