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View Full Version : How to use the knife-function in 2D-Polygons

rdeutsch
14th November 2006, 11:02 AM
Hi

I'm here the first time and want to say hello. I use the AC3D to build sceneries for modelflightsimulators.

But now i have a problem:
I have a polygon and 3 small polygons inside.

http://www.roebeli.ch/images/rde/knife.jpg

Now i need to cut out the regions of the 3 small polygons.
Can anyone explain me how i can do that with the "knife"-function or are there other ways?

Thanks and best regards
Robert

Andy
14th November 2006, 12:31 PM
Welcome Robert.

There are usually many ways to make the same stuff.

Try making a 3x7 mesh and deleting the 3 surfaces.

rdeutsch
15th November 2006, 02:38 AM
Hi Andy

Sorry, but how can i make a 3x7 mesh?

Regards
Robert

luuckyy
15th November 2006, 03:07 PM
Hi rdeutsch,
this is what Andy is talking about :

http://img245.imageshack.us/img245/7163/image2qo1.jpg (http://imageshack.us)

You will have a black and white mesh just after its creation.
It's just 2 different materials applied to the mesh.
If you want a single material for the whole mesh then just select all the surfaces and apply a single material
to them (#1 in my case).

Regards.

rdeutsch
16th November 2006, 02:51 AM
Hi luuckyy and Andy

I tried that but the result is not very impressive. :(

I can use the knife-function only when the knife-object is a 3D-model, as a 2D-polyon it doesn't cut anything.
So here are the steps i made with the 3D-polygon, but as you can see, the knife does not cut all parts:

http://www.roebeli.ch/images/ac3d/k1.jpg
http://www.roebeli.ch/images/ac3d/k2.jpg
http://www.roebeli.ch/images/ac3d/k3.jpg

Do i something wrong or is there another way?

Thanks and regards
Robert

Dennis
16th November 2006, 04:03 AM
I think Andy's original suggestion was to create the 3x7 mesh and skip the knife altogether. This is probably the best approach for what you're trying to do (the knife isn't built to cut out interiors, only make slices along edges).

The idea is, you would remove the surfaces you didn't need from the 3x7 mesh. You could then resize each of the rectangular holes by manipulating the vertices directly.

Stiglr
16th November 2006, 08:32 PM
I think the general idea here was to make a 3 x 7 polygon because, if you count the number of spaces and shapes from top to bottom you get 7 "rows", and side to side, counting the border and the three shapes, you get 3 columns.

After making that basic 3 x 7, just move the vertices (in X and Y only) to the positions they need to go to describe the polygons, and then eliminate the "intervening" areas. If necessary, perhaps add vertices between pairs if there aren't enough to perfectly describe the shapes.

It's very simple. You just need to begin to think like the program, if that makes any sense.

coldby
17th November 2006, 04:37 AM
Hi rdeutsch,
Andy is right, of course: he's probably the only one in the world who knows everything about AC3D. But as such he sometimes tends to forget that things aren't always as easy as they look to him :)

Try the following: