Syntax

   FACTORY_DEF <ReaderKeyword> SnappingFactory 
   [FACTORY_NAME <factory name>] 
   [INPUT [BASE|CANDIDATE] FEATURE_TYPE <feature type> 
      [<attribute name> <attribute value>]* 
      [<feature function>]*]* 
   SNAP_TYPE (END_NODE|VERTEX) 
   SNAP_TOLERANCE <distance> 
   [HANDLE_ARCS_ELLIPSES_AND_TEXT [(YES|NO)]]
   [EXTEND_LINES_TO_SNAP (ALWAYS|FORWARD_ONLY|NEVER)]
   [SAVE_SHORT_LINES [(YES|NO)]
   [GROUP_BY [<attribute name>]+]
   [OUTPUT (SNAPPED|UNTOUCHED) FEATURE_TYPE <feature type> 
      [<attribute name> <attribute value>]* 
      [<feature function>]*]*

Overview

      Note: This factory is not supported by FME Base Edition.
      
   This factory takes a series of features that match the input specification 
   and performs snapping on the features that lie within the specified tolerance 
   from other features that match the input specification. This factory can be 
   used to perform some cleaning operations on data during a translation. 

   The factory operates in two modes:

      The input BASE clause is not specified, resulting in a snapping "free-for-
      all" between the CANDIDATE features where the features are within the 
      SNAP_TOLERANCE value. 

      The BASE clause is specified, and therefore no snapping is performed 
      within the BASE features and within the CANDIDATE features. In this mode 
      only CANDIDATE features are snapped to BASE features.

   There are currently three types of snapping done by the factory, and this is 
   specified by the SNAP_TYPE directive.

   When the value for SNAP_TYPE is ALL_SNAP, then features are processed
   using the new snapping functionality within the Intersector. 
   EXTEND_LINES_TO_SNAP and SAVE_SHORT_LINES parameter are both ignored.


   When the value for SNAP_TYPE is END_NODE, then features are processed as 
   described below.

      The end nodes of linear features are considered as candidates for 
      snapping. All other vertices will remain unchanged. 

      Point features are also snapped if they are within the specified snapping 
      tolerance. 

      Polygon features are unchanged.

      The EXTEND_LINES_TO_SNAP clause may be specified, causing the factory to 
      add another point to the line to complete the snap rather than move the 
      existing vertex. If the clause is given the value ALWAYS, then a line is 
      always added to complete the snap. If the value is FORWARD_ONLY, then the 
      snapping is only done if the new point is closer to the existing endpoint 
      than the previous point, thereby assuring that the line does not have a 
      hard change in direction.

   When SNAP_TYPE is VERTEX:

      Vertex-to-vertex snapping will be performed for vertices that are within 
      <tolerance> of each other.

      Point features will be snapped together (or to a linear feature).

      Area features will be altered by this operation as its vertices are 
      snapped.

      The EXTEND_LINES_TO_SNAP clause is ignored.

   SNAP_TOLERANCE specifies the distance that the snapping occurs between 
   features. This distance is in ground units.

   If the GROUP_BY clause is given, then each feature will only be snapped to 
   other features that contain the same values as itself in the attributes 
   specified by this clause.

   Any feature that undergoes dimensional collapse as a result of being snapped 
   will be logged as "degenerate" and dropped. "Dimensional collapse" refers to 
   a line or area that becomes a point, or an area that becomes a line.

   If SAVE_SHORT_LINES is specified, any features entering the factory whose 
   length is less than or equal to the tolerance will be treated specially: they 
   will be output as UNTOUCHED, and other features (but not other short 
   features) will be able to snap to them. If the option is not selected, 
   features like this will collapse to a single point and will be dropped.

   If the FME_GEOMETRY_HANDLING directive is set to "yes" in the mapping file, 
   arcs are snapped as linear features, and ellipses are not snapped; otherwise, 
   arcs and ellipses are both snapped as point features located at their 
   respective center points.

Output Tags

   The SnappingFactory supports two output tags.
   
   SNAPPED  
   
      Features whose geometry is changed by the factory are output through this 
      tag.
   
   UNTOUCHED   
   
      Features that leave the factory without being changed are output through 
      this tag.

TO BE RESOLVED

   HANDLE_ARCS_ELLIPSES_AND_TEXT clause added to Syntax section above, but not 
   documented.