Mesh Building - Physics \ Analyze ?

[Sokoda Soulstar]

Right.

Before anyone says "search" or something, I have searched, which is where my current knowledge originates from.

So I've been working on a few mesh buildings, because hey...Mesh is awesome like that. But I come across this problem whenever I'm trying to upload this one building.  Just a quick bit, I use Google Sketchup instead of Blender. I find it easier to use.

 

Now, I'm able to upload most meshes from Google Sketchup with no problem, and I'm able to upload this Mesh as well, but the problem comes when I change the physics setting to anything higher than "Lowest".  I'm thinking it has something to do with these Red Dots & Lines which appear on the display window (see Pics).

Generally this isn't too much of a problem for other meshes (Swords, Daggers, Guns, Etc) because their Bounding Box isn't that important... but this a building.  I wanted to walk into it, but with the physics data set so low ... that pretty much nulls it out to where I can't even walk into it anymore (Yes I tried to change the Physics tab from Convex Hull to Prim)

-

I read somewhere that "Wrap" under the physics button was used for things like buildings, to be completely honest with all that... I've no idea what to do to mess with them.  Doesn't help that when I press "Wrap" or anything other than "Surface" the Window doesn't respond anymore.  

 

So....any ideas all you peoples out there? Trying to make a simple building, to where I can walk into it... but it gives me some error.  

Like I said... I think these Red Dots and Lines have something to do with it, but I've no idea why they're there, or what they symbolize.  

(Lowest Setting = Working)

 

(Anything Higher than Lowest = Not Working)

[Monti Messmer]

Hi, i´m linking myself to your thread because with searching it´s the only i found - lol

Same problem here and when i try to upload a smaller shape just for the bounding box the Viewer crashes , even the error uploader crashes ...

Anyone have a tutorial for buildings and their physics, a bit more than the rubberduck things from lindens please

Thanks Monti

[Medhue Simoni]

I really don't have a clue about the red lines. Hopefully, some1 with more knowledge can comment on this. I will say tho, that for something like a building, the lowest LOD means absolutely nothing. No1 will ever see it and you will only be driving your prim count up by trying to make a lowest LOD that is recognizable. This is probably also true with the low LOD also.

What, I think, you need to do for a building, is create the finished building, and a simplified physics for it. You really don't need to make a medium LOD, or the low or lowest. The medium, you can generate with the uploader and get something decent. The physics is the most important tho, and you need to make this yourself. The generator will not produce a good physics box for your building.

You also must set the physics on the object mesh to Prim, to be able to walk around in it. The default physics is always set to convex. Convex means that the physics consists of a structure that surrounds the object, which is the simpliest physic box. Setting the physics to Prim will make it so that the system recognizes the exact physics shape you uploaded with it.

[Maeve Balfour]

Although I don't have the issues you describe here, I have a method which might be useful as a workaround.

Basically, I get annoyed when my customised physics meshes don't properly match my mesh floors (which sometimes results in my AV "walking on air" due to the floor plane sitting higher than the mesh floor). In my modeler AND in the uploader window, my pre-made physics mesh perfectly aligns the main mesh, but for some reason when rezzed the floors are out of alignment - despite my efforts of perfectly matching bounding boxes etc. (Generally this happens if I have a mesh room interior, with most of the physics happening INSIDE the mesh - meshes with exterior based physics are generally fine).  Aargh! LOL.

:matte-motes-big-grin-squint:

Anyways, my workaround is to upload my simplified physics mesh as a mesh in its own right, and the original main mesh I rez as a phantom. I align the two, then apply a full alpha texture to the fake physics mesh. Not ideal, but it works well enough as a functional build. Because the fake physics mesh should already be optimised (low triangle count), there won't be any need to touch the other buttons in the Physics section of the uploader.

If you intend on using this method, I would suggest for the main mesh that you create a basic three-vertex triangle mesh, which you nominate as the physics hull in your main mesh (the one which will be phantom) - it will save on PE, and most likely negate the extra PE cost of the fake physics mesh when the two are combined.

For the fake physics mesh, in the uploader, use it as is for the physics hull (since it should be optimised for physics already). For the LODs section, use the three-vertex triangle for LODs 2, 3 and 4 - it's LODs won't matter, since it will be invisible in usage. Using the triangle for the lower LODs will usually result in a major reduction in its PE cost overall.

So yah, my method is a (not ideal) workaround that I use sometimes, and might be useful to get around the problem you describe.

:matte-motes-smile:

[Drongle McMahon]

Medhue is right. You need to make a special mesh for the physics shape. This should be as simple as possible to obtaing the collision behaviour you need. For example, the roof can be a single flat plane, as can each wall without a door. You only need the pyramidal roof surface if you want to be able to stand on it.

When you have that shape, it shouls have only large triangles and might be cheapes (in physics weight) as a triangle-based shape (no Analyze click!). Or it might be better decomposed into hulls (Analyze). The decomposition tends to work better if the simple boxes making up the shape are not intersecting. For the triangle-based shape, you may find single planes for each wall will work, and they don't need to be separate.

The best way to learn this is to start making physics shapes and first see what the physics weights are by clicking the calculate button. You should aim for a physics weight well below the download weight. Then upload a few on the Aditi grid, where money is free, to see how they work. Both triangle-based and decomposed shapes have to be set to physics shape type Prim.

I think the red markings are triangles which are too small to be acceptable to the physics engine. The engine hates small triangles, which is why the triangle-based physics weights increase as a mesh is made smaller. The convex hull based shapes, either the default hull for the whole mesh or the decomposed shapes, do not change with size.

Now - all that was really written from the point of view of a Blender user, where the whole house would usually be one mesh. However, Sketchup tends to make things as collections of small meshes, which changes things a bit. Each mesh has to have a corresponding physics shape, which may prevent effective simplifications. On the other hand, if each wall is a separate mesh, then the default convex hulls would still allow you to walk inside. It's difficult to say more without detailed specific knowlege about this model.

Finally, you can always consider the option of making the physics model from linked normal box prims with the default transparent texture. Use one of these as root and set the physics shape type of the meshes to None, of the boxes to Prim. Provided you use no (or very few) distortions of simple boxes, they will contribute 0.5 prims each to the download weight (unless you add a script, in which case it will be 1.0 each). This is generally not the best solution for Blender-type buildings, but might be useful here.

ETA ... and Maeve's method too ....

[arton Rotaru]

I wouldn't say the lowest LoD means nothing on a building like that. Depending on the models bounding box radius, it might be meaning nothing regarding land impact. It might not make it into the calculation. In case your bounding box radius is bigger than 10.86 meters, only the High and the Meduim LoD will be considered by the land impact calculation. So you can load the Medium LoD in the Low, and Lowest LoD slot, too. The land impact will be the same as you would set a single triangle for the Lowest and Low LoD.

Though, If my building is this big, that only the Hi and Medium LoD will be considered, I tend to skip even the Meduim LoD, and load the Hi LoD in all slots. This results in a higher land impact for sure, but I don't like main walls of a house structure LoD down in medium LoD already.

The red lines indicate degenerated triangles AFAIK. like Drongle mentioned, those are triangles which are to narrow for the physics engine.

[Nacy Nightfire]

Its helpful to keep the upload screen open with the physics shape showing the red lines while you go back and forth from SL to your 3d package finding those thin thin triangles.  I just made my first house I could actually walk into tonight starting with Sketchup.  I thought previously that it was sufficient to just go into Blender to remove doubles and fix normals,  but I realize now Sketchup makes ALOT of these thin triangles.  I can't think of a way in Blender to uncover them since they are as thin as edges and sit in the same space as other edges.  Referring back to the uploader screen where the red indicators point them out seems like the solution.  Any other tips to uncover them would be appreciated.

I'll also repeat what someone already posted (sorry I forget who pointed this out on the forum) that in the upload screen you can manipulate the image just like any other item in SL..zoom, rotate, etc.  So you can really get in there and find those spots that are giving you grief.

[arton Rotaru]

Well, If I remeber right, on SLCC Runitai said that Sketchup is not an App which works well with the SL importer. And looking at the repeating problems people are havlng with it, I wouldn't recommend to use sketchup for SL at all. (Before people start complaining now, "I have no problems with sketchup and SL", that's fine, go on, use it).

Though, if you are familar with Blender already, like you Nacy, I would recommend to skip Sketchup and model in Blender.

Edit: I should go to bed. Can hardly read my own sentence. :matte-motes-impatient:

[Nacy Nightfire]

I can't completely disagree with you arton, but I've discovered that Sketchup, despite its many limitations for importing mesh objects into SL, is a lot of fun use.  The simple tools and the bright interface is a pleasure and a great way to sketch up floor plans and play around with design ideas. I wouldn't count it out as a useful tool for SL builders, its just not really one that stands by itself.  It's more suitable as a substitute for paper and pen when coming up with plans then for actual modeling.  

So far everything I've made in SU took 3x as much time in Blender getting it fixed up and prepared to upload into SL.  I do suspect that with understanding the program a bit more there may be some hidden tricks to avoid that problematic geometry.

I'm going to bed as well,  happy that I finally understand what those dang red lines mean in the uploader.  Yaaaay!

 

[Nacy Nightfire]

User's of Sketchup have come up with various "clean up" scripts primarily for CAD use,.  One or more of these might, in fact, be the solution.  I'll give this a shot and report back.  (I apologize if I'm deraililng the op's thread here a bit.)

[Sokoda Soulstar]

First of all, thanks to everyone who replied.  And no worries if the topic slightly changes because any help to this is really, greatly appreciated, and more than welcomed.

As for what Medhue Simoni Said, and a few others (sorry for the lack of names I don't know how to view the whole thread to write everyone down when making my own reply) anyway... there's a portion that said I need to make the physics myself? Acutally more than just a portion, nearly all of you have mentioned a custom physics or something similar. I'm confused on this....... how do you make your own physics for a mesh? I thought the uploaded did this by itself.  >.< 

 

Sorry for sounding like an idiot, I just want to start helping out everything and the Forums seems like the best place to go for that.  

 

Also the red lines mean triangles? So then I guess on the export option I don't include Triangles? 

 

Thanks again, really.

[Drongle McMahon]

"how do you make your own physics for a mesh..?"

The same way you make the other mesh(es). The difference is that it is simpler. It is used by the server to work out collisions with other objects and avatars. It is never seen. So it only needs to have the right parts there, without all the details. When it's ready, you upload it by switching to the Physics tab, choosing "Load from File, and the selecting it from the Browse button. You can also tell it to use one of the LOD meshes, but this is not usually as good as a mesh designed for physics, as it generally has too much detail or the wrong shape. . If you don't specify the physics shape either way, then the only physics shape available will be the default convex hull, which means you can't go inside it.

"Also the red lines mean triangles? So then I guess on the export option I don't include Triangles?"

No. The whole mesh is triangles. If it's polygons in the collada file, they are converted into triangles for upload. The red ones are just very small ones, sometimes including ones where the three points lie (nearly) on a line so that the triangle has zero area.

[arton Rotaru]

The importer converts everything into triangles anyway. So you can't avoid triangles.

Here's a picture of the main walls of a house and the physics mesh. As you can see, the physics mesh is just a simplified version of the original mesh.

[Nacy Nightfire]

Ok, I messed around a bit today with some clean up plug-ins for Sketch Up and they did absolutely no good.  I've also have some luck in Sketchup with small things like windows, but I guess the "boolean" style geometry is just too messy on larger things like buildings to be worth the work of cleaning up.  This just wasn't all that obvious to me at first - what takes a short time to build in Sketchup talks a loooong time to fix in Blender.   I agree that it's not worth it, although, again,  fun for small things and for sketching out designs.

[Sokoda Soulstar]

Oh... I feel like an idiot now.  

Okay, thanks.  So the physics of the mesh is just the simple version of the mesh.  Arton, the pictures were a huge help thanks I'm a total visual learner so that helped a great deal, many thanks.  Drongle, thanks also for basically giving me a tutorial lol.  Go to the physics tab and load from file, then grab the physic's mesh I made... that makes so much sense I feel stupid for not thinking of it before.. but thank you .  It's kind of like when you make a sculpty and you have to put invis. prims down so you can walk on it.  

 

And Nacy, thanks for trying I might convert back to using Blender or more often than not, I'll end up juggling both Blender and Sketchup to try to perfect my designs. 

 

Thanks Everyone who helped,

[Da5id Weatherwax]

Yep, the red stuff is where the physics engine sees what it considers degenerate tris. You can get this by simply making a wall too thin or stuff like that.. You dont get a visible error message apart from "errors on upload" but if you look at the log file you see lots of degenerate tris reported. Since the collision shape is not part of the rendered world, if you discover this issue on a structure you can, without harm to the hours of work you may have already put in on the thing, just make the physics walls fatter by making them extend a little beyond the visible inner surface of the wall (dont touch the outside because your physics shape has to have the same bounding box as the visible part). Nobody is going to notice, when moving around inworld, that they actually collide with a wall a little before they truly appear to. You've got a LOT more leeway in that regard than you might think. The physics wall can be significantly thicker than the rendered wall without breaking the experience.

[Luc Starsider]

A quick question to try to understand this better.

Perhaps I'm wrong about this, but physics meshes are double sided, right?

So, in the case of a building like this, where the walls are relatively thin, would it not be sufficient to make the physics mesh using one 'layer' (for lack of a better term) of mesh in the middle of the walls, and not one layer inside and one outside of the walls? This would reduce some of the cost for the build?

- Luc -

[Drongle McMahon]

Yes. I usually use one plane for walls. It works most of the time, but I have very occasionally slipped through for some strange reason. I don't know if that is related to the user of single planes. Of course you will be able to get parts of you buried in the wall too. So if it doesn't change the PE/LI by exceeding the download cost, there's no reason not to use two planes to get a more accurate shape (as far as PE is concerned - I guess the physics engine might not agree).

[Medhue Simoni]

Just some notes that might be relevant. I created a shack where things are rezzed inside and become physical to rest on the floor. I basically had to get rid of the object rezzed being physical and resting on the floor, because that object regularly found spots to fall thru the floor, even tho the floor is 1 solid physical object. The rezzed object is now just rezzed without going physical. I don't really remember if the floor is a single plane or a box.

Also, remember that, although it is great to get a low physics cost, it does not mean much if your model is driving the cost up. With a building, you are not likely to resize it after it is done, so having a super low physics cost that is massively lower than the cost of your model, is not saving you anything. So, you might be getting rid of physics and making your model less desirable, without getting anything for that cut back.

[arton Rotaru]

---

Luc Starsider wrote:

A quick question to try to understand this better.

Perhaps I'm wrong about this, but physics meshes are double sided, right?

So, in the case of a building like this, where the walls are relatively thin, would it not be sufficient to make the physics mesh using one 'layer' (for lack of a better term) of mesh in the middle of the walls, and not one layer inside and one outside of the walls? This would reduce some of the cost for the build?

- Luc -

---

First of all, the walls are not so thin than they might look on the picture. And like Drongle, I had cases where I could walk through the wall in some spots, if I make it one sided. However, I like accuracy for physics, too. Due to the size of this particular mesh (it's Hi LOD only), it has a download weight of 12. The physics weight with a decomposed physics mesh is 4.9. Uploading it as a triangle-based physics mesh, it has a physics weight of 0.5.

While I am all for efficiency, I don't go mad about it. What's worth the best efficiency,  when the build is poor looking, or behave poor physics wise?