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Thread: '2D polyline' & 'polyline' What's the difference?

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    Default '2D polyline' & 'polyline' What's the difference?

    Hi

    I've got a combination of two types of entity - '2D polyline' & 'polyline'.in a dwg.

    For some reason they display different context menus when I select them & right-click.
    They were created the same way I think, individual lines joined using pedit.

    I've got the PLINETYPE system variable set to 2 so they're all optimized to 2d.

    When I use the CONVERT command it converts the '2d Polylines' into 'polylines'. Which is what I want.

    However, I still don't understand how I created the '2D polylines' & why , having PLINETYPE set to 2 it didn't convert when I reopened the dwg.

    I still don't understand what the difference between the two is. They have no Z values & are in the world UCS plain, just at different elevation, which, as I understand it, doesn't make any difference.

    Any ideas?

    Thanks for your help.
    Cheers
    Dave F.

    AutoCAD 2012 Structural Detailing SP1 & Revit Structure 2012 32bit
    Win 7 32bit

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    If you draw a simple polyline (i.e. LWPOLYLINE) it's just a "polyline" in the properties box. If you then spline the line from the PEDIT command, it turns the normal LWPOLYLINE into a POLYLINE (listed) and shows up as a "2D Polyline in the properties box. I assume AutoCAD does this so it can perform different operations on each entity???

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    Quote Originally Posted by Coolmo View Post
    If you draw a simple polyline (i.e. LWPOLYLINE) it's just a "polyline" in the properties box. If you then spline the line from the PEDIT command, it turns the normal LWPOLYLINE into a POLYLINE (listed) and shows up as a "2D Polyline in the properties box. I assume AutoCAD does this so it can perform different operations on each entity???
    Thanks for the reply.

    I must have done something else because I wouldn't touch splines with a barge pole.
    Cheers
    Dave F.

    AutoCAD 2012 Structural Detailing SP1 & Revit Structure 2012 32bit
    Win 7 32bit

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    I attach an example.

    Apart from the the entity name (& the location, obviously), can you spot the difference?

    AutoCAD (well, specifically ADT) treats them differently.

    Thanks
    Cheers
    Dave F.

    AutoCAD 2012 Structural Detailing SP1 & Revit Structure 2012 32bit
    Win 7 32bit

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    Certifiable AUGI Addict Robert.Hall's Avatar
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    Default Re: '2D polyline' & 'polyline' What's the difference?

    Interesting point here......I didn't know there was another type of polyline.

    I agree, splines are nasty!

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    the're not really SPLINEs as in the entity SPLINE but splined polylines. I use them all the time when drawing out contours but make sure I break or trim them down so you actually get all the grips of every point inside the polyline. I NEVER leave anything splined... causes too much trouble.

    Looking further into a 2D polyline and LWpolyline when they're listed, you'll notice that each vertex of the 2Dpolyline has its own Handle (in addition to the entity's handle) whereas the regular LWpolyline only has one handle as the entity handle. I assume that all polylines use to be 2Dpolylines back in the day (R14) and when they came out with the LWpolyline to save space, they noticed they still needed the properties of the 2Dpolyline to perform splines and such on them. The last part here is pure speculation on my part though

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    Thanks Coolmo, your right about the handles.

    I'm aware I can use the Convert command to change them to lwplines, but I'm still confused how I created them in the first place. <I need a 'scratching head' emoticon>
    Cheers
    Dave F.

    AutoCAD 2012 Structural Detailing SP1 & Revit Structure 2012 32bit
    Win 7 32bit

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    FWIW, PEdit/Fit and PEdit/Spline turn a LWpolyline into a 2D Polyline (not a Spline) by curve-fitting.
    John B

    "You can't convince a believer of anything; for their belief is not based on evidence, it's based on a deep-seated need to believe." - Carl Sagan

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    Are these new plines or could they have been traveling through your drawings since before LWPOLYLINEs? Old school Polys, not converted, would show up as 2D Polylines (I think). They could have also come from another company or something.... no telling what "the other guy" is using or doing.

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    Default Re: '2D polyline' & 'polyline' What's the difference?

    Quote Originally Posted by Coolmo View Post
    Are these new plines or could they have been traveling through your drawings since before LWPOLYLINEs? Old school Polys, not converted, would show up as 2D Polylines (I think). They could have also come from another company or something.... no telling what "the other guy" is using or doing.
    They were freshly created by me by pediting bog standard lines.

    You're correct about the the old polylines showing as 2d polylines.

    I'm not convinced the plinetype variable works.
    AFAIK, if 2D polylines are 'old school' (even if they don't show a Z value) they should be converted to optimized LWplines (which display as polyline) with plinetype set to 2.

    Have you got it set to 2? Did it convert when you opened the example I posted?
    Cheers
    Dave F.

    AutoCAD 2012 Structural Detailing SP1 & Revit Structure 2012 32bit
    Win 7 32bit

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