Lat Long Distance Calculations

[puforee]

In MS Access I want to calculate the distance between two Lat Long points. I was told there is a FAQ about this but I cannot find it.

I would like to mechanize it by having a From Lat field and Long fields and a To Lat field and Long fields. When these are populated I would like to have a calculation field show the distance between the From and the To points. I would like this to be fairly accurate. It should include the entire world so + and - would have to be part of the equation. I already have a table of 1000's of lattitude and longitudes for various cities in the world.

Thanks,

 

[PHV]

Have a look here:

http://www.movable-type.co.uk/scripts/latlong.html

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[puforee]

Very interesting but I am not sure how to translate the formulas to VB for Applications.

Maybe I am bitting off more than I can chew.

Thanks for the link,

 

[SkipVought]

Well you take a stab at coding it.

Then you run the code and evaluate the results.

THen you post back if you have specific questions.

Skip,

_{Just traded in my old subtlety...
for a NUANCE!}

 

[Bong]

First, I don't do much with Acess but the functionality you want should be basic VBA.
Second, how accurate does it have to be? Is a spherical Earth (mean radius = 6371 km) sufficient?

You basically need to do 4 things (for the spherical case):
1 convert hours,minutes,seconds to decimal degrees
2 convert a lat/long pair (in dec. degrees) to x,y,z
3 compute the included angle (in radians) between 2 xyz's
4 compute the distance between points on the Earth's surface that correspond to the included angle.

Function hms2deg(h, m, s)
    h = h + m / 60# + s / 3600#
    hms2deg = 360# * h / 24#
End Function
Function latlon2xyz(lat, lon)
    'lat,lon in dec. degrees
    'assume length units of (spherical) Earth radii
    x3 = Cos((90 - lat) * Pi / 180#)
    x1 = Cos(lat * Pi / 180#) * Cos(lon * Pi / 180#)
    x2 = Cos(lat * Pi / 180#) * Sin(lon * Pi / 180#)
    latlon2xyz = Array(x1, x2, x3)
End Function
Function innerangle(v1, v2)
    innerangle = Acos(v1(1) * v2(1) + v1(2) * v2(2) + v1(3) * v2(3))
End Function
Function dist(theta)
    dist = 6371# * theta  'using mean radius in km
End Function

_________________
Bob Rashkin

 

[Bong]

I forgot to unitize the xyz vector:

Function latlon2xyz(lat, lon)
    'lat,lon in dec. degrees
    'assume length units of (spherical) Earth radii
    x3 = Cos((90 - lat) * Pi / 180#)
    x1 = Cos(lat * Pi / 180#) * Cos(lon * Pi / 180#)
    x2 = Cos(lat * Pi / 180#) * Sin(lon * Pi / 180#)
    [red]mag=sqrt(x1*x1+x2*x2+x3*x3)
    latlon2xyz = Array(x1/mag, x2/mag, x3/mag)[/red]
End Function

_________________
Bob Rashkin