'A closed boundary could not be determined' when creating hatch (possibly bug)?

[Anonymous]

Hi,

I have an issue with creating a hatch in an image, whereby Autocad claims that 'A closed boundary could not be determined' but I cannot find any problem with the drawing.

I managed to reduce it to a very simple case (in attachment). If you create a hatch in the bottom part of the rectangle, it cannot find a closed boundary, but from the top part it can. As you can see from the properties, the line is connected to the arc, so there should be no issue. I have tried the usual remedies (FLATTEN, HPGAPTOL...) but to no avail. When I make a very small modification (e.g. extending the line very slightly), the hatching does work.  It seems very strange that with such a straightforward drawing, the hatching should fail. 

I'm seeing this issue in a lot of similar drawings so I would like to find the root cause of this behaviour (and not just a workaround for this drawing).

Does anybody have any suggestions as to what may be wrong?

Thanks a lot in advance for any ideas and kind regards.

[imadHabash · Accepted solution]

the issue will fix if you redraw the arc and make sure that is connected with the line . also be sure that you're CAD elements be always located near to 0,0,0 . 

[rkmcswain · Accepted solution]

Not strange at all if you've been doing this for years. AutoCAD has always struggled with hatching where there is a sharp interior angle like that involving a curve, and with reverse curves.  xxxxxCAD hatches it with zero issues.

Moving your geometry closer to 0,0 isn't going to fix it, and neither is redrawing the arc. If there truly was a gap of significance, it wouldn't hatch the top portion either (the *same* geometry is forming part of the border of each shape)

There is a tiny, tiny, gap in between the endpoint of the line and the endpoint of the arc (inside the box), but this is not what's causing the problem. 

The problem is where the arc meets the box at that tight angle. If you draw a polyline first, on top of this geometry, and select this polyline as the entity to hatch, it works every time. 

[beyoungjr]

Hi,

@imadHabash points out a good but brief solution.

I want to show you how to identify the problem...

• Your drawing is initialized on a metric template and your objects are VERY tiny (.6268mm x .3472mm).  Hatch scale itself would be a challenge in this small space.
• Your objects are also located VERY far from the X,Y origin (3082.0274mm) to the lower left corner of the rectangle.
• If you perform a Zoom->All you will see that the tiny object set is far from the origin.
• If you select your object set and scale it by 1 million times, using the lower-left corner of the rectangle, you will be able to zoom in and see the disconnect between your line and your arc.  You cannot observe a measured distance at 4 decimal places so change your units precision to 8 place decimals and use the DI command to measure endpoint of line to endpoint of arc.  You should now be able to observe .00000050.

If you are experiencing problems with Hatching routinely then you need to correct your methods of creating your objects.  You must ensure accurate connections are made and use the appropriate object snaps when working.

Also understand the spacial sizes and relationships for your desired units of measure.  Working too far from the origin can be tough, especially on such tiny objects and using hatches that have to generate inside of such tiny objects.

Hope this helps,

Blaine

[beyoungjr]

Redrawing the line and arc accurately absolutely fixes the problem and hatches without error on top and bottom, even without scaling the model up.  The fill pattern (ANGLE) is too dense to view and I couldn't really determine a workable scale for it or the ANSI31 pattern.  You may or may not get a warning dialog about the desnsity of the hatch pattern, which offers you the decision to use a solid fill.

The place where arc meets box is not a tight angle (48°) but a tight space due to size.

[rkmcswain]

All of that is irrelevant, because the hatch works fine on the top shape. If the minuscule gap mattered, it would matter on the top shape also.

Of course if you scale the objects times one million, you're going to find a more noticeable gap, because you're magnifying a tiny error a million times.

The center of this geometry in this drawing is roughly 2525,1765. This is not "very" far from the origin. We work in state plane coordinates where the X and Y are in the tens of millions and only then do you start to see the effects of being far away from the origin with the floating point math. Even if this were a valid argument, moving this geometry close to 0,0 does not fix the problem in this case.

Lastly, other CAD programs hatch this same area in this same drawing with no problem at all. The problem is not the geometry, it's the code in AutoCAD unfortunately.

@beyoungjr 

[beyoungjr]

Irrelevant huh?  That's not how I have seen you play typically???

Re-creating the arc and line with accurate connection works, without scaling as I stated.  Please try it before shooting this down.

I gave "all of this" irrelevant info so the OP could understand his/her problem and I RARELY suggest other CAD programs or their abilities in solving stuff here.

I only reinforced the distance from origin thing because it occurs to me that the OP is not practicing a level; of design that might avoid the problem.

Please try what I offered.

I can't understand how AutoCAD succeeds with the top and not bottom and it surely is a code issue but I am only interested in showing the OP where the problem is and how to negate it.

Very Respectfully,

Blaine

[beyoungjr]

Without a single change to the file as posted by the OP...

Using the endpoint grip on the arc you can drag the arc endpoint upward and then drag it back to reconnect at the line endpoint.  The Hatch then works for top and bottom.

This is a rough design technique but demonstrates the absolute need for proper connection.

The Gap Tolerance setting should aid in the Hatch process without changing this objects but it does not in this case.  The "Gap Tolerance" may be a reason other CAD apps allow the fill to work??