Nevertheless, there's something inherently immediately intuitive about moving points "on" the curve, as opposed to moving points that lie off your curve. Despite the fact that's their mathematical definition.

Hi Kevin,

> Nevertheless, there's something inherently immediately
> intuitive about moving points "on" the curve,

Yup, and MoI allows you to move a point on the curve with this special drag mode that's mentioned here - that mode is active when you have control points turned on but then go and drag on a spot directly on a curve rather than dragging the control points.

See this post for some more information on how to do that:
http://moi3d.com/forum/index.php?webtag=MOI&msg=744.16

The part that does not work well for editing is not so much about just moving just one point on the curve, it's about moving a point on the curve while simultaneously locking down other various points on the curve into a fixed place as well.

Locking down a bunch of other points on the curve during the edit basically forces a pivoting action to happen around them, making a whole lot of bulges and ripples in the result.

Here's an example - say you have these 5 points here:



Now if you want to move the middle point but lock the curve down to pass through all the other 4 points where they currently are, you're basically forcing the curve to pivot around them like this:




It's really difficult to control things and maintain a nice shape when editing when there are all kinds of bulges being added into the curve like that in other regions a little bit away from the one you're trying to edit - that's basically why that kind of editing is not very productive.

Manipulating just one point without trying to constrain numerous other points does not have the same kind of issues, and neither does editing control points since control points act as more of a guide for how the curve is shaped rather than over constraining it.

- Michael

Yes, an as in the solid edge version, it only HAS points on the curve ( Constraining??) where in MoI, the on curve edit picks the point you desire.. My question was related to being able to control the weight of the point that i pick, irregardless of the existing point stucture..

So I can acheive what I want by rebuilding a curve to fit the density i need for localized oncurve edits... I'll have to see how well this workflow will work, while maintaining my original curve and not reshaping it by rebuilding... However, I am really envisioning this for tracing type operation, so slight deviation from curve rebuilding wouldnt be a finished product failure...It would just make it faster to get the overall shape layed in, then refine with the low point count curve as needed...

Hi Burr, yeah I was just kind of making another example for Kevin there on how "points on the curve" can lead to problems when there are many of them being constrained at the same time.

Do you still have some more questions about the curve on point editing stuff though?

One other thing that I should mention - if you want to reduce the area of effect of the movement, another way you can do that aside from a full curve rebuild is to use Edit > Add pt to add in some more control points just in that one particular area of the curve.

So those are a couple of ways you can make the editing more localized to a smaller region of the curve. The part that is kind of harder is trying to increase the area of effect - that's what could possibly be done in the future with a multi-pass mechanism that tried to reduce changes in tangency like I was kind of mentioning earlier. It will probably take a fair amount of experimentation to get something like that to work well though.

- Michael

Hi Michael,
I was just kindof chiming in to clarify what my original request was about for the others reading... I think you had it covered though, and I didnt have anything further regarding this..

But you just made a great "point" (Pun)

The adding point "On the curve" didnt change the structure of the curve at all, whereas, adding point to the (Whatever you call the dashed line that is planar between the control points) does change the shape..

So the new question is, could the add point command have a numerical value to set? Like "add 5 or 10 points?" and then of course to reverse it would be the other part.. Would there be a workflow to be able to remove points without changeing the curve structure???

Hi Burr,

> The adding point "On the curve" didnt change the
> structure of the curve at all, whereas, adding point to
> the (Whatever you call the dashed line that is planar
> between the control points) does change the shape..

Yeah - when you click a point directly on the curve instead of on the dashed line between control points (that line is called the control polygon or maybe control polygon hull) it does an operation which is called adding a "knot" to the curve - this does keep the curve shape exactly the same and a new control point will be added in that vicinity with the control points shifting around a bit instead of the curve shape shifting around.

It's kind of easiest to do this mode when you have control points turned off so that you won't grab the control hull during Add pt, since the hull takes precedence.


> So the new question is, could the add point command have a
> numerical value to set? Like "add 5 or 10 points?"

Well, a curve has an infinite number of possible locations you could add a knot to - like when a curve has a parameter range from 0 to 1 a knot could be added at parameter value = 0.2, or at 0.255 or at 0.224 or at 0.582, etc... - it wouldn't work very well to just add in points at totally random locations so there would have to be a mechanism to control the region you were adding them in at. If you're only adding in something like 5 points, it would probably take about the same effort as just running Add point 5 times...

By the way if you do want to run Add point many times in a row set the "Repeat" checkbox to be checked before you place the first one, that way it will auto repeat and you will only need to left click to place each one and right-click at the end to stop.

Needing to add in a whole lot of points like 10 at a time to a localized area of a curve in a repeated and regular way is kind of unusual - I guess I'd need to see some examples of how that would be helpful to understand that better.


> and then of course to reverse it would be the other
> part.. Would there be a workflow to be able to remove
> points without changeing the curve structure???

No, not really - I mean there is such a thing as "knot removal", but it's only in certain special cases that it can be done without changing the shape of the curve at all. It could be done to ones that you added in with "Add point" (with the Adding a knot method), but just any general curve like points that you created by drawing a control point curve are not possible to remove without altering the shape of the curve.

- Michael

Hi Michael,
Ok I see. My questions have come from a lack of understanding about that structure of a b-spline...

When I originally did this add point (Knot), I thought I saw the "entire point structure of the sample curve shift" to reflect the added point.. After your last post, i realized it was just a local shift of points!!!

So with this, it kindof answers my questions because I can see that once the point structure has been changed, you could probably just reverse the knot input and acheive the reversal, but not (Pun) if you alter the curve..

BUT, this also gives me a better result than i was originally looking for with the on curve editing and "rebuilding" method, as I wont need to revert the points to be less dense..

When I need more localized on curve movement, I can just add some knots to that area and get it, and leave the rest of the curve in original low density!!

Thanks for that!

I suppose then that in that original "Solidedge 2 point structure" method I was talking about, with the control hull points and the points on the curve showing and movable, that the points on the curve were just representations of "Knots??"

Hi Burr,

> I was talking about, with the control hull points and
> the points on the curve showing and movable, that
> the points on the curve were just representations
> of "Knots??"

Yeah, that could be, but there is also another possibility that it's showing you something more like a history of the curve with the original points that were interpolated to draw it (it only has a "through points" draw method, is that correct?) . If that's the case then editing a point is not actually so much editing the curve but rather creating a brand new "through points" curve using those points - creating a whole new curve like that is slightly different than actual curve modification methods.

Do the "points on the curve" show up for curves that you've imported from other programs or only on ones created inside of Solid Edge?

Or it could be a kind of hybrid - showing knot locations for imported curves where the construction history was not known, and showing points to interpolate for curves that were drawn right in SE...

- Michael

By the way, in the future I do want to show "points on the curve" for the case where you built a curve using the "Through points" command in MoI - making editing that particular kind of curve more like a history edit with a replay of that command instead of an actual editing of the curve. But there would also be some option to turn that off and use its control points as well.

- Michael

""""""""""But there would also be some option to turn that off and use its control points as well.""""""""

Or "BOTH".... :)

I dont have solidedge.. I was just referencing that as an example, so I cant really test how it is handeling all the situations...

But, You've answered a good workflow for me...

Both at the same time isn't very good because they edit the curve in different ways - it would be ok for just dragging one single point of either type but building up a multiple selection of points that included some "on curve" points and some regular control polygon hull points at the same time and then doing a transformation on that multiple selection would not make sense.

- Michael

Hi Michael, this is what originally sparked my interest...

http://youtu.be/g-Q_jaqg5fc

You can just go to 4:40 of the video and look for about 30 seconds to see what i was refering to...

But I like MoI's with the "pick any point" on the curve better....

Hi Burr, I suppose those are probably knot locations being displayed on the curve.

But notice in the video that with the 2 kinds of points displayed at the same time he only ever drags on a single point to do the edit? (or at least in that particular spot of the video).

Moving just 1 point is fine for many situations, but it can also be useful to grab a whole set of control points with a window select and move all of them in one operation.

But doing multiple selection of both kinds of points (both "on curve" points as well as control polygon points) is going to be problematic because each kind of point needs to do a different kind of edit to the curve, you can't do both types of editing at the same time.

Maybe they do something arbitrary like just ignore edit points if there are also control points selected or something like that - but it tends to be far better to avoid having ambiguous situations in the first place.

- Michael

> But I like MoI's with the "pick any point" on the curve better....

The nice part about it is that you can tweak any part of the curve that you want to, rather than only being able to grab certain locations...

- Michael

I was thinking that you had said that only showing one or the other and not both at the same time, as in the video. But now that you bring that up, I can see how this could be problematic with "selecting an oncurve point along with a hull point" at the same time.... Good note..

Thanks again for looking at this.....

related with all this :)
Does it possible to "join" a point to a curve even this last is moving when control points of the curve are moving?
Actually a point is not "joined" even you uses the command "join" !

Hi Pilou - the Join command knows how to join curves together into larger composite curves or surfaces together into multi-face or solid objects. There is no functionality in Join for joining a point to anything else.

I guess you want to have a kind of "Persistent point on curve" - a point that is located at a particular parameter value of a curve and moves with the curve when you edit it? MoI does not currently have anything set up for that.

- Michael