createOrUpdatePointerFeature_(vertex) {
    let vertexFeature = this.vertexFeature_;
    if (!vertexFeature) {
      vertexFeature = new Feature(new Point(vertex));
      this.vertexFeature_ = vertexFeature;
      this.vertexOverlay_.getSource().addFeature(vertexFeature);
    } else {
      const geometry = vertexFeature.getGeometry();
      geometry.setCoordinates(vertex);
    }
    return vertexFeature;
  }
@param {import("../coordinate.js").Coordinate} vertex location of feature
@return {Feature} vertex as feature
@private