11 Replies Latest reply on Jun 8, 2013 2:15 PM by Jerry Steiger

# Handle of Spline?

What is the meaning of a dimension given at the handle of a spline as below image?

http://s17.postimg.org/a5s7gjzmn/swdim.png

Is it the length of the handle?

If yes, why the length of the handle doesn't looks like 900 and 905?

It looks too short than 900 and 905.

If no, what is the mean of this dimension?

• ###### Re: Handle of Spline?

Welcome to SolidWorks forums Harley.

It is Tangent Weighting of the spline handle. I'm not that good at surfacing or spline so can't really tell you its use. Please refer to help files to get more details.

• ###### Re: Handle of Spline?

Deepak Gupta wrote:

Welcome to SolidWorks forums Harley.

It is Tangent Weighting of the spline handle. I'm not that good at surfacing or spline so can't really tell you its use. Please refer to help files to get more details.

I am not asking its uses.

I asked what is meant by the dimension given at the handle of the spline.

I never read and heard about tangent weighting in the curves and surfaces for computer aided design (e.g. bezier curve, b-spline curve, nurbs curve).

I do read about weight of the b-spline and nurbs curve but not the tangent weight.

Is weight = tangent wieght?

The curve  is look like a quadratic or cubic bezier curve to me

If it's a quadratic bezier curve, then point B will meet at point C.

So the control vertexes are, A, B-C,  and D.

But the length of the A-B handle is 900 and the length of C-D is 905.

It (A-B and C-D) will intersects at certain points.

Then it's a cubic bezier curve where the control vertexes are A, B, C, and D.

Also, the length of the A-B handle does not looks like 900 units, it looks shorter than 900 units, too short.

Similar as the length of the C-D handle.

• ###### Re: Handle of Spline?

Harley,

As Deepak said, the number controls the shape of the spline. You can see the effect by changing the values. I have no idea what the numbers actually mean. As you noted, they certainly don't reflect the length of the handle. As I recall, they seem to change with the size of the spline. If you make a spline proportional and make copies of various sizes, I think the numbers on the handles increase as the size of the spline increases.

I don't find the numbers very useful.

Jerry S.

• ###### Re: Handle of Spline?
`Jerry Steiger wrote: the numbers on the handles increase as the size of the spline increases.  `

What size?

Jerry Steiger wrote:

Harley,

As Deepak said, the number controls the shape of the spline. You can see the effect by changing the values. I have no idea what the numbers actually mean. As you noted, they certainly don't reflect the length of the handle. As I recall, they seem to change with the size of the spline. If you make a spline proportional and make copies of various sizes, I think the numbers on the handles increase as the size of the spline increases.

I don't find the numbers very useful.

Jerry S.

All Solidworks users must be know if the dimension of the handle is changed, the spline's shape changing too.

But that not the answered I want.

• ###### Re: Handle of Spline?

Harley,

The numbers on the handles seem to increase or decrease depending on the "length" of the spline. Make a spline. Make a couple of copies of the spline. Make the copies proportional. Fix one end and drag the other end to make the splines larger or smaller. Dimension the length from one end to the other. Uncheck the "Proportional" box so that the handles are shown again. Dimension the handles. The dimension of the handles scales approximately with the dimension of the length. I have no idea why it scales only approximately and not exactly, nor do I have any idea why it scales at all.

I am a mechanical engineer. Mark Biasotti is an industrial designer. You need a mathematician to answer your questions. There don't seem to be many who post on this forum.

Jerry S.

• ###### Re: Handle of Spline?

Can someone show me the control vertex of the curve in my first post?

How to show the control vertex of spline in solidworks?

• ###### Re: Handle of Spline?

The most detail i have seen is in the presentation below , which i expect explains this much better than i can without doing a live example, this is by Mark Biasotti

http://files.solidworks.com/special-videos/everything%20curves%20and%20surfaces.zip

Mark works for SolidWorks and is "Senior Product Manager - Definition"  I know he was heavily involved in developing the surfacing and spline tools since about 2006 and has contributed alot in terms of blog posts, forum answers etc. If there isn't enough within that presentation you'll be sure to find more detail from him about everything related using the search

Essentailly (lifted from the solidworks knowledgebase)

"The tangent weighting value doesn’t directly relate to anything physical. It is a variable used to compute the parameterisation and knot values of the spline so that the software can have asymmetric dragging of the handle.  SolidWorks doesn’t publish that algorithm.

For a spline where the handles have not been asymmetrically dragged, the sum of the values will be proportional to the magnitude of the derivative at that point."

Alan

• ###### Re: Handle of Spline?

Alan Sweetenham wrote:

The most detail i have seen is in the presentation below , which i expect explains this much better than i can without doing a live example, this is by Mark Biasotti

http://files.solidworks.com/special-videos/everything%20curves%20and%20surfaces.zip

Mark works for SolidWorks and is "Senior Product Manager - Definition"  I know he was heavily involved in developing the surfacing and spline tools since about 2006 and has contributed alot in terms of blog posts, forum answers etc. If there isn't enough within that presentation you'll be sure to find more detail from him about everything related using the search

Essentailly (lifted from the solidworks knowledgebase)

"The tangent weighting value doesn’t directly relate to anything physical. It is a variable used to compute the parameterisation and knot values of the spline so that the software can have asymmetric dragging of the handle.  SolidWorks doesn’t publish that algorithm.

For a spline where the handles have not been asymmetrically dragged, the sum of the values will be proportional to the magnitude of the derivative at that point."

Alan

No information which answers my question.

Only about general curvature, C1, C2.

• ###### Re: Handle of Spline?

Sorry didn't realise it didn't mention the handle dimensions, however it does talk you through how solidworks splines work all the handles etc including tangent weighting/ other possible settings.

Am I misunderstanding or is your original question what is the dimension in your picture is it a value in mm etc?  unless i am very much mistaken as the others have said it is tangent weighting.

"The tangent weighting value doesn’t directly relate to anything physical. It is a variable used to compute the parameterisation and knot values of the spline so that the software can have asymmetric dragging of the handle.  SolidWorks doesn’t publish that algorithm"

This is from the solidworks knowledgebase.

Essentially i often use them to atleast lock downa relation to construction surface capturing or the midplade of somethin i am going to mirror. Also if you want them to be the same length you can link the values ( and prob use teh newer global variables option)

Not sure about control vertex? not a term i have come across.

Perhaps mark will be able to give some more tips/ info especially as i hear we are getting some more toys to play with in ralation to splines in 2014 (based upon SWW 2013)

• ###### Re: Handle of Spline?

Harley,

Right click on the spline. Select "Display control polygon".

Jerry S.

• ###### Re: Handle of Spline?

Is it the hermite spline?