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<div class='docs'><h1>visvalingam.py</h1></div>
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<a class='octothorpe' href='#section-0'>#</a>
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<div class='code'>
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<div class="highlight"><pre></pre></div>
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<a class='octothorpe' href='#section-1'>#</a>
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<p>Visvalingam-Whyatt simplification</p>
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<div class='code'>
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<div class="highlight"><pre><span class="k">def</span> <span class="nf">simplify_visvalingam_whyatt</span><span class="p">(</span><span class="n">points</span><span class="p">,</span> <span class="n">tolerance</span><span class="p">):</span></pre></div>
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<div class='section' id='section-2'>
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<a class='octothorpe' href='#section-2'>#</a>
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<p>mplementation borrowed from @migurski:
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ttps://github.com/migurski/Bloch/blob/master/Bloch/<strong>init</strong>.py#L133</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">points</span><span class="p">)</span> <span class="o"><</span> <span class="mi">3</span><span class="p">:</span>
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<span class="k">return</span>
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<span class="k">if</span> <span class="n">points</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">simplified</span><span class="p">:</span>
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<span class="k">return</span>
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<span class="n">min_area</span> <span class="o">=</span> <span class="n">tolerance</span> <span class="o">**</span> <span class="mi">2</span>
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<span class="n">pts</span> <span class="o">=</span> <span class="nb">range</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">points</span><span class="p">))</span> <span class="c"># pts stores an index of all non-deleted points</span>
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<span class="k">while</span> <span class="nb">len</span><span class="p">(</span><span class="n">pts</span><span class="p">)</span> <span class="o">></span> <span class="mi">4</span><span class="p">:</span>
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<span class="n">preserved</span><span class="p">,</span> <span class="n">popped</span> <span class="o">=</span> <span class="nb">set</span><span class="p">(),</span> <span class="p">[]</span>
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<span class="n">areas</span> <span class="o">=</span> <span class="p">[]</span>
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<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">pts</span><span class="p">)</span> <span class="o">-</span> <span class="mi">1</span><span class="p">):</span>
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<span class="n">x1</span><span class="p">,</span> <span class="n">y1</span> <span class="o">=</span> <span class="n">points</span><span class="p">[</span><span class="n">pts</span><span class="p">[</span><span class="n">i</span> <span class="o">-</span> <span class="mi">1</span><span class="p">]]</span>
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<span class="n">x2</span><span class="p">,</span> <span class="n">y2</span> <span class="o">=</span> <span class="n">points</span><span class="p">[</span><span class="n">pts</span><span class="p">[</span><span class="n">i</span><span class="p">]]</span>
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<span class="n">x3</span><span class="p">,</span> <span class="n">y3</span> <span class="o">=</span> <span class="n">points</span><span class="p">[</span><span class="n">pts</span><span class="p">[</span><span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">]]</span></pre></div>
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<div class='section' id='section-3'>
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<a class='octothorpe' href='#section-3'>#</a>
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<p>compute and store triangle area</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="n">areas</span><span class="o">.</span><span class="n">append</span><span class="p">((</span><span class="n">_tri_area</span><span class="p">(</span><span class="n">x1</span><span class="p">,</span> <span class="n">y1</span><span class="p">,</span> <span class="n">x2</span><span class="p">,</span> <span class="n">y2</span><span class="p">,</span> <span class="n">x3</span><span class="p">,</span> <span class="n">y3</span><span class="p">),</span> <span class="n">i</span><span class="p">))</span>
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<span class="n">areas</span> <span class="o">=</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">areas</span><span class="p">)</span>
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<span class="k">if</span> <span class="ow">not</span> <span class="n">areas</span> <span class="ow">or</span> <span class="n">areas</span><span class="p">[</span><span class="mi">0</span><span class="p">][</span><span class="mi">0</span><span class="p">]</span> <span class="o">></span> <span class="n">min_area</span><span class="p">:</span></pre></div>
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<a class='octothorpe' href='#section-4'>#</a>
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<p>there's nothing to be done</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="k">for</span> <span class="n">pt</span> <span class="ow">in</span> <span class="n">points</span><span class="p">:</span>
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<span class="n">pt</span><span class="o">.</span><span class="n">simplified</span> <span class="o">=</span> <span class="bp">True</span>
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<span class="k">break</span></pre></div>
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<a class='octothorpe' href='#section-5'>#</a>
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<p>Reduce any segments that makes a triangle whose area is below
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the minimum threshold, starting with the smallest and working up.
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Mark segments to be preserved until the next iteration.</p>
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</div>
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<div class='code'>
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<div class="highlight"><pre> <span class="k">for</span> <span class="p">(</span><span class="n">area</span><span class="p">,</span> <span class="n">i</span><span class="p">)</span> <span class="ow">in</span> <span class="n">areas</span><span class="p">:</span>
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<span class="k">if</span> <span class="n">area</span> <span class="o">></span> <span class="n">min_area</span><span class="p">:</span></pre></div>
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<a class='octothorpe' href='#section-6'>#</a>
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<p>there won't be any more points to remove.</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="k">break</span>
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<span class="k">if</span> <span class="n">i</span> <span class="o">-</span> <span class="mi">1</span> <span class="ow">in</span> <span class="n">preserved</span> <span class="ow">or</span> <span class="n">i</span> <span class="o">+</span> <span class="mi">1</span> <span class="ow">in</span> <span class="n">preserved</span><span class="p">:</span></pre></div>
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<a class='octothorpe' href='#section-7'>#</a>
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<p>the current segment is too close to a previously-preserved one.
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print "-pre", preserved</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="k">continue</span>
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<span class="n">points</span><span class="p">[</span><span class="n">pts</span><span class="p">[</span><span class="n">i</span><span class="p">]]</span><span class="o">.</span><span class="n">deleted</span> <span class="o">=</span> <span class="bp">True</span>
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<span class="n">popped</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">i</span><span class="p">)</span></pre></div>
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<div class='section' id='section-8'>
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<a class='octothorpe' href='#section-8'>#</a>
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<p>make sure that the adjacent points</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="n">preserved</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">i</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span>
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<span class="n">preserved</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">)</span>
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<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">popped</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span></pre></div>
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<div class='section' id='section-9'>
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<a class='octothorpe' href='#section-9'>#</a>
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<p>no points removed, so break out of loop</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="k">break</span>
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<span class="n">popped</span> <span class="o">=</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">popped</span><span class="p">,</span> <span class="n">reverse</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
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<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="n">popped</span><span class="p">:</span></pre></div>
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<a class='octothorpe' href='#section-10'>#</a>
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<p>remove point from index list</p>
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<div class='code'>
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<div class="highlight"><pre> <span class="n">pts</span> <span class="o">=</span> <span class="n">pts</span><span class="p">[:</span><span class="n">i</span><span class="p">]</span> <span class="o">+</span> <span class="n">pts</span><span class="p">[</span><span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">:]</span>
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<span class="k">for</span> <span class="n">pt</span> <span class="ow">in</span> <span class="n">points</span><span class="p">:</span>
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<span class="n">pt</span><span class="o">.</span><span class="n">simplified</span> <span class="o">=</span> <span class="bp">True</span></pre></div>
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<div class='section' id='section-11'>
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<a class='octothorpe' href='#section-11'>#</a>
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<p>computes the area of a triangle given by three points
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implementation taken from:
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http://www.btinternet.com/~se16/hgb/triangle.htm</p>
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</div>
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<div class='code'>
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<div class="highlight"><pre><span class="k">def</span> <span class="nf">_tri_area</span><span class="p">(</span><span class="n">x1</span><span class="p">,</span> <span class="n">y1</span><span class="p">,</span> <span class="n">x2</span><span class="p">,</span> <span class="n">y2</span><span class="p">,</span> <span class="n">x3</span><span class="p">,</span> <span class="n">y3</span><span class="p">):</span></pre></div>
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<a class='octothorpe' href='#section-12'>#</a>
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<div class="highlight"><pre> <span class="k">return</span> <span class="nb">abs</span><span class="p">((</span><span class="n">x2</span><span class="o">*</span><span class="n">y1</span><span class="o">-</span><span class="n">x1</span><span class="o">*</span><span class="n">y2</span><span class="p">)</span><span class="o">+</span><span class="p">(</span><span class="n">x3</span><span class="o">*</span><span class="n">y2</span><span class="o">-</span><span class="n">x2</span><span class="o">*</span><span class="n">y3</span><span class="p">)</span><span class="o">+</span><span class="p">(</span><span class="n">x1</span><span class="o">*</span><span class="n">y3</span><span class="o">-</span><span class="n">x3</span><span class="o">*</span><span class="n">y1</span><span class="p">))</span><span class="o">/</span><span class="mf">2.0</span>
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</pre></div>
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