How do you convert the radius decimals of a circle in Openlayers to Kilometers [duplicate]

Question

Possible Duplicate:
Unproject Radius with Openlayers with CRS:84 Projection

I allow a user to draw a circle in Openlayers.

I created an alert to show the radius of the circle.

I now need to convert the radius to kilometers.

For example 0.001788057579325097 (How many kilometers is this)

How do I change this to kilometers? I think its just the decimals that is the problem.

      // The Drag function is now made and called
         // Add Drag
     drag = new OpenLayers.Control.DragFeature(polygonLayer, {
     autoActivate: true,
     onComplete: displayRadius
     });


 function displayRadius(circle) {
     var area = circle.geometry.getArea();
     var radius = 0.565352 * Math.sqrt(area);
     alert(radius);
      }

Answer 1

You can create a path geometry from center to some point of your cercle and get the distance of the path (similar to what measure control does).