Boundary command

[PGia]

Hi
I’ve run into this problem several times, but I was never able to understand why — until today.
Sometimes I need to use the "boundary" command to obtain the perimeter of complex enclosed areas, but occasionally the area of the region returned by the command does not match the expected value.
Today, I finally discovered why.

In the image, I show an example of this. The thick yellow line is part of the original geometry, while the thinner dark-colored line is the one returned by "boundary".
I repeated the command several times, but it always makes the same mistake.
Does anyone understand why this happens?
Is it possible to solve it somehow?

Thanks in advance.

[BIGAL]

No idea what the thick yellow line is ?

 

If its a pline with a width then boundary is correct, it does not recognise pline thickness. I am sure there is ways to make a outline of the plines can then run boundary.

 

If it's a hatch then can get outlines of hatch's then should be able to do a boundary.

[hmspe]

https://lee-mac.com/polyoutline.html  or  https://lee-mac.com/advpolyoutline.html  will outline a pline.  https://jtbworld.com/autocad-hatchb-lsp

 willoutline a hatch.  I can't tell what might be required to automate the process without a DWG of a full pline set or hatch set example.

[PGia]

I think I didn’t explain myself properly.

The idea is to run "boundary" and click inside the largest closed area shown in the image.

After checking the result — by zooming into the area indicated by the arrow — you’ll understand what the image in my previous message is referring to.
I’ll attach a drawing.

Boundary.dwg

[hmspe]

So the problem is that the darker lines should intersect in the top square glyph instead of the next to the top square glyph?

 

Which CAD are you using?  When I run BOUNDARY or HATCH here in Bricscad V26 the boundary is always to the upper square glyph, not to the next to the top square glyph as shown in your drawing.

 

What are the parameters you are using for the BOUNDARY command?  

 

Do you get the same error if you explode the plines before you run BOUNDARY?

[mhupp]

Must be an AutoCAD thing works in BricsCAD. you could just join the other 3 polys and get the same effect.

 

Edited Saturday at 08:46 PM by mhupp

[PGia]

I’m using AutoCAD 2015.
"boundary" is supposed to return a perimeter exactly matching the geometry surrounding the point specified to the command.
I run the command using the option to identify boundaries by 'pick' on screen.
I haven’t tried exploding the polylines into lines yet.
I’ll give it a try, but I suspect the result will be the same.

[ronjonp]

AutoCAD 2027 still has the bug:

[SLW210]

Worked fine on my home computer with AutoCAD 2000i, but I get the same as @PGia and @ronjonp on AutoCAD 2026 at work.

[mhupp]

Does it create a closed poly? or is it open where the two lines don't meet.

[Danielm103]

creates a closed polyline in Autocad 2027

 

Edited 17 hours ago by Danielm103

[marko_ribar]

@Danielm103

Why Properties palette doesn't show how many vertices does closed polyline have? That was always included AFAIK if I can recall correctly...

[Danielm103]

8 hours ago, marko_ribar said:

@Danielm103

Why Properties palette doesn't show how many vertices does closed polyline have? That was always included AFAIK if I can recall correctly...

Not sure, you can hit the current vertex and iterate backwards, mine showed 228

[PGia]

I exploded the polylines into lines. I also reduced the lineweight to 0, but in both cases the result remains the same.
A colleague who still has an old PC with Autodesk Map 5 (= AutoCAD 2002) also confirmed that the same error occurs.
If I’m not mistaken, AutoCAD 2002 is basically the same as AutoCAD 2000, so @SLW210’s statement that the "boundary" command works correctly in that version intrigues me.

[mhupp]

I reversed all the polylines see if that does anything.

 

-Edit

Might fix it on the bottom but then mess it up on the top.

 

Rervers Boundary.dwg

Edited 6 hours ago by mhupp

[mhupp]

1 hour ago, Danielm103 said:

Not sure, you can hit the current vertex and iterate backwards, mine showed 228

 BricsCAD is showing 230  61+119+53 - 3overlapping points.

  

Edited 6 hours ago by mhupp

[lastknownuser]

This has been talked before if I understood the problem correctly: https://www.cadtutor.net/forum/topic/61468-boundary-precision/
To create a boundary you have to have the whole area visible in your model, everything needs to be visible in display area
So it has to do something with your "viewing resolution" (zoom), that's how command works. What is the limit I don't know, I never did tests like they did in topic mentioned above. But I also had the same problems with large areas like you posted, when I have one short line, or polyline segment, one of the boundary vertices would be wrong (bad precision).
The solution for me was to create lisp working with regions, then convert region to polyline. When creating regions you don't need to see the whole area on your screen, you select the lines and its just pure math from there