Very Computer

by **Defee Paw** » Mon, 17 Aug 1998 04:00:00

Hello,

I am trying to construct a winged-edge representation of a mesh with Euler
operators, given a mesh in the "simple" form, i.e. vertex list and list
of polygons with indices to the vertex list.

Most winged-edge source code references on the net refer to Ian
Ashdown's public code package, so that is what I am using. He provides the
following operators:

BOOL JoinEdgeKillVertex( WEdge *, WEdge *, WVert * );
BOOL KillEdgeFace( WEdge *, WFace * );
BOOL KillEdgeVertex( WEdge *, WVert * );
BOOL KillVertexFace();
BOOL MakeEdgeFace( WVert *, WVert *, WFace *, WEdge **,WFace ** );
BOOL MakeEdgeVertex( WFace *, WVert *, Point3 &, WEdge **, WVert ** );
BOOL MakeVertexFace( Point3 &, WVert **, WFace ** );
BOOL SplitEdgeMakeVertex( WEdge *, Point3 &, WEdge **,WVert ** );

Now, my concern is how do I use those operators to easily construct my
winged-edge representation of a mesh from the standard vertex and polygon
lists? I took a look at the original Baumgart papers from the 70's, he
does explain the operators thouroughly but I am still completely missing
the info on using them in mesh construction.

It seems to me as if I needed adjacency and membership relationships ( =
topology data) in order to construct the winged-edge representation.. but
that is why I am constructing it in the first place, to have access to the
topological data :).

I am sure everyone dealing with winged-edges has done this before, so any
help is appreciated.

Regards,
Pawel Defee
--
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Pawel Defee

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by **Craig W. Reynold** » Tue, 18 Aug 1998 04:00:00

> I am trying to construct a winged-edge representation of a mesh with
> Euler operators, given a mesh in the "simple" form, i.e. vertex list
> and list of polygons with indices to the vertex list...I took a look
> at the original Baumgart papers from the 70's, he does explain the
> operators thouroughly but I am still completely missing the info on
> using them in mesh construction.

(BTW: Pawel probably already knows this, but Bruce has a nice site
with online versions of some historical papers plus links to the
excellent Stanford ELibrary which contains scans of other old papers:
http://www.Baumgart.COM/BGB_home_page.html)

Quote:> It seems to me as if I needed adjacency and membership relationships
> ( = topology data) in order to construct the winged-edge
> representation.. but that is why I am constructing it in the first
> place, to have access to the topological data :).

> I am sure everyone dealing with winged-edges has done this before,
> so any help is appreciated.

The winged-edge representation is great way to store the adjacency and
topological information once you know it. But first you need to
obtain it by laboriously searching through the information-poor vertex
and polygon list. For example, the edges in the winged-edge database
can be found by enumerating each pair of adjacent vertices listed on
any polygon. To find the two polygonal "wings" for a given edge, you
need to find the two polygons that contain the edge's two vertices
(which will be listed in opposite order) and so on.

If you need more detailed help with this searching step, I can put you
in touch with Larry Malone, author of N-Geometry (aka S-Geometry, see
http://www.nichimen.com/PRODUCT-INFO/nworld/geo/geo.html) who has
written similar translators.

Craig Reynolds
http://hmt.com/cwr/

Very Computer

Mesh construction with Euler operators (& winged-edge)

Mesh construction with Euler operators (& winged-edge)

Mesh construction with Euler operators (& winged-edge)