Image Sampler and Pick and Choose Problems.

Hey Guys, I'm trying to use an image sampler to generate data from which a Pick and Choose component will provide me with the data that I require. But i'm having a bit of trouble with this. 

What I am trying to do is generate the depth of my patterning through this method. I have 4 sets of polygons set on surfaces and I am trying to use the image sampler to provide me with a variation between these set depths. My intention is to then loft between these isolated curves and a set of base curves or to in order to create the required geometry. 

Does anyone know where I am going wrong with this? Both the GH and base Rhino Geometry are attached. 

Any help at all would be greatly appreciated!!