the perimeter of a shape combined of several shapes
<p>I have several svg paths, and I'd like to get the outmost path of the combined shape. For instance for the following paths:</p>

<pre><code>&lt;path d="M 90 10 L 50 50 L 50 10 z"/&gt;
&lt;path d="M 130 50 L 130 90 L 90 90 z"/&gt;
&lt;path d="M 50 50 L 90 10 L 90 50 L 70 70 z"/&gt;
&lt;path d="M 10 90 L 10 50 L 50 50 L 70 70 L 50 90 z"/&gt;
&lt;path d="M 70 110 L 70 130 L 50 130 L 50 90 z"/&gt;
&lt;path d="M 90 50 L 130 50 L 70 110 L 50 90 z"/&gt;
&lt;path d="M 90 90 L 90 130 L 70 130 L 70 110 z"/&gt;
</code></pre>

<p>I'd like to get</p>

<pre><code>&lt;path d="M 50 10 L 90 10 L 90 50 L 130 50 L 130 90 L 90 90 L 90 130 L 50 130 L 50 90 L 10 90 L 10 50 L 50 50 z"/&gt;
</code></pre>

<p>What would be a good algorithm to get to this path?</p>