Detecting a boundary for a not closed object

[Anonymous]

We have a few 2D Blocks with very irregular shapes. The 2D blocks are slices or projections of 3D objects clearly extracted from a different software. We are looking at calculating the area of those shapes. However, the shapes are not closed entities and our app fails to find the boundary. We even tried using hatch and adjusting the tolerance to create and keep the boundaries, but it is also failing to detect it.

The question is: Is there any development or option to detect this overall boundary when lines are not perfectly closed or overlapping? 

Thanks

[marko_ribar]

I think you are in bad situation, but have you tried "PEDIT" command "Multiple" option, "Join" and specify fuzz tolerances for gaps, for ex. 0.0001...?

If curves are overlapping too then I can't think anything better than command "OVERKILL"...

So all, in all, try combination of both commands and see if the shapes will close...

HTH., M.R.

[Anonymous]

Hi Marko,

Thanks. Yes we tried all that and unfortunately didn't work.

Thanks for your tips.

Daniel

[Scottu2]

Biagi,

If your program does not work with Splines you may have to convert them to LWpolylines.

Try the Flatten command on the objects and then use Overkill.

Adjust the Overkill command with setting of .002 instead of .000001  and mark the lower check-boxes to combine lines

(The Flatten command part of the express tools ribbon)

[hak_vz]

---

@Anonymous wrote:

We have a few 2D Blocks with very irregular shapes. The 2D blocks are slices or projections of 3D objects clearly extracted from a different softwar

Thanks

---

Area is not exclusively linked to closed boundary. As you say, your polylines are inside blocks that don't provide area information. To get area of an object inside a block (insert) use this. Just click on a boundary.

(defun c:get_blk_area( / e bo area)
    (setq e (car (nentsel)) bo (vlax-ename->vla-object e))
    (if (vlax-property-available-p bo 'area)
        (setq area(vla-get-area bo))
        (setq area 0)
    )
    area
)

It would be easier to work with sample drawing, but I hope this is what you are looking for.

[john.uhden]

@hak_vz 's offering may be very helpful

IF there is an entity like a polyline to select.

Otherwise you are probably out of luck as the getboundingbox method will always return the lower left and upper right corners of a rectangle that surrounds the object.

I wish there were a getboundingoutline method.

[Sea-Haven]

Like others here.

There is Lineworkshrinkwrap, Convex hull and a commercial product, how well they all work ? 

If they can be plines then open plines do return area.

There is area by points methods but if curves then its not accurate, arc to chords improves accuracy at expense of speed.

Really need a dwg may require explode block or may be as simple as get entity inside block.

[stevor]

One way, is to make a lisp routine that uses  the convex hull  method,

like at:

http://www.lee-mac.com/convexhull.html-- or 

http://www.realerthanreal.com/autolisp/ConvexHull3D.lsp.

[hak_vz]

Convex hull algorithm(s) are applicable only for limited group of shapes. It will not produce correct results for complex shapes, let say a star.

As long as we have to guess what kind of polylines (splines) or even line segments is saved inside block we can not offer proper solution. @Anonymous says that blocks are created in 3d party application, what means a lots of shortcut solutions.

[Anonymous]

Thanks everybody for your help.

Unfortunately I can't upload the blocks due to confidentiality issues. I will try all your advice and get back to you.

Additionally I think I will try something else: I will convert the blocks to JPG and do a trace over using the AutoCAD Rasteer Design functions (automatically). Hopefully, the polilines drafted on top of the lines will be simpler and easier for AutoCAD to detect. Some accuracy will be lost but it will hold 98% of it.

I'll try all these approaches and get back to you.

Thanks for your help

[stevor]

If Convex hulls are inadequate,  Concave hulls can be made, with much more investment.

About the same cost would be decompose, ie, separate, the 'blocks' into parts that are primitive enough to get their areas.

[hak_vz]

@Anonymous  To determine what kind of polyline object is inside a block paste following code in system console, run it and click on a line object inside a block.

(cdr(assoc 0 (entget(car(nentsel "\nSelect line object \n")))))

 I hope my code will work, but just in case it won't, at least we'll know crucial info to update code.

[Sea-Haven]

Draw something close or edit one of the blocks distorting its shape its really about no idea what you have.

Only send a couple of  blocks use wblock and pick block objects will not make much sense without text etc.

[abdullah_najm]

Thanks a lot!