Update DisplayValueExtractor.cs (#509)

Converters/Civil3d/Speckle.Converters.Civil3dShared/Helpers/DisplayValueExtractor.cs

@@ -36,6 +36,11 @@ public IEnumerable<Base> GetDisplayValue(CDB.Entity entity)
   {
     switch (entity)
     {
+      // POC: we are sending featurelines as approximated polylines because they are 2.5d curves:
+      // they can have line or arc segments, and each vertex can have different elevations.
+      // there is no native type that can capture the full 3d representation of these curves.
+      // if this becomes essential, can explore a hack where each point is converted to 2d, and separate line/arc segments are calculated, and then their points readjusted with 3d z values
+      // SurveyFigures inherit from featureline
       case CDB.FeatureLine featureline:
         SOG.Polyline featurelinePolyline = _pointCollectionConverter.Convert(
           featureline.GetPoints(Autodesk.Civil.FeatureLinePointType.PIPoint)