How to scale vtk border to image size?

I'm trying to plot three perpendicular planes of a volume using slice function and super impose a border on the resulting figure. Unfortunately the border is a vtk file and when I read it into a 3-dimensional array (Nx3), all dimensions span between 0 and 1. When I multiply dimensions to a number, I can see small size border along side of three planes but it is not the proper place to demonstrate. How can I put the border in vtk file in its place in my slice figure?