---
title: Model tree structures
---

<p>
    A model is a tree structure which may contain paths, and it may also contain other models in a heirachy.
    Let's look at an example:
</p>

{% highlight javascript %}
//mounting plate

var makerjs = require('makerjs');

var plate = {
    models: {
        outer: makerjs.model.center(new makerjs.models.RoundRectangle(120, 100, 10)),
        bolts: makerjs.model.center(new makerjs.models.BoltRectangle(100, 80, 5))
    },
    paths: {
        hole: new makerjs.paths.Circle(25)
    }
};

var svg = makerjs.exporter.toSVG(plate);

document.write(svg);
{% endhighlight %}

<script>
    LiveDoc.evalLastCode();
</script>

<p>
    If we represent this drawing as a conceptual tree structure, it would look like this:
</p>

<pre>
plate
+-models
| +-outer
| | +-paths
| |   +-TopLeft
| |   +-Top
| |   +-TopRight
| |   +-Left
| |   +-Right
| |   +-BottomLeft
| |   +-Bottom
| |   +-BottomRight
| +-bolts
|   +-paths
|     +-TopLeft_bolt
|     +-TopRight_bolt
|     +-BottomLeft_bolt
|     +-BottomRight_bolt
+paths
 +-hole
</pre>

<p>
    (You may notice that this structure is reminiscent of a folder system on your computer.)
    We can easily traverse the tree when starting at the root. For example, let's change the radius of the BottomRight_bolt hole:
</p>

{% highlight javascript %}
//mounting plate

var makerjs = require('makerjs');

var plate = {
    models: {
        outer: makerjs.model.center(new makerjs.models.RoundRectangle(120, 100, 10)),
        bolts: makerjs.model.center(new makerjs.models.BoltRectangle(100, 80, 5))
    },
    paths: {
        hole: new makerjs.paths.Circle(25)
    }
};

//change radius of BottomRight bolt hole
plate.models.bolts.paths.BottomRight_bolt.radius = 2;

var svg = makerjs.exporter.toSVG(plate);

document.write(svg);
{% endhighlight %}

<script>
    LiveDoc.evalLastCode();
</script>

<p>
  We can access the BottomRight_bolt circle from the <code>plate</code> object downward. Notice that in this tree structure, you cannot access upwardly. 
  The <code>plate</code> object contains the <code>bolt</code> model which contains the <code>BottomRight_bolt</code> path, but <code>BottomRight_bolt</code>
  does not have a reference to its container. There are no properties of the <code>bottomRight_bolt</code> circle object which access anything up the tree. 
  It also does not have any references to its sibling circles within <code>bolt.paths</code>.
</p>

<p>
     Downward-only access is the nature of a simple object tree structure. We can overcome this using <b>routes</b>.
</p>