Sketcher Spline Functionality - NURBS Anyone?

[ptc-2889084]

We would like to see sketcher implement NURBS in addition to its current spline functionality. I understand that a project is being considered for implementation in Creo 4.0, probably March 2014. Requirements are needed in the next several weeks. At the moment, we are developing our requirements to send to PTC. The requirements will probably be both descriptive and mathematical.

Some random thoughts: Should be able to support current constraints. Ability to extract and manipulate using TOOLKIT. Be able to set NURBS parameters; e.g. as degree.

What requirements do you have?

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[James62]

I am not really sure if anything of this is implemented inside of Creo already. I don't bother sketching splines and compound curves in Creo since I am better of doing that in Rhino but what I would like to see in Creo is:

1) Ability to control sketcher spline curves with aproximation points, not just with interpolation points.

2) Ability to move the curve control points by specific distance and in specific direction, not just freely

3) Ability to automatically reconstruct any curve. Change its degree and number of points while showing the shape of the new reconstructed curve and shape of the old and compare their biggest distance before confimation of the reconstruction (check Rhino rebuild command and meaning of maximum deviation).

4) Ability to apply curvature continuous connection to the sketched spline.

[MatsLindqvist]

1-2) Isn't this already possible? If you double-click a spline you can switch from "interpolation points" to "control points"... You can check out the attached pictures; 4 different ways of dimensioning spline. You can change to a dimensioned spline, but not back again it seems...

Don't know for sure about 3-4. If I remember correctly, you can create a spline datum curve through points with curvature control at the endpoints, i.e. not use sketcher to create a curve. Or apply curvature constraints along edges in a blended surface, that attaches to other already existing surfaces.

/Mats Lindqvist/Econocap AB/Sweden/

[James62]

Mats Lindqvist wrote:

1-2) Isn't this already possible? If you double-click a spline you can switch from "interpolation points" to "control points"... You can check out the attached pictures; 4 different ways of dimensioning spline. You can change to a dimensioned spline, but not back again it seems...

Thanks. It get's tough to handle the splines with dimensions as the points constraint themselves with each dimension added so off hand it's possible to move multiple points only in one direction (either horizontal or vertical).

[Constantin]

3. is partially possible with the "Curve from Curve" command inside "Independend Geometry" (former "Scan Tools" license). Any curve can be reconstructed by either number of points or within a tolerance with endpoint constraints, including a deviation plot. This works for both 2D and 3D curves.

4. it is possible to create a curvature continuous spline to a reference outside the sketcher by using the "Equal" constraint "=" by clicking on the reference and the spline near the reference:

[James62]

Constantin wrote:

3. is partially possible with the "Curve from Curve" command inside "Independend Geometry" (former "Scan Tools" license). Any curve can be reconstructed by either number of points or within a tolerance with endpoint constraints, including a deviation plot. This works for both 2D and 3D curves.

Ok, that would be really helpfull in sketcher.

Constantin wrote:

4. it is possible to create a curvature continuous spline to a reference outside the sketcher by using the "Equal" constraint "=" by clicking on the reference and the spline near the reference:

That never worked for me. Equal always adds equal lenghts of entities like tangent lines of sketcher curves etc. But maybe I am doing it all wrong.

[Constantin]

Concerning 4:
I just checked and it also works with entities from the same sketch BUT it only works connecting a spline to an arc or line...

[ptc-2889084]

This is what we would like to see for a NURBS implementation within sketcher:

1. Be able to use all existing constraints.

2. Allow tangency at both ends.

3. Check box for spline attributes: uniform/non-uniform, rational/non-rational, continuity (1st, 2nd degree), curvature.

4. Be able to build NURBS from one or more construction entities in sketch (e.g. line, arc, line)

5. Optionally display control points, knots, and weights.

6. Allow user to move NURBS by: dragging on curve, modifying control point(s), knot(s), and/or weight(s)

7. Specify length.

8. Position points along curve either by length or parameter.

9. Parameterize in family table.

10. Using TOOLKIT/Object Toolkit, create NURBS in sketcher.

11. Allow for callbacks/listeners to impose user defined constraints on NURBS.

12. Create family of "scaled" curves; one end fixed, other end displaced vertically by specified amount.