Clarify when lanes should share a reference line

Also fix a Doxygen error.

Signed-off-by: Thomas Bleher <thomas.tb.bleher@bmw.de>

osi_logicallane.proto

@@ -303,7 +303,11 @@ message LogicalLaneBoundary
 // - The red area is the area where \c l1 overlaps \c l2. This is recorded in
 //   #overlapping_lane of \c l1.
 //
-// Note: all these relations are also defined outside of intersections.
+// As can be seen in the images, the two highlighted lanes are neighbours for
+// part of their length, but it makes no sense for them to have the same
+// reference line, since they diverge significantly.
+//
+// Note: all the relations shown above are also defined outside of intersections.
 //
 message LogicalLane
 {
@@ -398,8 +402,9 @@ message LogicalLane
     // not required that the reference line has the same direction as the
     // driving direction of the lane.
     //
-    // Neighbouring lanes are strongly encouraged to use the same
-    // reference_line, so that vehicles that are next to each other on
+    // Neighbouring lanes (i.e. lanes that are neighbours and whose directions
+    // do not diverge significantly) are strongly encouraged to reference the
+    // same ReferenceLine, so that vehicles that are next to each other on
     // neighbouring lanes have comparable S positions.
     //
     // The S coordinate of the reference line makes it easy to find e.g. which

osi_referenceline.proto

@@ -134,7 +134,7 @@ message ReferenceLine
     //   dotted line).  Following the rules above, the one with the smallest S
     //   value is chosen (the red dotted line).
     // - \c P3 has a unique "nearest point" on the polyline. However, multiple
-    //   points map to the same ST coordinate as that of \c P3, e.g. \C P4
+    //   points map to the same ST coordinate as that of \c P3, e.g. \c P4
     //   (drawn in grey).
     // - Finally, \c P5 shows how the reference line is extended infinitely for
     //   points that are "outside" the reference line.