[postgis-tickets] [PostGIS] #2093: Add extra policy argument to control ST_Simplify behavior

[PostGIS]

#2093: Add extra policy argument to control ST_Simplify behavior
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 Reporter:  robe         |       Owner:  strk         
     Type:  enhancement  |      Status:  new          
 Priority:  medium       |   Milestone:  PostGIS 2.2.0
Component:  postgis      |     Version:  trunk        
 Keywords:               |  
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Comment(by strk):

 So, current policy is:

  - lines: never collapse (this was not included in the previous attempt at
 giving policies, but it is to always keep at least 2 points, the first and
 the furthest)
  - polygon shells: null
  - polygon holes: remove

 So the proposed set of policies increases by adding a "do not allow
 collapses" for lines.
 I guess the equivalent for polygons (do not allow collapses) might also be
 useful, for both shells and holes. Ideally it would be composed by the
 first/last point + the farther from them + the farther from the segment
 composed by the previous two (for DP).

 Also, I was thinking that "topological invalid" is really never useful to
 be intentional, that is since  you have to keep at least 2 points for
 lines and 4 points for rings, they may as well be not topologically
 invalid (and a minimum number of points in output is likely to give you a
 valid return).

 So the possible policies become:

  - collapsed line: null, single vertex line, 2 vertices line [1], a point
  - collapsed shell: null [1], single vertex ring, 4 vertices ring, a line
 or point
  - collapsed hole: removed [1], single vertex ring, 4 vertices ring

 [1] current behavior

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/2093#comment:18>
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