[away3d] Accessing plane (or any object) vertices (BROOMSTICK)

[timovirtanen]

How can I access object vertices? What I want to do is manipulate
every vertices y position independently.

Here is how I did it before:
for(var i:int = 0 ; i < geometry.vertices.length ; i++) {
...
}

And here is what I've tried with broomstick:

var sg : SubGeometry = geometry.subGeometries[0];
for(var i : int = 0 ; i < sg.numVertices ; i++)
{
        sg.vertexData[i] = Math.cos(_shift + _period) * _amplitude;
}
sg.updateVertexData(sg.vertexData);

I quite confused because the vertexData vector doesn't contain
vertices, but infact numbers??????