code: public SimpleFeature convertDwgCircle( String typeName, String layerName, DwgCircle circle,
              int id ) {
          double[] center = circle.getCenter();
          double radius = circle.getRadius();
          Point2D[] ptos = GisModelCurveCalculator.calculateGisModelCircle(new Point2D.Double(
                  center[0], center[1]), radius);
          CoordinateList coordList = new CoordinateList();
          for( int j = 0; j < ptos.length; j++ ) {
              Coordinate coord = new Coordinate(ptos[j].getX(), ptos[j].getY(), 0.0);
              coordList.add(coord);
          }
          // close to create a polygon
          if ((ptos[ptos.length - 1].getX() != ptos[0].getX())
                  || (ptos[ptos.length - 1].getY() != ptos[0].getY())) {
              Coordinate coord = new Coordinate(ptos[0].getX(), ptos[0].getY(), 0.0);
              coordList.add(coord);
          }
  
          SimpleFeatureTypeBuilder b = new SimpleFeatureTypeBuilder();
          b.setName(typeName);
          b.setCRS(crs);
          b.add(THE_GEOM, Polygon.class);
          b.add(LAYER, String.class);
          SimpleFeatureType type = b.buildFeatureType();
          SimpleFeatureBuilder builder = new SimpleFeatureBuilder(type);
          LinearRing linearRing = gF.createLinearRing(coordList.toCoordinateArray());
          Geometry polygon = gF.createPolygon(linearRing, null);
          Object[] values = new Object[]{polygon, layerName};
          builder.addAll(values);
          return builder.buildFeature(typeName + "." + id);
      }
docs: Builds a polygon feature from a dwg circle.