Hi Franklin,
I guess you are using decimal degree as the unit of the map, right? If that is the case, then the number 0.0166 you got is in lon/lat unit too. Its actual length could be up to 1.85 kilometers (if it’s on the equator).
Here is some code that may help you to calculate the transverse radius:
RectangleShape boundingBoxOfCircle = circle.GetBoundingBox();
double y = (boundingBoxOfCircle.UpperLeftPoint.Y + boundingBoxOfCircle.LowerLeftPoint.Y) / 2;
double minX = boundingBoxOfCircle.LowerLeftPoint.X;
double maxX = boundingBoxOfCircle.LowerRightPoint.X;
PointShape point1 = new PointShape(minX, y);
PointShape point2 = new PointShape(maxX, y);
double length = DecimalDegreesHelper.GetDistanceFromDecimalDegrees(point1, point2, DistanceUnit.Kilometer);
double radius = length / 2;
Regards,
Tsui