Topological explorers

There are at least 3 different topological explorer classes: TopExp_Explorer,
BRepTools_WireExplorer, and TopoDS_Iterator. Is there documentation that
describes when it's appropriate to use each one? Can they be used
interchangably? If I use BRepTools_WireExplorer to iterate
over the edges in a wire loop, are the edges returned in the proper order
and with the correct orientation?

Thanks,
Blair Downie
downie@simmetrix.com

Rob Bachrach's picture

The differences are not documented in any one place. However, you
can get the gist of it by reading the documentation on the individual
classes:

- TopExp_Explorer explores all the subshapes of a shape, but allows
you to filter on finding or avoiding particular types (see the
examples in the documentation). This is great if you are looking for
a particular type. This actually uses a TopoDS_Iterator internally.
If you are looking for a particular type of shape, this is the way to
go.
- TopoDS_Iterator more generally visits all subshapes of a shape. You
can optionally get those shapes with the location and orientation
fully applied. This is useful if you wish to visit all shapes of a
shape and is especially efficient if you don't care about the location
or orientation.
- BRepTools_WireExplorer returns the edges in a wire in the proper
order for traversal. Please note there are limitations when
the wire is not a closed loop and when there are singularities (see
the documentation for details).

blair_downie's picture

Rob,

Thanks for your reply.

So does this mean that I must use BRepTools_WireExplorer if I need to
traverse the edges in a wire in the proper order?

Rob Bachrach's picture

Unless you re-write the code yourself using other explorers and
looking at common vertices, yes. Please note the limitations
however. Unless your wire is a closed loop (such as around a face),
WireExplorer does not bolster confidence. If it is a closed loop,
it works pretty well.