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Curve thru points tweak

DavidSurridge
1-Newbie

Curve thru points tweak

I've created a curve thru points (end point of another curve and end point of surface edge). The curve has been set to tangent/curvature continuous on both ends. I'd like to tweak this further but am unable to relocate any of the polygon points...they just won't move. I've done this many times before. Anyone have any ideas why they can't be adjusted?
4 REPLIES 4

David, You need to add more points on the curve. To do it go to the tweak window in the curve & use the other icon (spline with points on the curve). Then add points at the location you want to move. Then again switch back to the control polygon tab & move the points as desired. The reason for this is if you have curvature continuous curve it needs to constrain more points for maintaining the curvature continuity. The spline is basically a polynomial function based on the no. of points in the curve. More the no. of points , more you can move around. But the downside is the inflections (undulation) between the points will increase. So its a tricky thing.. Hope this helps, Rameet

Thanks Rameet. This has helped. It still doesn't make sense to me that I need to add the point, as I've used curve thru points in the past with curvature continuity and have always been able to tweak it by adjusting the polygon. Can't think of any reason why it's different this time. Thanks for the help. David

David, Some additional info that I think would be useful for you.. 1) For a straight curve between two points,just 2 points are required. 2) For maintaining tangency with a curve, an additional control point is required.This is to maintain the tangency between the other points and the end point.So if you have tangency curve between 2 curves, in reality you have 4 control points(minimum) that make the curve.You may have more but 4 is the least required to maintain tangency. 3) For curvature continuity another point is required on top of the tangency requirements. Pro/E uses 4 control points even for a point to point curve. When you add tangency the two additional points other than the end points move to a position that maintains tangency.You can move the tangency control points around. Now if you add curvature constraint on it , another control point is added to maintain curvature.But you can't move these.For maintaining curvature continuity with 6 control points , there is a unique solution only that's the reason you can't move any of the points. In case you go back to tangency contraint ,there are multiple solutions avialble ,so you can move the control points. If you need info on the mathematics you can provide your email ID & I can send that across. Rameet

I realize I am replying to a very old/dead thread, but, here goes anyways:

Rameet, I don't think I agree with your comment about there being only one unique solution isn't true.  For some reason Pro/E / Creo simply locks up the control of the curve if you have curvature continuity at both ends (and don't add additional points).  As proof that there are multiple solutions, you can set the end conditions back to tangency, move the points around, and when you set it back to curvature continuous, you get a different result.  I found a similar thread here: http://www.eng-tips.com/viewthread.cfm?qid=210041‌. 

PTC, if you are listening, it sure would be nice to be able to drag those control handles around while it is constrained to be curvature continuous...

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