Attach Spline

famadorian

I'm not seeing how to attach a spline to another spline. Am I blind?;)

TimRice

Are you referring to splines in the sketch environment? or in an assembly? Feel free to share a link to your document and we can take a look.

famadorian

In this image, I've got a spline and I want to attach it to the next spline, such that the two splines are connected and the result is one spline. 

TimRice

You could try using the tangent sketch constraint in order to make the spline flow along with the rest of the curve. To do so, select both the spline and one side of the curve and select the tangent constraint. Then repeat for the other side of the curve. Also, it appears you have a three spline with three inflection points. You should be able to get away with only two.

Here is a video on sketching constraints that might be worth a watch: https://www.onshape.com/cad-blog/tech-tips-constraining-your-sketch

famadorian

You're answering something different here. I want to make the 3 splines into 1 spline. 

TimRice

Would you mind sharing the link to your document? This way I can take a look at the doc directly and it would help me understand the problem better.

famadorian

I could do that, but I don't understand the reason;) I just want to connect two splines into one spline; how much simpler can you get?

famadorian

Here's a video displaying how to connect two splines in Maya. 

https://www.youtube.com/watch?v=J4BnFlojBIs

I don't know in any simpler terms to convey what I want to do. This is not rocket science. I want to make one single spline out of two splines; that means I have to connect one end of a spline to a beginning of another spline. 

robert_morris

I think the confusion may be from not knowing why you need to turn them all into a single spline.

If it is for creating a solid or surface using tools like Extrude, Sweep, Loft, etc., then there is no need to convert them into a single entity. All those tools can use multiple curves to create the feature.

If it is so that you can have all the control handles work together to edit the shape of the curve, then that is a different matter.
For that, there is no built-in way (that I am aware of) to convert them into a single spline. You would be better off just using a single spline to begin with and adding more control points where you need them. 

It also may be possible to create a Featurescript that will take multiple splines and convert them into a single one.

øyvind_kaurstad

You can add points to a spline in Onshape, but you can only position those points, you don't get handles to control the spline curvature at the point, which is a shortcoming IMO.

I also fail to understand why the OP wants to merge splines. You can make splines coincident (and tangent if needed) at the ends, which is more or less equivalent.

robert_morris

øyvind_kaurstad,
You are correct. I was mistakenly remembering the splines in SolidWorks, which did have handles on the control points.

lana

@esben_stien
 The short answer is : Onshape currently does not have merge spline functionality. Please create an improvement request.

famadorian

Do we have a bug tracker for Onshape?

NeilCooke

@esben_stien you can create an improvement request (this is not a bug because it is working as intended), using the feedback option under the help menu.

famadorian

So, there is no public enhancement tracker, then? That other guy, øyvind, talked as if attaching splines were something really special; you feel the same about attaching surfaces? I mean, attaching splines and attaching surfaces is something we do all day long in NURBS modeling. So, it's the other way around, I don't understand how he can ask a question like that, if I really want to attach splines. It's beyond me..

NeilCooke

esben_stien said:

That other guy, øyvind, talked as if attaching splines were something really special...  attaching splines and attaching surfaces is something we do all day long in NURBS modeling...

Parametric modelling is not the same as NURBS modelling, it is something completely different. In parametric modelling you get all the benefits of being able to control your entire model using dimensions and geometric references. Please submit an improvement request using the feedback option under the help menu. Another option is to model all your NURBS geometry in Maya and import it into Onshape for further editing.

lana

Onshape does not have a well developed free form surfacing functionality yet. As Neil mentioned, reconciling parametric modeling requirements and free form functionality is not a simple task. We would appreciate an insight into your workflow in NURBS modeling packages and, if possible, examples of surfaces you build. One important question : should Onshape provide the low level tools other NURBS packages are providing or should we focus on a higher level solutions? What controls over free form geometry would you like to have?

famadorian

Well, surfaces I build are mostly not parametric. I model terrain, roads, etc and very complex surfaces, like recreation areas. I want Onshape to offer these low level tools, ofcourse, cause I want to use Onshape and I do what I do. 

lana

@esben_stien
Thank you for your reply. I hope you don't mind if I ask further questions - I'd like to understand you use case better. Do you need to model terrain as NURBS (vs. polygonal mesh) ? If so, - why? How road is different from a sweep? Could you please provide pictures of models where you needed low level control in order to achieve the shape you need? 

famadorian

lana said:

@esben_stien
Thank you for your reply. I hope you don't mind if I ask further questions - I'd like to understand you use case better. Do you need to model terrain as NURBS (vs. polygonal mesh) ? If so, - why? How road is different from a sweep? Could you please provide pictures of models where you needed low level control in order to achieve the shape you need? 

Not sure what you mean; I provided a picture in the beginning of the thread of how I wanted to attach a spline to another spline; now this spline comes from some other work, so I need to attach this specific spline to others which would make up a surface. This is quite basic work, working with NURBS. Here's a video of someone working in Rhino, attaching and detaching splines:

https://www.youtube.com/watch?v=9_voQevw9T0

This is basically how you work with splines and surfaces. You create a cage of splines, then you create surfaces, until you eventually makes it a solid.  

NeilCooke

Ah I get it now. Terminology us parametric buffs are not familiar with. For all others in the thread this is the equivalent of the SolidWorks sketch tool called fit spline which best fits a single spline through a number of sketch entities. After all, to create a single spline, it must be fitting a spline in the background. 

This is a useful feature to keep your patch structure simple. You will still need to create an improvement request in the category on the right. In the meantime you could try the fit spline feature at onshape.com/featurescript 

owen_sparks

NeilCooke said:

...In the meantime you could try the fit spline feature at onshape.com/featurescript 

Hi Neil.  We have a native one of those now don't we?

Owen S.

NeilCooke

@owen_sparks no it's not the same thing. The 3D fit spline is just going through vertices whereas you can use this requested feature to turn lines and arcs into splines for smoother surfaces. 

owen_sparks

Sorry I meant the new native 3d fit spline does the same as the old featurescript fit spline so no need to to use the FS.  Is that not the case?

NeilCooke

@owen_sparks yes the new feature just does an opFitSpline. What the OP is requesting is more like what the FS feature does. https://cad.onshape.com/documents/4921880a2a6769256992599d/w/9ca359dbf967f3795856383a/e/3ce1f9c3b9012af4970f7490

famadorian

Reading this: https://www.onshape.com/cad-blog/whats-new-in-onshape-04-13-17

So, we can now attach surfaces, but not attach splines?

NeilCooke

@esben_stien there is a big difference between the two. Merging surfaces just makes those surfaces share a common edge. What you are asking for is an approximation of two or more splines.

famadorian

ok, so when do you intend to support "approximation of two or more splines."?;)

NeilCooke

Can you create an improvement request? It has to come from a customer to bear any weight. 

There is a custom feature called fit spline that might help you in the interim. 

billy2

esben-

You can write it, 

https://forum.onshape.com/discussion/5311/fit-spline

I wrote it a while back and the code is open source.

Also, as Phillip pointed out to me, you can pick a sketch with 2 splines as a guide vs picking the splines. Requires the sketch to have only 2 splines defined.

Also, I'm not sure I'd concatenate a bunch of splines into a large curve. I tend to keep these things simple. I guess it's a preference.

rune_thorsen229

robert_morris said:

I think the confusion may be from not knowing why you need to turn them all into a single spline.

If it is for creating a solid or surface using tools like Extrude, Sweep, Loft, etc., then there is no need to convert them into a single entity. All those tools can use multiple curves to create the feature.

If it is so that you can have all the control handles work together to edit the shape of the curve, then that is a different matter.
For that, there is no built-in way (that I am aware of) to convert them into a single spline. You would be better off just using a single spline to begin with and adding more control points where you need them. 

It also may be possible to create a Featurescript that will take multiple splines and convert them into a single one.

One reason to combine splines is to allow using the offset tool