Question re constraining two curves  1-20  21-25

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 From:  bigseb
4555.1 
Please see the attached model. All the green curves are to stay as they are. The red curve must be tangent to the 'straight' green curve (in front view) and tangent to the green 'curved' curve above it. How does one do this?

Thanks
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 From:  bemfarmer
4555.2 In reply to 4555.1 
Deleted

EDITED: 27 Sep 2011 by BEMFARMER

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 From:  Michael Gibson
4555.3 In reply to 4555.1 
Hi bigseb - the red curve would need to be modified in order to be tangent to the upper green curve.

Instead of modifying the existing red curve, it's probably easiest to use the Blend command to construct a curve that has the tangency you need.

To do that, trim the upper green curve at the point where you want the new curve to start, you can use the "Add trim points" button in the Trim command to specify a point on the curve for where to cut it.

So after that you would have an arrangement like so:



Select these 2 curves:



Then run the Construct > Blend command to build a blend segment that is tangent between both of them:



- Michael

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 From:  BurrMan
4555.4 In reply to 4555.2 
Do you mean like this?

EDITED: 19 Jun 2012 by BURRMAN

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 From:  BurrMan
4555.5 In reply to 4555.4 
Arc-tan command. Pic the bottom end of the red arc then the top end, then over to the green arc looking for the tan-tan snap and pick, then point at the arc you want and clcik.
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 From:  bigseb
4555.6 
That is so cool. Thanks!!
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 From:  Marc (TELLIER)
4555.7 In reply to 4555.3 
Hi,

It would be nice having some kind of automatic trim on 2d objects while using blend.
The user could specify start and end point on curves in a dynamic manner, the reference curve would then be trimmed.

It would be very useful to explore shapes and less of a try and miss with trim.

Marc
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 From:  Michael Gibson
4555.8 In reply to 4555.7 
Hi Marc,

> It would be nice having some kind of automatic trim on 2d
> objects while using blend. The user could specify start and
> end point on curves in a dynamic manner, the reference
> curve would then be trimmed.

Any idea for how the workflow would function?

Are you talking about adding an extra step to all uses of Blend where you would need to specify the points to blend from? I guess that would probably mean extra steps for the case that Blend currently handles which is blending from the end of the selected curve...

- Michael
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 From:  Marc (TELLIER)
4555.9 In reply to 4555.8 
Maybe it could be done without adding extra steps.

Blend could work the way it does now but if you click a certain distance (5% maybe) from the endpoint this would be the starting point.

Left and right sliders could make adjustments to those points or you could use direct controls in the viewport to adjust start curve and target curve contact points.

The sliders and controls would not appear if you click near an endpoint.

If you don't adjust any of these the command would work the same way.

Would this make some sense?

Marc
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 From:  Michael Gibson
4555.10 In reply to 4555.9 
Hi Marc - I think a slider mechanism would be problematic - if you want to place something at a particular point on a curve it is generally better to be able to pick that point using the point picker, that way you get to use things like object snaps to do it precisely.

If you only had sliders to use then you wouldn't be able to get an exact point like a point marker or intersection with another curve or stuff like that.

- Michael
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 From:  DannyT (DANTAS)
4555.11 
I like the sound of this and Michael, yes, picking the end points and draging them along the curve, like the loft point adjustment, would be a nicer way to go, also how difficult would it be to auto trim at that point and still retain history.

Cheers
~Danny~
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 From:  Michael Gibson
4555.12 In reply to 4555.11 
Hi Danny, actually I had been thinking that you'd need to do some kind of separate point picking stage in there, I hadn't thought about having the points draggable but that could be a good way to handle it without needing extra steps.

What about controlling which direction the blend is going in though - for a point somewhere internal to a curve it's possible for the blend to come off in either tangent direction from that point, not necessariliy just in one direction like it makes sense for with the end of the curve...

Maybe a click instead of a drag on one of the points would reverse the direction, that's kind of how Loft works as well - in addition to dragging a seam point in Loft if you click on a section curve while in Loft that section flips direction.


> also how difficult would it be to auto trim at that point and still retain history

Hmm, I'm not sure about adding trim in, would you expect for it to always do the trimming or are you talking about needing some other way to control that as well?

- Michael
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 From:  DannyT (DANTAS)
4555.13 In reply to 4555.12 
Hi Michael,

> What about controlling which direction the blend is going in though

Wouldn't the parent curve govern which way the blend goes depending where you drag or pick the point, like if you're blending to a 180° arc once you've gone past the 90° quadrant point the blend would change direction, wouldn't it ?

> would you expect for it to always do the trimming
> or are you talking about needing some other way
> to control that as well?

Always trim once you've decided on the position and commit the command.

-
~Danny~
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 From:  Michael Gibson
4555.14 In reply to 4555.13 
Hi Danny,

> Wouldn't the parent curve govern which way the blend
> goes depending where you drag or pick the point, like
> if you're blending to a 180° arc once you've gone past
> the 90° quadrant point the blend would change
> direction, wouldn't it ?

That would then make blends like this not work:



If blends somewhere internal to the curves rather than at the ends are allowed, I'm not sure that it makes sense to restrict everything from one half of the curve to only go in one direction...


> Always trim once you've decided on the position
> and commit the command.

Seems kind of risky to me - what if you wanted to build more stuff off of the original curves...

Here's an example - say you wanted to make 2 blends off of the upper arc, connecting to the curves below:



Doing too much stuff automatically can sometimes cause problems like that.

- Michael

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 From:  DannyT (DANTAS)
4555.15 In reply to 4555.14 
Hi Michael,

> That would then make blends like this not work:

Ok I see, I was thinking something closer to the end I didn't consider that situation, then you would need a flip button or a click in space to flip the blend.

> Doing too much stuff automatically
> can sometimes cause problems like that.

I see what you mean, you always come up with different scenarios, I guess that's your job :) The trim idea was just a fleeting thought, it sounded good at the time.

Are you actually considering enhancing curve blend or are you just open for ideas?

Cheers
~Danny~
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 From:  Michael Gibson
4555.16 In reply to 4555.15 
Hi Danny,

> Are you actually considering enhancing curve blend or
> are you just open for ideas?

Well, always open for ideas and if an idea allows for new functionality while not really adding any complexity to the UI (like not requiring extra stages or steps or things like that), then I tend to like to bump the priority of working on it up.

Now that I go back and read Marc's message again, I see he wrote about "in viewport" controls which I think means the same kind of point dragging that you mentioned I just didn't understand it initially.

Having draggable points for relocating the blend seems like it falls in that category (low UI overhead) well - it's similar to how Loft works like you mentioned. Similarity to other commands is good and it could fit in with the current "Adjust blend parameters" stage, so it wouldn't require a new stage to be added to the command, so that's also good.

Right now in curve blend, at that last stage if you click in the viewport on one of the blend inputs it will flip the blend to the opposite side of the curve, maybe that part could be removed if you could locate the blend starting point by dragging it.


The part about throwing trimming in as well seems not quite as promising initially - that seems like it could have some side effects. I suppose the side effects could be mitigated by having a checkbox option to enable the trimming or not, but then that option would be kind of weird to see when blending from the ends since it wouldn't do anything for that case...


- Michael
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 From:  Marc (TELLIER)
4555.17 In reply to 4555.16 
Hi,

It would be quite awesome to be able to drag points to relocate the blend!
The click to reverse feature sounds great.

For the trim aspect, maybe it could just trim and keep both side of the curve?

Also there could be some visual indicator suggesting there can be an interaction possible there, maybe points could appear at both ends of the blend...

Marc
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 From:  Michael Gibson
4555.18 In reply to 4555.17 
Hi Marc,

> Also there could be some visual indicator suggesting
> there can be an interaction possible there, maybe points
> could appear at both ends of the blend...

Yup, that's what I was thinking - that would again be similar to how Loft works currently when lofting between 2 circles. Points are displayed at the seam locations where you can drag them to update them.

So that would make sense for Blend adjusting as well.

Still not sure about automatic trimming though.

- Michael
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 From:  Marc (TELLIER)
4555.19 In reply to 4555.18 
I was thinking about this and it could be cool to have these interactive points in 2d fillet also.

Marc
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 From:  Michael Gibson
4555.20 In reply to 4555.19 
Hi Marc,

> I was thinking about this and it could be cool to have
> these interactive points in 2d fillet also.

Unfortunately that's probably pretty difficult - curve fillet currently works by calculating the result from 2 curves and a radius value. Trying to drag one point to manipulate the curve fillet would probably involve some kind of reverse calculation from that which would involve writing a completely new solver.

- Michael
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