Precision of object alignment?

[Furholio]

Hello,

assume the following simple scenario: (in Blender) we create a simple plane, cut it in 2 pieces and make each part an separate object. These 2 pieces have no gap in Blender since they are perfectly aligned. When we now select these 2 objects, export them and upload into SL, then I can see a small gap when I'm close with the camera. 

Is this normal? I thought I tried this some time ago and it worked perfectly in SL (no gaps). 

(I'm running into this since I wanted to to cut a larger object into smaller ones for LI optimization ...)

What is your experience with this?

 

Many thanks in advance.

[Wulfie Reanimator]

The further you are from <0,0,0> (ground-level corner of the sim) and if your object's vertices aren't at exact units, the more likely you are to see gaps. This is caused by rounding errors in the rendering process and has always been the case, long before mesh existed.

[Furholio]

7 hours ago, Wulfie Reanimator said:

The further you are from <0,0,0> (ground-level corner of the sim) and if your object's vertices aren't at exact units, the more likely you are to see gaps. This is caused by rounding errors in the rendering process and has always been the case, long before mesh existed.

Thanks for that hint. I wonder how to get the verts to exact units. I assume whats important is the bounding-box center as reference, and from there I need to snap the verts into exacts units? Can I assume metric unit for SL? 

I'll just play around some ... 

[Profaitchikenz Haiku]

Bear in mind also that the minimum dimension of an object on any axis is 0.01m, so if you have two pieces supposedly abutting but one is 3.124m width and the other 3.876m width you will not get them to align, no matter what altitude you position the build at.

[Furholio]

1 hour ago, Profaitchikenz Haiku said:

Bear in mind also that the minimum dimension of an object on any axis is 0.01m, so if you have two pieces supposedly abutting but one is 3.124m width and the other 3.876m width you will not get them to align, no matter what altitude you position the build at.

Hello Haiku,

I don't really understand. I don't see a relation between the min. size of an object and the precision of vertex positions ...

 

[Quarrel Kukulcan]

3 hours ago, Furholio said:

I don't really understand. I don't see a relation between the min. size of an object and the precision of vertex positions

If SL has to enlarge your object so no single dimension is less than 1 cm long, it'll magnify any misalignment between parts.

[Wulfie Reanimator]

5 hours ago, Furholio said:

Thanks for that hint. I wonder how to get the verts to exact units. I assume whats important is the bounding-box center as reference, and from there I need to snap the verts into exacts units? Can I assume metric unit for SL? 

I'll just play around some ... 

What I meant by "exact units" was basically "integer offsets" but on second thought I'm not too sure on the exact details (like the fact that objects are scaled to unit-size volume, etc), so I would disregard that thought.

Anyway, yes, the SL world is metric. Can you show an example of the actual model you're trying to make work, and where (what height) the gaps appear?

 

43 minutes ago, Quarrel Kukulcan said:

If SL has to enlarge your object so no single dimension is less than 1 cm long, it'll magnify any misalignment between parts.

This is not the connection made by Profait. It's true that trying to align 3.124m with 3.876m is going to be basically impossible (by hand), but that has nothing to do with the minimum object size of 0.1m. You can certainly have verts closer together than that.

 

I made this real quick:

The two planes are separate meshes, with one edge positioned exactly on top of each other. In SL it looks totally fine at 4000 altitude. (The seam is on the left side in the below picture, the camera is extremely close to where the gap would appear. No gap is visible regardless of camera angle.

Edited September 28, 2020 by Wulfie Reanimator

[Furholio]

18 hours ago, Wulfie Reanimator said:

What I meant by "exact units" was basically "integer offsets" but on second thought I'm not too sure on the exact details (like the fact that objects are scaled to unit-size volume, etc), so I would disregard that thought.

Anyway, yes, the SL world is metric. Can you show an example of the actual model you're trying to make work, and where (what height) the gaps appear?

 

This is not the connection made by Profait. It's true that trying to align 3.124m with 3.876m is going to be basically impossible (by hand), but that has nothing to do with the minimum object size of 0.1m. You can certainly have verts closer together than that.

 

I made this real quick:

 

The two planes are separate meshes, with one edge positioned exactly on top of each other. In SL it looks totally fine at 4000 altitude. (The seam is on the left side in the below picture, the camera is extremely close to where the gap would appear. No gap is visible regardless of camera angle.

 

Hello Wolfie,

thanks for the effort. I meanwhile remodeled to avoid the problem. But before I had it the same as you did. I reduced everything to 2 simple faces which were the 2 objects. I even looked into the .dae file to check the positions, and the regarding vertices had exactly the same positions down to the very last digit. But still I was able to see the gap in SL. I tried at different locations on the sim but it didn't make any difference. I tried more stuff like applying all object transforms in Blender and not using the scaling option in the uploader (which I did before) but nothing helped.