public ObjectNode toJson() {
        final ObjectNode node = JsonUtils.createObjectNode();
        JsonUtils.set(node, "bottomLeft", bottomLeft.toJson());
        JsonUtils.set(node, "topRight", topRight.toJson());
        return node;
    }
Creates a Viewport with given center which covers the area around it with given radius
main/src/main/java/cgeo/geocaching/location/Viewport.java