[Boost-commit] svn:boost r70726 - branches/release/boost/polygon/detail

Subject: [Boost-commit] svn:boost r70726 - branches/release/boost/polygon/detail
From: lucanus.j.simonson_at_[hidden]
Date: 2011-03-29 19:53:04

Author: ljsimons
Date: 2011-03-29 19:53:03 EDT (Tue, 29 Mar 2011)
New Revision: 70726
URL: http://svn.boost.org/trac/boost/changeset/70726

Log:
added simplify algorithm
Added:
   branches/release/boost/polygon/detail/polygon_simplify.hpp   (contents, props changed)

Added: branches/release/boost/polygon/detail/polygon_simplify.hpp
==============================================================================
--- (empty file)
+++ branches/release/boost/polygon/detail/polygon_simplify.hpp	2011-03-29 19:53:03 EDT (Tue, 29 Mar 2011)
@@ -0,0 +1,116 @@
+// Copyright 2011, Andrew Ross
+//
+// Use, modification and distribution are subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt).
+#ifndef BOOST_POLYGON_DETAIL_SIMPLIFY_HPP
+#define BOOST_POLYGON_DETAIL_SIMPLIFY_HPP
+#include <vector>
+
+namespace boost { namespace polygon { namespace detail { namespace simplify_detail {
+  
+  // Does a simplification/optimization pass on the polygon.  If a given
+  // vertex lies within "len" of the line segment joining its neighbor
+  // vertices, it is removed.
+  template <typename T> //T is a model of point concept
+  std::size_t simplify(std::vector<T>& dst, const std::vector<T>& src, 
+                       typename coordinate_traits<
+                       typename point_traits<T>::coordinate_type
+                       >::coordinate_distance len)
+  {
+    using namespace boost::polygon;
+    typedef typename point_traits<T>::coordinate_type coordinate_type;
+    typedef typename coordinate_traits<coordinate_type>::area_type ftype; 
+    typedef typename std::vector<T>::const_iterator iter;
+
+    std::vector<T> out;
+    out.reserve(src.size());
+    dst = src;
+    std::size_t final_result = 0;
+    std::size_t orig_size = src.size();
+
+    //I can't use == if T doesn't provide it, so use generic point concept compare
+    bool closed = equivalence(src.front(), src.back());
+
+    //we need to keep smoothing until we don't find points to remove
+    //because removing points in the first iteration through the 
+    //polygon may leave it in a state where more removal is possible
+    bool not_done = true;
+    while(not_done) {
+      if(dst.size() < 3) {
+        dst.clear();
+        return orig_size;
+      }
+      
+      // Start with the second, test for the last point
+      // explicitly, and exit after looping back around to the first.
+      ftype len2 = ftype(len) * ftype(len);
+      for(iter prev=dst.begin(), i=prev+1, next; /**/; i = next) {
+        next = i+1;
+        if(next == dst.end())
+          next = dst.begin();
+        
+        // points A, B, C
+        ftype ax = x(*prev), ay = y(*prev);
+        ftype bx = x(*i), by = y(*i);
+        ftype cx = x(*next), cy = y(*next);
+        
+        // vectors AB, BC and AC:
+        ftype abx = bx-ax, aby = by-ay;
+        ftype bcx = cx-bx, bcy = cy-by;
+        ftype acx = cx-ax, acy = cy-ay;
+        
+        // dot products
+        ftype ab_ab = abx*abx + aby*aby;
+        ftype bc_bc = bcx*bcx + bcy*bcy;
+        ftype ac_ac = acx*acx + acy*acy;
+        ftype ab_ac = abx*acx + aby*acy;
+        
+        // projection of AB along AC
+        ftype projf = ab_ac / ac_ac;
+        ftype projx = acx * projf, projy = acy * projf;
+        
+        // perpendicular vector from the line AC to point B (i.e. AB - proj)
+        ftype perpx = abx - projx, perpy = aby - projy;
+        
+        // Squared fractional distance of projection. FIXME: can
+        // remove this division, the decisions below can be made with
+        // just the sign of the quotient and a check to see if
+        // abs(numerator) is greater than abs(divisor).
+        ftype f2 = (projx*acx + projy*acx) / ac_ac;
+        
+        // Square of the relevant distance from point B:
+        ftype dist2;
+        if     (f2 < 0) dist2 = ab_ab;
+        else if(f2 > 1) dist2 = bc_bc;
+        else            dist2 = perpx*perpx + perpy*perpy;
+        
+        if(dist2 > len2) {
+          prev = i; // bump prev, we didn't remove the segment
+          out.push_back(*i);
+        }
+        
+        if(i == dst.begin())
+          break;
+      }
+      std::size_t result = dst.size() - out.size();
+      if(result == 0) {
+        not_done = false;
+      } else {
+        final_result += result;
+        dst = out;
+        out.clear();
+      }
+    } //end of while loop
+    if(closed) {
+      //if the input was closed we want the output to be closed
+      --final_result;
+      dst.push_back(dst.front());
+    }
+    return final_result;
+  }
+
+
+}}}}
+
+#endif