Can I cut the outer side of a polygon with the cutpolya?

[yongler]

Can I cut the outer side of a polygon with the cutpolya command? I want to keep the inside of the polygon and trim off the outside of the polygon. How to do it?

[Gerry Leonor]

cutpolya?

doesn't sound like an ArchiCAD command.

[yongler]

It's GDL  command.

CUTPOLYA n, status, d,
x1, y1, mask1, ..., xn, yn, maskn [,
x, y, z]
[statement1
statement2
...
statementn]
CUTEND

Similar to the CUTPOLY command, but with the possibility to control the visibility of the edges of the generated polygons. The cutting form
is a half-infinite tube with the defined polygonal cross-section. If the end of the cutting form hangs down into the body, it will cut out the
corresponding area.

status: controls the treatment of the generated cut polygons.
1: use the attributes of the body for the generated polygons and edges,
2: generated cut polygons will be treated as normal polygons.
d: the distance between the local origin and the end of the half-infinite tube.
0: means a cut with an infinite tube.
maski: similar to the PRISM_ command.
maski = j1 + 2*j2 + 4*j3 + 64*j7, where each j can be 0 or 1.

…… …… 

But there is no status code to determine whether the cutting is on the inside or outside

[Barry Kelly]

CUTPOLYA uses mask values similar to PRISM_.

So try adding a hole (mask -1) to it.

So basically you will be making a hole inside a hole that hopefully won't cut the inside.

I am not sure it will work, but worth a try.

If not you will have to use CUTPLANEs.

Barry.

[yongler]

It doesn't look good. It seems that we can only use cutplane.

This is a defect of GDL, and the option of cutting the inner or outer sides of cutpolya should be added.

cutpolya  8  ,1, 0 , 
   -2 , -2 , 15 ,
   2 ,  -2 , 15 ,
   0 , 2 , 15 ,
   -2 , -2 , -1 ,  

   -0.8 , -0.8 , 15 ,
   0.8 , - 0.8 , 15 ,
   0 , 0.8 , 15 ,
   -0.8 , -0.8 , -1  

prism_   5 , 0.1 , 
           -3 , -3 , 15,
        3 ,  -3 , 15,
        3 , 3 , 15,
         -3 ,  3 , 15,
         -3 , -3 , 15
cutend

[Jochen Suehlo]

It works, yes, but it depends on the direction of the points given in. I am not sure, which is the working direction. (You are moving from left to right, try the other direction, which is mathematical positive)
Another way would be to use 2 half Cutpolys.

[Barry Kelly]

Sorry it didn't work.

I guess looking at it, normally with a PRISM when you cut a hole.

The connecting points are hidden inside the prism and you only see the whole in the centre.

But because you are connecting across a hole, you see the connection, and a hole inside another hole really makes no sense, which is probably why it doesn't work.

I just tried reversing the direction of the points as Joachim suggested, and had no luck.

So CUTPLANEs or 2 CUTPOLYs it will have to be.

Or you could play around with GROUPS.

One group being a large outer PRISM_ with a hole the shape of your polygon.

The other inner group the polygon elements.

Then subtract the outer group from the inner group.

Barry.

[Jochen Suehlo]

I looked at my script, which was working some years ago and made some tries.
It seems that what I said is a bit different:
Attached a working script:

PUT 1, 1, 15, 
1, -3, 15,
-3, -3, 15,
-3, 1, 15, 
1, 1, -1,

- 0.5, - 0.5, 15,
- 1.5, - 0.5, 15,
- 1.5, - 1.5, 15,
- 0.5, - 1.5, 15,
- 0.5, - 0.5, -1

!ADDz - 0.1
!PRISM_ NSP/3, 0.1, USE(NSP)
!DEL 1
CUTPOLYa NSP/3, 1, 0, GET(NSP)

! ......................... !

PUT 0, 0, 15, 
-2, 0, 15, 
-2, -2, 15,
0, -2, 15,
0, 0, -1

ADDx 0
PRISM_ NSP/3, 0.1, GET(NSP)
DEL 1
! ......................... !

CUTEND

Here I first moved the outer contour from left to right and then the inner contour from right to left.
The commented PRISM_ is for to see what shape the Cutpolya has.

[yongler]

The GDL component has been made using CUTPLANE. This allows you to freely drag and drop hotspots, freely design various shapes of exterior windows, and have a choice of 4-6 edges.

[yongler]

I have found a better way to use CUTFORM.

The status code of CUTFORM allows for the selection of whether cutting is done externally or internally.

Thank you all. 😊