Scenario

The regular buffer feature in FME 2011 or older produces a left or right side buffer, but only as a line feature.
This workspace (See Attachment: one-sided-buffer.fmwt) creates a left or right 'butt' style buffer as a polygon or area feature.

Note: In FME 2012 the Bufferer transformer has the option to create a left or right side polygon buffer.

Output

Above: The usual style of buffer; rounded and on both sides of the source feature.



Above: The style of buffer created by this workspace; butt-ended and on one side only of the source feature.

Method

A regular buffer is created and split in two. The unwanted part is discarded and the remaining parts pieced back together as a polygon feature.

Because the Intersector transformer is used to split the original buffer there would be problems if the existing line features or the intended buffers overlapped each other at all.

Happily, because all of the transformers used in this workspace have a group-by option this issue is avoided by applying a Counter transformer to the data and grouping by the count attribute.



Above: The workspace. Note the use of the Counter to create an ID which is used in the Intersector, CommonSegmentFinder and PolygonBuilder transformers.