public Feature lineMidpoint(String layer) {
    try {
      return geometry(layer, source.lineMidpoint());
    } catch (GeometryException e) {
      e.log(stats, "feature_line_midpoint", "Error getting midpoint for " + source);
      return empty(layer);
    }
  }
Starts building a new point map feature at the midpoint of this line, or the longest line segment if a
multilinestring.

@param layer the output vector tile layer this feature will be written to
@return a feature that can be configured further.
planetiler-core/src/main/java/com/onthegomap/planetiler/FeatureCollector.java