How to control specific points on the Sine Curve?

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Permalink Reply by Paul N Jeffries on September 3, 2017 at 8:44am

Are the curves in Rhino or in Grasshopper only?

In Rhino, you could use the PointsOn command to turn on control points (or EditPtsOn for edit points) and then simply move the end control points down to the level you want.

If you want to do this in Grasshopper it's a little more involved.  You'll need to use something like the following sequence of components:

- Control Points (to get the control points of the curve)

- List Item (to get the start or end control point)

- Deconstruct (to get the coordinates of that point)

- Construct Point (to rebuild the point with the X and Y coordinates of the original, but the new Z coordinate you want to specify)

- Replace Items (to replace the original start/end point in the control points list with the one you just created)

- NurbsCurve (to rebuild the curve with the modified set of control points, plus the weights and knots of the original)

If the points you want to move are not the curve ends (it's a little hard to tell from the images above) then it's even more difficult since Grasshopper doesn't really have an Edit Point equivalent - probably your best bet is to Divide the curve, move down the relevant points and then use Interpolate to rebuild a curve through that modified set of points.

Permalink Reply by Kay Kay on September 3, 2017 at 9:16am

Thank you very much Paul. Helps me a lot! I will have a try on this

Permalink Reply by Joseph Oster on September 3, 2017 at 8:52am

I looked at this too and noticed that the original curves are extremely "wiggly" with high frequency sine waves, but those curves are radically smoothed out using 'Rebuild'.  As Paul said, your best bet is to arrange your original input curves to touch the building where you want - and then you'll want to minimize the 'Rebuild' effect because it distorts the curves too much and they won't touch anymore.

Permalink Reply by Kay Kay on September 3, 2017 at 9:18am

Yeh Joseph.. I dont know why the original curves look so bad and it is very hard to control as well. is it coz of the formula that I used? let me try again. Thanks for your suggestion! 

Permalink Reply by Joseph Oster on September 3, 2017 at 9:55am

Looking again now...  had to "turn the lights on", enable preview on early curves, disable the slow part ('SrfSplit')...  Then tried decreasing the 'Count' value from 77 to 22 (changed maximum from 1000 to 100).  I by-passed 'Rebuild (ReB)' but found that 'SDivide' after 'Loft' failed because 'Loft' had produced a Brep instead of a surface.  So I used 'Loft Options' to 'Rebuild' and got a surface again.

I'll stop at this point and give you what I have.  I think if you experiment with the point count and/or play with the 'Loft option' rebuild count and 'Z' values for the 'IntCrvs', and perhaps rotate the resulting surface to align with your anchor points, you can make this work.  Enable 'SrfSplit' only AFTER you get the surface aligned as you want it.

Attachments:

• tree2_2017Sep3a.gh, 120 KB

Permalink Reply by Joseph Oster on September 3, 2017 at 10:00am

P.S.  Meant to leave 'SrfSplit' disabled; this version shows the surface and projected curves for splitting it, which is all you need while experimenting with parameters to affect the shape.

P.P.S.  I suspect you might find better shape control if you reduced the maximum value of those 'y' and 'z' sliders feeding the 'Expression' components, and make them reals instead of integers.

Attachments:

• tree2_2017Sep3b.gh, 116 KB

Permalink Reply by Joseph Oster on September 3, 2017 at 10:39am

I reduced the range of the two 'Variable z' sliders, made all four real instead of integers; reduced 'Count', and found the "Part of the Taiwan House" so located it for reference:

Attachments:

• tree2_2017Sep3c.gh, 125 KB

Permalink Reply by Joseph Oster on September 3, 2017 at 11:52am

I realized later that 'Rebuild' was also feeding the outer edge pipe, which got out of sync when I used 'Loft Options' rebuild instead.  So I modified this pink group to use the outer edge of the lofted surface for that 'Pipe'.  Other small changes...  The reduced range controls are much better tools for shaping the surface, eh?  Cool roof, by the way.

Oops, forgot to disable 'SrfSplit' again.  Too slow to use with it enabled.

Attachments:

• tree2_2017Sep3d.gh, 117 KB

Permalink Reply by Kay Kay on September 4, 2017 at 9:38am

Really appreciated for your help and corrected my scripts :)

I have successfully generate a new curve and pull down a 'control point'... as shown here. Thanks to you and Paul. 

Noticed there is a weird part of the curve at the back of the house as shown (I didn't make any changes to it previously) but seems like another 2 control points that are far away from the curve but creating an intersection? How can I fix them and make it a smooth curve?

Attachments:

• mushroom2_2017Sep4.gh, 116 KB

Permalink Reply by Joseph Oster on September 4, 2017 at 9:51am

My efforts were intended to give you more precise control of the shape by fine tuning the curves and loft rebuild params.  Adding rotation to align the "corners" is another easy step.

Moving control points to alter that shape is a whole different game.