[OpenLayers-Users] Function to create a geographically correct circle

[Michael]

Regular Polygons are fine for many applications.  I needed range rings 
for ocean races, which did not correctly reflect the projection of the 
map.  Although it projected like a nice round circle, the correct shape 
should have been oval.

Did not find a geographic circle function in OL, so I adapted one from 
one found online.

I present it here should anyone want it, or have a better idea, or want 
to point out that this was in OL all along.

*function GeoCircle(latin, lonin, radius)// thanks to VE site for basic 
algo. Returns an OL Polygon of diameter in nautical miles
   {
     var locs = new Array();
     var lat1 = latin * Math.PI/180.0;
     var lon1 = lonin * Math.PI/180.0;
     var d = radius/3440.07;// change this value to the radius of the 
Earth in your units
     var x;
     for (x = 0; x <= 360; x+=6)  //gives 60 points.  More than enough 
for a smooth circle most likely
     {
         var tc = (x / 90)* Math.PI / 2;
         var lat = 
Math.asin(Math.sin(lat1)*Math.cos(d)+Math.cos(lat1)*Math.sin(d)*Math.cos(tc));
         lat = 180.0 * lat / Math.PI;
         var lon;
          if (Math.cos(lat1)==0)
         {
             lon=lonin; // endpoint a pole
         }
         else
         {
             lon = ((lon1 - Math.asin(Math.sin(tc) * 
Math.sin(d)/Math.cos(lat1)) + Math.PI) % (2 * Math.PI)) - Math.PI;
         }
         lon = 180.0 * lon / Math.PI;
         var loc = new pt(lon,lat);
         locs.push(loc);
     }
     var poly = new OpenLayers.Feature.Vector(new 
OpenLayers.Geometry.Polygon(new OpenLayers.Geometry.LinearRing(locs)));

     return poly;  //this can be added to a map
}
*
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