CAD files - straight segments

[The Vector Doctor]

I don't have any dedicated CAD software. Why do CAD programs create curves as a series of short straight segments instead of genuine smooth curves? Is there a setting in the software?

If someone creates a CAD file and it has straight segments instead of smooth curves can they change a setting after the fact or must it be created as such from the beginning?

When I create a file in Illustrator and export the file as a DWG or DXF file the resulting file does in fact retain smooth curves. So I know these 2 formats support curves. Is it the CAD program that is the issue?

I have a customer who received a file from someone else that is incredibly complex and if they can go back to the person who did this in their program maybe there is a setting they can change and avoid having it recreated

 

[J Hill Designs]

well I know when outputting dxf from omega there is a bezier curve conversion in the options that changes it from line segments, minimum arcs, and maximum arcs...maybe something like that is in autocad

 

[rfulford]

I think there are a lot of cad programs out there that do not support curves but the main one, AutoCad, definitely does support curves. That being said, I see this problem with dxf files exported from autocad regularly.

 

[tsgstl]

I would love to know the answer. It is less of a problem with printing now, but I used to either save it as a JPG then vector it and hope for the best. Or I have had success outlining and bringing it back from the outline. Some of these files can be made up of tens of thousands of lines and freeze flexi when doing anything.

 

[signage]

From what i remember about CAD that has to do with the setting of Polyarc and polygon! I do not remember which one you want though!

If memory serves me right it should be set to polyarc for smooth curves!

 

[J Hill Designs]

From what i remember about CAD that has to do with the setting of Polyarc and polygon! I do not remember which one you want though!

my guess would be polyarc

 

[LittleSnakey]

If exporting from autocad save as a version 12 dxf file to preserve the curves. all other versions change the arcs to straight segments. One other trick is to set up a printer in autocad that uses hpgl language and save the plot file.

 

[Dave Rowland]

it has always been an issue, to add to this Corel Draw actually has very poor DXF/DWG conversions.

Two ways I solve this:-
In the past I used a bit of software that came with Gerber Advantage, it was an EPS/DXF conversion routine. It did a great job of importing and sorting out between EPS(ai/corel) to decent cutting format (DXF)

the second and the way I do it now is using the Vectric software on our CNC machine, Vectric uses EPS formats to import so transferring between Corel to Vectric works and then I could Export to DXF from Vectric if i needed to.

I did test loads of programs and even tried to write my own routine, I came to the conclusion that the curves that we use within Corel are very hard to convert to Arc's within DXF, so the easy option is to make hundreds of short lines.

 

[The Vector Doctor]

ok i will keep the polyarc function in mind for future reference, thanks

 

[rjssigns]

One thing that you MUST ALWAYS DO is use the regen command. It's function is to smooth arcs. If you do not use it your files will look like poo.
('specially running a laser for vector output, ask me how I know)

And no, I do not have a clue as to why arc smoothing is not automatic in a mega-dollar program like AutoCad.

 

[signmeup]

I haven't used my cad program for quite a while but I do remember Corel was not good at importing DXF. I suspect Ai is even worse. Not sure you can blame the draftsman on this one. I think it's a translation problem.

 

[The Vector Doctor]

I haven't used my cad program for quite a while but I do remember Corel was not good at importing DXF. I suspect Ai is even worse. Not sure you can blame the draftsman on this one. I think it's a translation problem.

doubtful. I have seen drawings that did not get imported and they had the same issues

 

[signmeup]

doubtful. I have seen drawings that did not get imported and they had the same issues

Ahhh. Didn't know that part.

Corel always reversed my drawings and made the lines into little segments.

 

[James Burke]

I'm using ACAD 2000i and Adobe Illustrator CS5 and it doesn't appear to be an issue...even when saving an ACAD file that hasn't had a REGEN, all my arcs come in smooth. AutoCAD and Illustrator (and SignLab) work together extremely well together.

Have somebody with Illy import the same file and see what kind of results they get.

Also see if your customer can combine the segments as a "joined" PEDIT (polyline edit) or a REGION.


JB

 

[Techman]

Older Autocad files exported curves as line segments. I do not know about the latest Autocad.

With that said...
It has nothing to do with Corel importing the files wrong. Almost all CAD softs import Autocad DFX with line segments because that is the way they were exported.

Most program that export DFX use the autocad standard thus export as line segments..

However. DFX Tools for Corel will fix that problem. It will import line segment dfx files into corel and export them as ARCs. Arcs is what is needed to get the proper curves.

http://www.coreldrawtools.com/professional/index.html

In fact jemmyell a member here is the author of this very nice utility.

 

[signage]

DXF is an autocadd format for Drawing Exchange Format. This has been an issue in cad for a long time.

 

[Custom_Grafx]

My combo;

Autocad 2007
AiCS4

Anything but a polyline comes into Ai fine (curves preserved - usual Ai curve handles).
A curve drawn with the pen tool, exported to DXF, when opened in my AutoCAD, is also properly recognised as a spline.

My guess is that your customer has converted their arcs or splines into polylines before sending to you.

Reason: Certain manufacturing processes (some CNC machinery) cannot understand arc and splines. Before production all such elements need to be exploded or flattened in order to reach non curve polyline format. This way, the CNC machine can just work off lines.

Summary: If you have a client working in CAD, tell them to draw in arcs and splines, and to leave them as such.

 

[Fenda333]

Smoothness

I have AudtoCAD 2002 and here is how I work that out....

Tools Tab
Options
Display Tab

The 'Display Resolution' box in the top right hand.

The 'ARC and CIRCLE SMOOTHNESS' is what you want.

I set mine to 1000 and don't have a problem. Usually the preset causes the segmentes arcs to save on memory and allow for faster panning, etc.

Also, REGEN will make it look nice on screen but it should plot the same either way, regen'd or not.

At least this is my experience over the last 11 years.

Hope it helps