Copy parts of a existing curve

[nic]

EDIT - Method found

Looking for a method to copy parts of a curve onto a new layer and wonder if someone can help.

I have a very large spiral (Grouped as 67 curves of 1000 nodes each).
On top of the spiral and centered onto the spiral line along its length are about 1500 non overlapping ellipses (so the each ellipse is centered on a different point of the spiral). The spiral is tightly wound so that the spiral may pass through the area of an ellipse several times but only one of these revolutions will pass through the ellipses center. It's only the section of the curve that passes through the center that I want to copy.

The size and center point of each ellipses is known and the spirals path is accurate to within about 0.01 of a mm.

What I would like is that the parts of the spiral that pass through the center of the ellipses be copied to a new layer so that the each ellipse has one curve - a part of the spiral - passing through its center and extending to the ellipsis edges.

Any help on finding the right way to achieve this would be appreciated.

nic

EDIT: Managed to do this - bit cumbersome but done. Used the ellipses in a rectangle to create a mask with just the holes empty, used mask to remove all lines outside of the area of the ellipses. Broke the remaining lines into separate objects and then used original ellipses to find objects in each center.