The attached is a work in progress, but try it out. Some of the things I would like to change have to do with contour lines at different elevations, since I have seen topographical drawings in which each contour line is actually at its designated elevation. The attached would not work on such a drawing, because the IntersectWith method requires the intersecting things to be at the same elevation. Some other things in the description at the top are also "wish list" items, and are not true yet, either. But for things in the same plane in the World Coordinate System, it seems to work, for both open-ended and closed contours. And it can use certain things other than Polylines, and has some other bells and whistles I took from another routine I wrote.
If it works for you, I will continue to refine it, though I'm now thinking about making something with much wider application [for example, something that would let the User choose *any* number of intermediate strokes, or choose to draw lines of any specified length, not just toward another selected object, or choose to draw them centered on the selected path rather than to one side, etc., etc.]. If I come up with something that does all the things I have in mind, it would do what you want with the right options, but would also do many other things.
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Kent Cooper
Kent Cooper, AIA