Spline sketching problem.

mor

When trying to constrain a spline somewhere along its middle (such as: pass through a point, or even worse – also tangent to, say, a horizontal line through that point) - I find myself fighting a disturbing dependency between the two spline's end curves guides.

How can I free that dependency?

Thank you

Avshalom.

Narayan_K

@ avshalom_mor, As my under standing you are not able to completely constrain a spline.Even if you constrain all points,spline can be modify by dragging the end tangent lines of spline on both side.If so then you have to constrain the end point of tangent line(point with white at the center).
Also you can constrain the spline by using "fix" constrain.

mor

My problem is not constraining a spline.
the problem is that before you constrain the ends guides, when you constrain the spline by attaching it to a point or line (say Tangent constraint) somewhere on the spline line - both ends guides "gain" some inter-depended relations between them that seriously limit your freedom of shaping the spline.
I will try to explain in other words: After I entered the point/line tangent constraint to the spline,  each time I try to move one guide - the other guide moves too; Also - the guide I'm trying to move happens to be (heavily) constrained in some way by some relations to that other guide.
Sorry I couldn't upload a simple sketch example here.    
 

Narayan_K

@ avshalom_mor, I have shown one example here,


In this video all spline points are constrained except guide point.after applying tangent constrain one guide line moves only in horizontal to the line/edge.It is to maintain the tangent between the line and that end point of spline.
But i didn't find any dependency between two guide curves(tangent lines of spline).
I apologize if i m explaining something different than you.

mor

Hi Narayan,
It seems to me that the case you show doesn't apply to my problem.
Please try the following:
1.draw: a rectangle. a point within it (somewhere near the center). a horizontal line attached to the point.  make them all fixed.
2. draw a spline from lower left corner to the upper right corner. now attach the spline to the point. try to make a few curved lines options from the spline.
3. make the spline tangent to the horizontal line. try again to make different curves from the spline.
If you do not encounter any problem - please let me see how you do that (like your example above).

Narayan_K

@ avshalom_mor ,Here is the illustration of your scenario,


Since the the spline is tangent to the line at the end point,guide point are not allowed to move in some region where the tangent will not be there.

In spline you have only two curves(only one point in spline other than end points). Both curves are trying to maintain tangent on one end with end point of horizontal line.so while moving one guide point it changes the shape of a curve and to maintain tangency the other curves also moves accordingly.You can reduce the dependency by adding more point on the curve.
To keep other point fixed you can add fix constrain to that point

mor

So the solution is to build two splines connected at the tangent point?
But look - In this case I can make both lines' ends tangent to the horizontal line point and still move freely at each end.
may be there should be some way to change OnShape spline's logic?
Using spline in the above cases is actually useless.