# Rebuilding with constrains

Hi everybody,

Is it possible to rebuild a curve forcing it to pass by a concrete point?
Or to rebuild a surface forcing it to pass (as much as possible) by a constrain curve?

My workarounds to solve this is, in the curve case, to build two curves that merge in the point in question and then make them match, but there are two curves there, not one.

In the surface case I use to combine simplified surfaces with a Patch made of lines and an starting surface but the patch I’m getting at the end is a trimmed surface (not matchable) and isocurve directions, density and precision are not the most desirable at all.

Suggestions?

Thank you so much!

why do you have to rebuild the curves and the surface? there may be different approaches to fulfill your request. my first guess would be to use FitCrv or FitSrf but you dont have the amount of points under control.

you can also use flow to get a surface along an exact curve, but its really quite open at that point, so a bit more info what your intentions are would be helpful.

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Hi Jordi - I was going to suggest a two-stage operation with rebuild, then Patch to the curve using the rebuilt surface is its own starting surface - that seems to be what you’re doing, maybe? Can you post an example?
For the curves, you can Match your two curves for curvature with the Merge option - that’s how I do it, anyway…

-Pascal

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Hi Pascal and RichardZ,

With surfaces, I think I’m currently doing the operation that pascal suggests and it’s a useful way since I can control the degree and isocurve density of the patch through the starting surface, but at the end I’m always getting a trimmed surface (the patch) that is not working with match. That would be the full functionality in this case.
**Example:**The maroon surface is now coincident with the dashed line and I want it to be with the continuous one. Now I’m achieving it with a trimmed (by extending adjacents) surface. Could it be possible with a four sided and untrimmed surface? Maybe by dividing this face in two or three quad simplified faces?

With curves I would like to find the way to achieve it with a single curve at the end, maybe by joining this two curves and rebuilding, but that would break the ends continuity and bringing more mess than order I guess. Anyway it could be the best option if we combine `_MatchCrv` (at the ends, after rebuild) and `_Patience` to bring the middle points closer to the ideal trajectory manually.
Example: A transition single curve is needed to pass exactly by the red point with the minium amount of CPoints and curvature continuity at both ends.

Thank you very much