# so, what is manifold geometry

 10 October 2003 henning New Member Software Developer so, what is manifold geometry So far, I've been able to determine the following: Non-manifold geometry is when polygons are arranged in weird ways. For example, take an hourglass and pinch it in the middle so that the geometry there goes down to one vertex at that spot. The whole hourglass is now non-manifold. But... what's the definition of manifold? And how do you check if geometry is manifold or not? henning share quote
 10 October 2003 ajk48n Frequenter   portfolio Adam Katz Freelance 3d Animator/Motion Graphics Designer Sydney, Australia It is geometry that can't be unfolded into a flat piece. Examples are two polygons next to each other, with normals facing in opposite directions, two planes that share a single vertex but no edge, and two polygons, with the edge extruded outward from the edge that both share (basically making a "T" shape out of 3 polygons). share quote
 10 October 2003 playmesumch00ns Lord of the posts   render monkey pretty picture maker United Kingdom m __________________ You can have your characters photoreal, fast or cheap. Pick two. Last edited by playmesumch00ns : 10 October 2003 at 09:08 AM. share quote
 10 October 2003 DogmaD Lord of the posts   Victor Legerstee Graphics Programmer Netherlands Manifold models are models where the volume is well defined. They have the following properties: Every edge belongs to two faces. Every vertex is surrounded by one sequence of edges and faces. Faces only intersect eachother in common edges en vertexes. There is a material on only one side of a face Another way of putting it, a manifold object is a shape that you can create in real life. non-manifold objects have qualities, where you have badly defined volumes in your shape, making it impossible to recreate the model exactly that way in real life. Hope it helps.. share quote
 11 November 2003 DaKrunch Know-it-All   portfolio Davide Pesare Artist wrangler Pixar Animation Studios San Francisco, USA curiosity: a box without a face (5 square faces and a hole) is non-manifold? i guess the answer would be the same as for a plane? thanx __________________ Davide Pesare There are only 10 types of people in the world — those who understand trinary, those who don't, and those who mistake it for binary. share quote
 11 November 2003 DogmaD Lord of the posts   Victor Legerstee Graphics Programmer Netherlands Yeah, thats non-manifold. The object contains no volume, because it isn't a closed space. share quote
 11 November 2003 markyjerky Frequenter I'm suspicious ... I'm suspicious ... That a lot of programs would not go through the rigor of trying to detect if a surface intersected itself in strange ways into order to qualify or disqualify something as a manifold. In other words ... I bet with 9 or of 10 programs that want to operate only on manifolds, as least 9 would not care about how visually twisted the model is ... so long as the topology (which has nothing to do with the strictly visual) remains that of a manifold. Just some thoughts. since we are talking about manifolds. share quote
 11 November 2003 DogmaD Lord of the posts   Victor Legerstee Graphics Programmer Netherlands Well, no they should check. One of the constraints/properties of a manifold object is that faces should only intersect eachother in common edges or vertexes. So this is not only a topologic demand, but also a geometric demand. I don't know how most programs check for this, but there must be some fast check to satisfy this property. share quote
 01 January 2006 CGTalk Moderation Expert Thread automatically closed This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum. __________________ CGTalk Policy/Legalities Note that as CGTalk Members, you agree to the terms and conditions of using this website. share quote

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts vB code is On Smilies are On [IMG] code is On HTML code is Off CGSociety Society of Digital Artists www.cgsociety.org Powered by vBulletinCopyright ©2000 - 2006, Jelsoft Enterprises Ltd.