Polylines

[blimey]

How could I draw curved polylines made of arc segments that would be entered by giving 3 points?

I don't get how to use the bezier, cubic etc... whan I try to be precise...

[islandmon]

Whoa ... Dude ... curvature is a world onto itself ... there realy is no end to the madness and complexities. All curvature is the result of compromise, ie. segmentations of an ideal arc. There are numerous postings about these procedures. May I suggest the VW Help and search these forums. The topic is wide open. Each tool offers a different approach to arc creation and manipulation. Therefore you will need to become familar with them by trial & error. A few hours of practice and you will be in the curve comfort zone.

[blimey]

I think my post was'nt very clear. I'm not in any 3D sophisticated things. i'm just trying to do a 2D polyline that should look like this :

So far I'm drawing 2 arcs (determined by clicking 3 points)for the curved parts and lines or polylines for the straight parts, then I combine them so that it becomes a polyline. Is it possible to draw the arcs (determined y 3 points) within the polyline mode? I only saw that I can draw curves but not arc?

[MullinRJ]

Use the U key when you draw with the Polyline tool to cycle through the types of points to be inserted next. You can correct the radii afterward with the 2D Reshape tool. If you set the Fillet Radius to 0 before you draw, the tool will insert the largest radius possible for that vertex.

You can also draw a Polygon or Polyline (corner points only) and convert points to ArcPoints afterward with the 2D Reshape tool.

And, if you need to do this a lot, you can always write a script (or have one written for you) to make a custom tool that simplifies the repetitive parts of the task.

HTH,

Raymond

[jan15]

I wouldn't use the Polyline tool to draw that thing, especially if I wanted to specify the shapes of the arcs by 3 known points. The Arc modes of both the Polyline tool and the 2D Reshape tool depend on an external control point to fix the radius of the arc, rather than using three points on the arc itself.

If I wanted a surface shaped like that, I would draw an arc-by-3-points for the larger radius arc, then offset it to get the smaller radius arc, then select both of them and issue the Clip Surface command, which uses the surface of the smaller arc to trim the surface of the larger arc (this only seems to work when both arcs have visible surfaces, i.e., when their fill type is something other than None). Then I would draw the rectangular part with the Polyline tool, or with the Rectangle tool and then rotate it and reshape one corner to meet the corner of the ring segment. And then I would select the resulting trapezoid and the ring segment and issue the Add Surface tool to combine them into a single surface.

Or I might draw a rectangle and a circle (using a temporary 3-point arc to find the center of the circle), combine them with the Add Surface command, offset the resultant surface, Clip Surface, and then use a temporary rectangle to clip the full horseshoe shape into just the part wanted. That would work even if the fill type is None.

I'm not sure either of those methods would be faster than lmt's method of drawing lines and arcs and then using the Combine Into Surface command, but there's something very satisfying about using those Add and Clip Surface commands.

[DDDesign]

Like Jan15 I'd prefer to use Add and Clip surface. To add a few point to her method:

1. To offset the second arc I like to duplicate in place (my duplicate offset pref =0) then offset the second arc radius by subtracting the amount in the OIP.

2. I don't see to have a problem with no fill in the arcs when clipping.

3. I'd prefer to straight segment with the rectangle tool, then convert it to a polygon.

4. At the end of the first method, the curved end will still be missing the end cap. This can be added by clipping the (overlength) arcs with a temporary rectagle or line. Or -

4. Select and decompose the whole object. Add a line segement for the cap. Select all elements and compose.

[islandmon]

The proof is in the pudding ...

as I was saying ... so many options .. so little time ... half the fun is trying new ways to describe simple shapes. Once we get it down to the methods best suited to our needs .. then we become set in our ways.

I would just use lines and arc by radius then convert to lines & Compose then convert to 3d Poly or NURBS.

[blimey]

Thank you for you advises. I think I'd try add an clip surface as an alternate way to mine. It seems easy. I didn't thought about clipping the arcs and it is one of vw nice tool.

[jan15]

David,

The missing end cap is just hidden from view.

All surface objects, and all polylines, are actually closed objects, but one edge may be hidden from view.

Using the 5th mode of the 2D Reshape tool, click on the midpoint of any hidden edge to make it visible. Click on the midpoint of a visible edge to hide it.

[blimey]

Jan15,

Do you know if there is a way to set the edges alwys to non hidden by default?

[jan15]

lmt,

No, I don't think there is such an option. The only edges that are hidden by default are edges that you didn't draw but which are necessary to complete a surface, so that VW has an area to fill or hatch. If you draw a polyline but don't close it, the edge that's needed to complete the fill area is hidden because you didn't draw it. If you draw an arc, only the arc is visible. The radius lines that form the other two edges of the fill area are hidden because you didn't draw them.

When I want a complex surface including arcs and straight lines, I usually start with rectangles and circles, not polylines and arcs. I move and rotate the rectangles and circles, and Add them and use other rectangles and circles to Clip them. When you work that way all edges are visible by default, because you're starting out with surfaces that have edges all around them.

[alanmac]

I think the advantage in the method Jan15 outlines in the last paragraph is that whilst to some it may take slightly longer using rectangles etc and clipping etc. at least you have a surfaces to your shape, so when extruding its a solid with no "surprises"

Of course the combine tool will work to the same effect with lines and arcs, but in my experience you only need a slight misalignment of points/lines for it to fail, and then it involves close examination to find the offending item/s.

I've never really approached VW as a program to draw lines but shapes, defined by lines.

Even after many years of productive use I'm still discovering and enjoying its potential and capabilities.

Just as you think you more or less know them all they bring out another version upgrade with even more in. ;<))

Alan

[blimey]

Yes, I'am trying to get use to clipping surface... just don't have the reflex yet. It is a nice tool

[mdarch]

a handy hint is to add the tools Add Surface/Clip Surface etc to the right click context menu, saves a lot of mouse movment

[propstuff]

quote:

---

Originally posted by mdarch:

a handy hint is to add the tools Add Surface/Clip Surface etc to the right click context menu, saves a lot of mouse movment

---

Excelent idea,

how do you go about changing it?

[Andrew Bell@NV]

The workspace editor has the context menu as one of the menus, you simply edit it like you would any other menu.

[propstuff]

Doh!

thanks Andrew