Calculating straight line distances 1

[bdenson]

Given the Latitude and Longtitude of two points, and the radius of the Earth in miles, I need to work out the distance between the two points.

I have been given the calulations

Lat1=52.47758N Lon1=1.90983W
Lat2=50.80029N Lon2=1.08825W
Delta of Lat (Dlat)=Lat2-Lat1
Delta of Lon (Dlon)=Lon2-lon1
a={sin(Dlat/2)}^2 + [cos(lat1) * cos(lat2) * {sin(dlon/2)}^2]

c=2*arcsin(min1,sqrt(a))
d=Radius*c

d being the distance between the two points. I have tried to write this forumla in Foxpro, but I'm getting 5430 miles instead of around 124 miles.

Can anyone help?

Barry Yesterday is history
Tomorrow is a mystery
and todays a gift... ...thats why we call it the present.

 

[Neil Toulouse]

The trig functions in VFP are expressed in radians. Could this be the problem? "I like work. It fascinates me. I can sit and look at it for hours..."

 

[jmcd0719]

Here are links with formulas for calculating distances.

http://www.meridianworlddata.com/Distance-Calculation.asp

http://www.darkshire.org/~jhkim/programming/zipcodes/math.html

http://isaac.williamsport.wa.k12.md.us/~ctrout/sciproj/MATLAB/#latlon

http://www.chilidog.com/zip/zipnotes.html

 

[Neil Toulouse]

Another useful document (for UK Ordnance Survey based co-ordinates)is "A guide to co-ordinate systems in Great Britain" which can be obtained from:

http://www.gps.gov.uk

This has the formulae for converting from longitude/latitude to eastings/northings (and vice-versa) and also for converting OS grid references (eg SN123456) to eastings/northings, based on different projections and ellipsoids.

Neil "I like work. It fascinates me. I can sit and look at it for hours..."

 

[Mike Lewis]

Barry,

I vaguely recall an article in Foxtalk - maybe two or three years ago - which gave some VFP code for the calculation you want. Sorry, I don't have the reference to hand, but you could try searching the Foxtalk index at

http://www.pinpub.com

Mike
Mike Lewis
Edinburgh, Scotland

http://www.ml-consult.demon.co.uk

 

[GriffMG]

Barry,

What is Min1?

Why would ArcSin need two parameters?

Regards

Griff
Keep [Smile]ing

 

[GriffMG]

Is this the right formula?

CLEAR
Lat1=52.47758
Lon1=1.90983
Lat2=50.80029
Lon2=1.08825
Dlat=Lat2-Lat1
Dlon=Lon2-lon1
a=(sin(dtor(Dlat/2)))^2 + (cos(dtor(lat1)) * cos(dtor(lat2)) * (sin(dtor(dlon/2)))^2)

Radius = 4214.618316927 
c=2*asin(sqrt(a))
d=Radius*c

? d

It yields about 128

Regards

Griff
Keep [Smile]ing

 

[GriffMG]

PS,

If you assume just 4000 miles for the radius, you get an answer closer to the one you mentioned!

HTH Regards

Griff
Keep [Smile]ing

 

[bdenson]

Thanks Guys!!!

Problem solved now.

Got a solution from FoxTalk - Thanks Mike

FYI - Griff, You solution works too.

Thanks Again

Barry Yesterday is history
Tomorrow is a mystery
and todays a gift... ...thats why we call it the present.

 

[BillGravell]

Could you send me the text of the FoxTalk article you found. I tried to look at it, but could get into it. Thanks,

Bill

 

[Mike Gagnon]

BillGravell

The arctical is called "Calculate the distance between two points" (July 1998). Do a search in FoxTalk's past issues for "Distance" (w/o quotes) you should find it. Although it is for members, the online membership if free. Mike Gagnon

If you want to get the best response to a question, please check out FAQ184-2483 first.