public int getDepth() {
        // The depth field is not an accurate indicator of depth.
        // Whenever the current spatial is an iterable node, the depth
        // value is exactly 1 greater than it should be.
        return !path.isEmpty() && current == path.getLast().node ? depth-1 : depth;
    }
Gets the current depth of the iterator.
<p>
The depth is how far away from the main spatial the
current spatial is. So, the main spatial's depth is 0,
all its children's depths is 1, and all <em>their</em>
children's depths is 2, etc.

@return current depth, or distance from the main spatial.
jme3-core/src/main/java/com/jme3/scene/SceneGraphIterator.java