Great to see a detailed discussion of technical issues here, (makes a change from drama!) though I have to say that at present much of what is being discussed is a bit over my head. I want to get into creating in mesh, having been a prim builder for a long time (I still build with prims, but increasingly appreciate where mesh is superior) but most tutorials are really truly bad (boy some people can waffle!) confusing and offer no real support. Inworld classses ar an option, of course, but not always suitable due to timezone differences. At one time Aine Caoimhe's excellent 'Baby Steps' tutorials used to be available, but are now behind a restricted access on her Blogger page. I've not seen any other Opensim/SL specific tutorials anywhere, and what I particularly liked about Aine's tutorials is that they were written in an accessible way and were straightforward to follow, and started with the fundamentals, such as setting up the Blender interface so that it was better suited to Opensim creation. I remember discussing this with Aine, and discovering that we both were a bit 'old school' when it comes to instruction, and much preferred a long-hand written approach to (often very poorly made) video tutorials.

Would there be any chance of there being some basic, introductory tutorials here on OSW so that more of us could get into legitimate content creation, whether that's from scratch or adapting the huge amount of content that is liberally licenced.

My technique is to start with the blender script that removes doubles, and cleans up illegal geometry. That is always my first and last step. Almost will load after that, except an object with no triangles. I have not found a way to find those except to hide each object. and anything left, that are just a dot I delete. There has to be at least one triangle for all 4 LODS, and since there are none it will abort and you will never figure it out. Luna's problem is very common when you use the viewer to make LODs. It can reduce a part below one triangle. One other loader issue if 8 materials max. Thats easy to fix in Blender, select the object and click Ctrl V (Vertex) and separate by Materials. The viewer will struggle with high counts of linked objects, so many meshes is better then one big bunch of mesh. It will rez much quicker too.

Please don't use the analyze button. it makes bad physics mesh where you cannot walk through doors. This has been known and cautioned by developers for many years. You get convex hull and you cannot make it physics type None or physics type Prim. Then you probably make it phantom and then use prims (ugh, they are always 96 triangles) to fix it.

I prefer to make a custom physics model. I start with a plane for a house floor, which is 2 triangles. That one sided mesh becomes my floors and walls (when I want walls). I extrude it to make ramps too, so stair steps are walkable. It is one object, and very low poly.

I rarely use the physics model settings in the viewer. I would say except for avatars, which only use two LODs, it is 99% cubes for me.

I rarely load anything except cubes as the physics model in the physics tab. It was intended to load a physics model directly. That is very difficult to do as the viewer requires a minimum of one triangle at the min/max X, Y, and Z of the model. That's why you always see cube models the same X,YZ size in preview. That really is painful, and really obsolete. If you can't get it just right, your physics gets enlarged or shrunken. And I don't want physical things hanging out there to trip over or fly into.

I load the model using the many cubes technique. One way is to load 100 cubes into blender and export that and then load it as a physics Object in the physics tab. But now the Latest Firestorm has this built-in. Assuming all your mesh objects have less then 21,000 triangles it should load in a few seconds.

Now up load the custom physics model on high physics and it will be in in a second. It's a simple set of planes.

Set that in place and walk on it. Select all of the main model, and make it physics type = None. Now link it to the physics model so the physics is last. It will remain type - prim. Now you have a very low poly physics model, that uses up the least amount of RAM and the least amount of precious CPU. And unlike prim shims on bad mesh, your house is one obect. You can take with you without leaving the invisible physics model behind.

One other trick to bring in very large models is use the cube at 0,0,0, in blender. Brink in chunks of your mesh along with the cube. That way you can zero in on the problem mesh and get it fixed. Use the arrows in the viewer x,y,and z coordinates to position each chunk you upload correctly by aligning cubes. It will be accurate to .01 meters

Very informative Mari, My go to is Deviantart many 1000's of models and ideas. Oh not to mention a handy script loaded into blender is always a huge help and a folder with many different physics models needed for the Big stuff :).

Thanks Marianna for the great article! Sketchfab is my go-to website, for both free and paid items, when I'm looking for mesh components to add to my primarily prim builds. After trying multiple download file types, I find that I prefer GLTF 2.0 when available. And as Marianna noted, taking the time to truly assess your mesh will prevent issues uploading.

I mostly use Blender 4.0, and the primary tools I use are Merge Distance, Decimate, and Smart UV Maps. If a mesh comes with textures and uv mapping, I use only merge and decimate to preserve the original map. If there are no textures, I will join all the pieces into one object, merge distance, decimate, then create a new uv map. I also use Blender 2.79 for baking normals on highly detailed mesh objects, like statues. here's a good video on that process: https://www.youtube.com/watch?v=0r-cGjVKvGw

The key step I use when exporting to collada is to uncheck the Triangulate box in the popup menu under Operator Presets / Geom, otherwise you might get the dreaded 'Vertex number more than 65534' error. If I get a physics is missing error, I will try other LOD levels before going back to the drawing board in Blender. If I get a 'Dae Parsing' error, I go back to Blender and make sure all faces are facing out and not flipped. Here's a good video tutorial on identifying and correcting those: https://www.youtube.com/watch?v=NT_ozJW8v50&list=PLIyBt3CA...

As for physics, I use the latest Firestorm viewer and tend to use a variety of approaches, depending on how the user will interact with the mesh. If it's just to be seen, I'll select a low or medium level LOD then select 'cube' or make a similar basic object in Blender to encompass the mesh. If it has a high vertex number and it's something that will be up close and interacted with, especially furniture, I will select at least the medium physics option then apply the analyze tab. If the upload already has a very low vertex number to begin with, I will change all the LOD's to match the high setting and skip the analyze step altogether.

These of course are just my preferences and are not being promoted as the only way or best way to approach some meshes. Other creators will have their tips and tricks and preferred ways of handling mesh. Hopefully, some of this will be helpful.

Thank you for sharing this. It is very informative. I have often wondered how this process would work and you explain it clearly. Plus i learned that "retopologize" is a word!