protected void assembleVertexControlPoints(DrawContext dc) {
    Terrain terrain = dc.getTerrain();
    ExtrudedPolygon polygon = this.getPolygon();

    Position refPos = polygon.getReferencePosition();
    Vec4 refPoint = terrain.getSurfacePoint(refPos.getLatitude(), refPos.getLongitude(), 0);

    int altitudeMode = polygon.getAltitudeMode();
    double height = polygon.getHeight();

    Vec4 vaa = null;
    double vaaLength = 0; // used to compute independent length of each cap vertex
    double vaLength = 0;

    int i = 0;
    for (LatLon location : polygon.getOuterBoundary()) {
      Vec4 vert;

      // Compute the top/cap point.
      if (altitudeMode == WorldWind.CONSTANT || !(location instanceof Position)) {
        if (vaa == null) {
          // Compute the vector lengths of the top and bottom points at the reference position.
          vaa = refPoint.multiply3(height / refPoint.getLength3());
          vaaLength = vaa.getLength3();
          vaLength = refPoint.getLength3();
        }

        // Compute the bottom point, which is on the terrain.
        vert = terrain.getSurfacePoint(location.getLatitude(), location.getLongitude(), 0);

        double delta = vaLength - vert.dot3(refPoint) / vaLength;
        vert = vert.add3(vaa.multiply3(1d + delta / vaaLength));
      } else if (altitudeMode == WorldWind.RELATIVE_TO_GROUND) {
        vert =
            terrain.getSurfacePoint(
                location.getLatitude(),
                location.getLongitude(),
                ((Position) location).getAltitude());
      } else // WorldWind.ABSOLUTE
      {
        vert =
            terrain
                .getGlobe()
                .computePointFromPosition(
                    location.getLatitude(),
                    location.getLongitude(),
                    ((Position) location).getAltitude() * terrain.getVerticalExaggeration());
      }

      Position vertexPosition = this.wwd.getModel().getGlobe().computePositionFromPoint(vert);

      this.controlPoints.add(
          new ControlPointMarker(
              MOVE_VERTEX_ACTION, vertexPosition, vert, this.vertexControlAttributes, i));
      i++;
    }
  }
  /**
   * Remove a vertex from the polygon.
   *
   * @param vertexToRemove the vertex to remove.
   */
  protected void removeVertex(ControlPointMarker vertexToRemove) {
    ExtrudedPolygon polygon = this.getPolygon();
    ArrayList<LatLon> locations = new ArrayList<LatLon>(this.controlPoints.size() - 1);

    for (LatLon latLon : polygon.getOuterBoundary()) {
      locations.add(latLon);
    }
    locations.remove(vertexToRemove.getIndex());

    polygon.setOuterBoundary(locations);
  }