Reducing Vertices

[Spinell]

Yup, here am I again.

AFter finally getting my mesh to show up in the uploader (weird error that I'll never figure out), no matter how hard I tried or how many hours I waited, it coulfn't calculate the price for the uploade and showed an error message.

From my experience, this is, at first, because I have way to many vertices for SL to properly calculate in one go.

I researched a few way to reduce vertice count and came across the Decimate modifiers. However, when I tried applying it... It gives an error called "no manifold mesh as input". I have no idea what this means.

I'd like to ask for some help in figure out this modifier and, if possible, more suggestions on how to reduce vertice count.

Note: I already removed doubles and turned tris to quads. Not sure what else I can do.

[hibit Spad]

In edit mode

Select > non manifold           ctrl alt shift      M

 

Basically these are places where the mesh doesn't wrap back on itself.  Like a missing face.

 

As far as the decimate modifier,  well it works but it chooses vertices based upon it's own programmed reasoning and things are not necessarily what you would want.  So trial and error with this thing is the best approach.  Make sure you save different versions (under different names) so you can go back in time if you royally mess up.

 

Look at the loop tools to help you when it comes to reducing vertice count.

 

 

 

[Spinell]

Hum, I don't know why but it's simply not working. I go into edit, select>nom manifold, then back to object mode, add the modifier, and still get the error.

[Chosen Few]

Nonmanifold geometry is geometry that cannot be unfolded into a flat surface.  It depicts impossible topology, which could not exist in real life.  It is most often a result of poor planning on the part of the modeler (no offense), and/or of the use of incompatible tools or procedures during the modeling process. 

Some simple examples of non-manifold geometry are as follows:

• Three faces, sharing a single edge, to form a T shape.
• Two adjacent faces sharing a single edge, with normals facing in opposite directions.
• Two or more faces that share a single vertex, but no edge.

Non-manifold geometry makes certain mathmetaical operations, induding uniform reductions, impossible.  This is why your decimation didn't work.  The math just doesn't jive.  It's like trying to divide by zero, can't be done.  It also may well be why SL didn't like your model.

You need to clean up your model before you can proceed.  I'm not sure what options Blender has for this.  (You didn't specifcy, but I assume you're using Bender.)  If it were Maya, I'd just tell you to run the mesh cleanup command, which among other things, converts non-manifold geometry to become manifold.  If Blender has an equivalent command, use it.

Of course, the better option, going forward, is just not to end up in this kind of situation in the first place.  Often it's simpler and far more effective just to create a lower poly model by hand, rather than look to automated procedures like decimation to do the work for you. Understand, decimation won't necessarily work very well, if you didn't build your model to be well reducible in the first place.

I'd suggest you do a little reading about retopology.  It's an important skill to develop as a modeler, and Blender has some excellent built-in tools for it.  You basically use your existing high-poly model as a scaffold, and create the new low-poly version right on top of it.  It's not a one-click solution, by any means, but once you've got a little experience with it, you'll find that even a very complex model like a full character can be retopologized relatively quickly and painlessly.  I don't know about you, but I'd rather spend an hour or two retopologizing by hand than spend days trying to clean up the mess left behind by a decimation gone wrong.

You'll also find that if you know you're going to be retopologizing anyway, it's actually very liberating during the intiial modeling stages, since you don't have to worry at all about keeping your topology clean.  You can just hammer out the sculptural form of the model with impunity.  This kind of freedom too throw caution to the wind can be an absolutely tremendous time saver upfront, which will often more than make up for whatever time you spend retopologizing afterward.

 

 

 

[hibit Spad]

Instead of going back into object mode look around at your model and you will see the non manifold vertices selected.  you can then set about fixing things if you want.

[Nacy Nightfire]

It's not enough just to press ctl alt shift M.  This only HIGHLIGHTS any non-manifold geometry by selecting it.  You have to follow this up by actively deleting the non-manifold geometry that is highlighted.  Note that its perfectly normal to have the borders of empty areas highlighted as non-manifold geometry..don't delete that.  You are looking for things inside your geometry  such as inside "bridging" faces and faces you might have created by accidently hitting E for extrude and not then translating so these faces remain as narrow as edges and hidden...things like that. 

Find them and delete them.

[Drongle McMahon]

"Note that its perfectly normal to have the borders of empty areas highlighted as non-manifold geometry."

Yes. I just wanted to emphasize that. For Blender, at least, you have to add to Chosen's definitions by treating the two faces either side of any free edge as adjacent, so that the edge is non-manifold because the normals are opposite. Even a single flat plane is non-manifold, as is the open edge loop of a cube with one face deleted. Many normal meshes contain these kinds of free edges, and there is no problem with uploading them. So it's only the other cases you need to deal with.

So it looks like Blender requires a completely closed surface with inside an outside completely continuous and normals either all pointing in or all pointing out, to call it fully manifold.