Changing default origin of Image Sampler

Hello,

I'm just learning to use grasshopper (recently watched the webinar), and I'd like to know how to change the origin of a bitmap sampler that is reading points from a Square Grid component. I am able to change the plane of the Square Grid, however the Image sampler seems to stay at (0,0,0) World.

What I'm hoping to accomplish is a perforated skin on a building using a black and white bit map to vary the perforations. Even when I set the C-plane to the face of my building and orient the Square Grid to it, the image seems to stay put (ie: and no longer influence the circle output)

What is the best way to accomplish this?

Thanks,

marc