Offsetting composed objects

[Stefan]

Hey i have an accuracy problem here. I have made a rectangular shape with radiused corners and one corner taken up with a large arc. I want to offset to the inside of the shape, but when i do so, it seems to get chunky almost. It's like it converts everything to lines, and not arcs. (i export it and it IS a bunch of lines)

Here's a test that proves my point. Draw an arc or a half circle, and draw some lines coming off each end point. Now compose the three objects, and offset a distance to the inside. The resulting arc/circle is now a grouping of lines shaped like an arc. I hope there's a different way of doing this and im doing something wrong.

My objective is to get this offset as smooth as possible because im exporting to a CNC machine program that is not impressive, and yet it would do a better but slower job of this drafting. Any help would be greatly appreciated. Thanks.

[Guest]

GO to File Preferences and under the Edit tab see what you have set for the 2d resolution.

What is set here?

When you "export" it - what file format are you exporting it as?

Why aren't you drawing a rectangle and using the fillet tool to arc the corner?

[ 05-06-2003, 05:27 PM: Message edited by: Katie ]

[P Retondo]

For some reason, when a polyline (the result of the compose command) is offset, it becomes a geometric approximation in the form of a polyline comprised of straight segments. Mathematically, there is no reason a simpler and more accurate result could not be calculated, so I have always been puzzled as to why this shortcoming of the offset tool persists. I work around it by decomposing, then offsetting the separate elements, and composing again.

[Guest]

It should always create a polygon object.

Make sure the 2d resolution is set to high or very high before doing the offset. The offset object will appear completly different depending on the original shape and the 2d res. settin.

With the 2d res. set to high or very high - are you getting anything other than a polygon?

Even though an arc may look like lines .. it may not be. THe screen resolution may not be able to draw the perfect smooth arc on the screen.

[P Retondo]

"It should always create a polygon object"

Katie, when you say "should" I think you are talking about the designed behavior of the offset tool. We aren't disagreeing that this is how it works. Actually, we are complaining about how it works! Using "should" in a different sense, it would be better and more useful if the offset tool created another polyline with a parallel geometry. I.e., if the polyline originally consisted of two straight segments with an arc in between, the offset polyline "should" also consist of two straight segments with an arc of a different radius in between.

To be technically succinct, the problem I see is that the result of offsetting a polyline object is always a polygon object. We would need to extend the scope of the offset tool so that the result could be a polyline in order for it to do what is desired. If we could start by making this work at least for arc elements, that would be fairly easy and very helpful. Bezier and cubic curves would require more math.

[Guest]

Gotcha

I'll add it to the wish list when the new list is available for me to input.

[Az Gecko]

I have to echo these same complaints regarding the offset tool. I have this same problem when offsetting (which I never had using software by the EVIL EMPIRE). I tried setting the offset to Very High and got a line with 7 vertices that was not even close to the offset desired (the shape is a pool, and the offset was a 2' line, whats up with that?). I than set the resolution to low and did get a 2' offset, but it had 169 vertices and looked like 169 line segments trying to look like the 15 arcs used to create my shape. Since designing pools and decks is the butter for my bread I'm a bit frustrated with this feature.

[Guest]

Can you send me the ouline form of the pool wiht the offset parameters being used?

tech@nemetschek.net?subject=ATTN:Katie

[Stefan]

Sorry i took so long to reply Katie. As for what is set under the preferences, it was on low, and by setting it to very high, it did improve how it 'looked' but when i export it (dxf/dwg) it would still be quite a bunch of segment lines. All it did was increase the number of them, so in theory it still isn't accurate.

Last thing i want is for my CNC router to do all those small little lines. And so i leave the offsetting to the "inferior" program, still.

I wholeheartedly agree with P Retondo, so i do hope this issue gets improved. In any case, thanks Katie.

Got a question. Um, since this is a vector based program, why would the offset be like this? And, why hasn't this issue been addressed in the past 10 versions of vectorworks?!

[ 05-09-2003, 04:30 PM: Message edited by: Stefan ]

[P Retondo]

Stefan, have you tried using the set of small lines as output to your router? It might be worth a try, since your CNC software is going to convert the arc to little small lines anyway to create a set of target points for your router's path. That's how all CNC control software works. The only problem might be if your control program converts to much smaller segments.

[Stefan]

Yeah, i know were talking about a sandpaper stroke or two here, but its the thought that counts

I however do know the CNC runs on curves because when we're hard coding it, we do a start coordinate, end coordinate and radius. But if i were to use these curves exported by vectorworks, all it would require would be a little touch with sandpaper, if that. No biggie. I guess i always gripe when cut product is a millimeter or two off.

[ 05-09-2003, 07:48 PM: Message edited by: Stefan ]

[P Retondo]

Stefan, the path planning part of the CNC software takes curves as input, but converts them to straight line segments when it outputs to the machine. All CNC devices work this way, and the faster and better their computing systems, the shorter the length of these line segments.

[Stefan]

Hmm, interesting.. guess i learn something every day. What kind of experience do you have with CNC routers?

[P Retondo]

My experience is academic (mechatronic control and integrated manufacturing). We worked with a variety of milling machines and general control devices. I know about the way these systems (hardware-software interfaces) work because we had to design and implement them as part of our academic work, but I couldn't help you with any detailed information about CNC routers per se.

[Guest]

I've been discussing the offset issue with the developer.

As soon as I get more information, I'll let you know.

[GT123otto]

Another point of view... I work with complex polylines and would like to use the offset feature to help define geometry for 'cutter diameter compensation'.

My work around is to offset the polyline. Then I go thru the polygon to manually insert arcs using 3 point snap points. Then I delete all the short lines. This keeps my file size down to a reasonable level... which helps recalculation & redraw times. A gillion little lines also bog down subsequent 3d modelling.

Please, please make the offset tool insert arcs. It would save alot of time.

Thanks

[Guest]

Now that you have been studying the offset tool so, how about an offset tool in vectorscript that actually works? I've built one that is very robust and about 90% accurate. I'd like to get one that is more reliable. The offsetpoly tool doesn't duplicate an object with an offset instead it offsets the existing poly by the given dimension. This is not what we need. We need a real offset tool!!!!

[Kees W]

any news on this front? I've found myself having to offset a lot of free-form shapes to create walls, and the subsequent gazillion points in the offset makes it impossible to alter the shape after the offset/clip surface procedure.

very annoying indeed. Was this adressed in VW 11?

Or was anyone ever succesful in creating a plugin that does work?