Hi Randy, Thanks for the code.
As I play with this data I am learning. The proximity approach evolved as I realized it would be nice to find al the citrus within a certain distance. Yea Google does this all the time but I need it to be non-web based. Thus the millions of database records. Interesting challenge that for sure. Appreciate, John… > On Apr 12, 2020, at 9:17 AM, Randy Kaempen <[email protected]> wrote: > > John, > >> On Apr 12, 2020, at 10:33 AM, John J Foster via 4D_Tech >> <[email protected] <mailto:[email protected]>> wrote: >> >> If you happen to find any 4D bearing/distance code (anything related to >> searching using longitude/latitude or both) I would enjoy looking at it. > > I had worked out these calculations with a mathematician called C. E. > Tiedemann many years ago. Here is an except from our emails, entitled > 'Ellipsoid Radius Calculation’. > > > Now I see what's going on. The figures in the table are merdianally > oriented radii of hypothetical spheres for which the surface curvature > matches the (a, b, e) ellipsoid at the specified latitude. Knowing these > allows use of fairly simple spherical formulae for computing distances > between points not too far apart on surfaces of ellipsoids. > > - - - - > > OK, I took a look at the URL and found my comment just below the material > we're looking at. In fact I remember having made those observations, but > it was a LONG time ago and at the momen I've no recollection of the context > in which they were made. > > But, all may not be lost: bouncing up a way in the text I found the > following: > > R' = a * (1 - e^2) / (1 - e^2 * (sin(lat))^2)^(3/2) > > The additional "^(3/2) will have the effect of increasing the denominator > and maybe bring things into agreement with your/our expectations. > > > This is the routine we came up with, which seems to work well. > > > // CalcDistance 11/24/02 > // > C_REAL($0;$1;$2;$3;$4;$Lat1;$Long1;$Lat2;$Long2;$DegToRad;$Work;$Distance) > // 11/24/02 > // > $Lat1:=$1 // 11/23/02 > $Long1:=$2 // 11/23/02 > $Lat2:=$3 // 11/23/02 > $Long2:=$4 // 11/23/02 > // > $DegToRad:=57.29577951308 // 11/23/02 > // > $Work:=(Sin($Lat1/$DegToRad)*Sin($Lat2/$DegToRad))+(Cos($Lat1/$DegToRad)*Cos($Lat2/$DegToRad))*Cos(($Long2/$DegToRad)-($Long1/$DegToRad)) > // 11/23/02 > $Distance:=3958.75*Arctan(Square root(1-($Work^2))/$Work) // 11/23/02 > // > $0:=$Distance // 11/23/02 > > > Feel free to use this if it’s of help to you. > > > Randy Kaempen > Intellex Corporation > ********************************************************************** 4D Internet Users Group (4D iNUG) Archive: http://lists.4d.com/archives.html Options: https://lists.4d.com/mailman/options/4d_tech Unsub: mailto:[email protected] **********************************************************************
