Clamping a Flow Map on a mesh

Hey there,

In my scene i have a flowing river. I used a shader which supports flow maps. But the issue is that, the flow map lies overall on the world space, not directly on my mesh. For example, when i move my mesh, flow map stands still. So i must search the right position for my mesh to fit on the flowmap. It is really inconvenient and it looks like not right... I made a screenshot maybe it gets clearer:

[img]http://i.imgur.com/LlHPHTn.jpg[/img]

On the top left is my mesh, and the plane is just for example to see how the flowmaps laying on the mesh.

I was thinking of writing a script which makes the flow map lay on my mesh with correct sizes and positions. But i have no idea how to begin.. I am not even sure if it's the right way to solve it.

I appreciate of your help and ideas.