Is the attached project any use?
I've created a Circle object library from the code here:
Circle.java
It has these methods:
Initialize (Center As Location, Radius As Double)
Initialize the Circle object.
Center is a Location object - you must include the GPS library in your project.
Radius is a distance in meter units.
Area As Double
Returns the area of the circle in units of square meters.
Contains (aLocation as Location) As Boolean
Returns whether this circle object contains aLocation.
Intersects (aCircle As Circle) As Boolean
Return whether this circle object intersects aCircle.
Perimeter As Double
Returns the length of this circle object's perimeter.
A Circle object is not an Activity object - you can declare it in Process_Globals, Globals or locally in a Sub.
Give it a test and if it does what you require but need additional methods post again.
Martin.