Changes between Initial Version and Version 1 of UsersWikiExamplesSpikeAnalyzer

Timestamp:

12/03/09 06:15:38 (15 years ago)

Author:

nik1166

Comment:

--

UsersWikiExamplesSpikeAnalyzer

@@ +1 @@
+= Spike-Analyzer =
+
+Function for determining spikes in polygons
+
+This function tries to determine spikes by using the buffer-function. A small negative buffer removes spikes and decreases the perimeter of the polygon significantly. It should be used either as a preselection for the spike-remover to increase performance or stand-alone for simple analyze purposes. Default values are (-0.02 [meters], 1) and lead to useful results.
+
+= Function =
+{{{
+
+-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+-- 
+-- $Id: spike_analyzer.sql 2009-12-01 08:00 Andreas Schmidt(andreas.schmidtATiz.bwl.de)  &  Nils Krüger(nils.kruegerATiz.bwl.de) $
+--
+-- spike_analyzer - helps to find spikes in polygons
+-- http://www.izlbw.de/
+-- Copyright 2009 Informatikzentrum Landesverwaltung Baden-Württemberg (IZLBW) Germany
+-- Version 1.0
+--
+-- This is free software; you can redistribute and/or modify it under
+-- the terms of the GNU General Public Licence. See the COPYING file.
+-- This software is without any warrenty and you use it at your own risk
+--  
+-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+
+create or replace function spike_analyzer(geom geometry, testbuffer float, spikeindex float)
+returns boolean as
+$$
+
+select case when st_geometrytype($1) in ('ST_Polygon', 'ST_MultiPolygon') then
+        (select case when 
+                (select max(index) from
+                        (select (case when (st_perimeter(geom) > 0 and st_area(geom) > 0 and st_perimeter(st_buffer(geom, $2)) > 0)
+                                then st_area(st_buffer(geom, $2)) / st_area(geom) / (st_perimeter(st_buffer(geom, $2))/st_perimeter(geom))
+                                else 0
+                        end) as index from
+                                (
+                                        select (st_dumprings($1)).geom
+                                ) as sub
+                        ) as max
+                ) > $3
+                then true 
+                else false 
+        end)
+        else false 
+end;
+
+$$
+language 'sql'
+immutable
+;
+
+comment on function public.tet_spike_analyzer(geometry, float, float) is 'Function to detect spikes in polygon-features, default values are (-0.02 [meters], 1) and lead to useful results';
+
+}}}