[Opensim-users] Mesh for physics on new opensim versions

[AJLDuarte]

Hi,
	A single mesh asset does contain several meshs internally.
	- Some are for the visual representation of the object, you can have
four corresponding to different levels of detail (LOD), used according to
the view distance. You must provide the one with most detail. You can let
viewer create the others, or provide your own.
	- others are for the physics representation of the object, mainly
for collisions.

Considering physics.
Viewers will always create a very low detail convex (i.e. without holes etc
) hull.
You select a higher resolution mesh for collisions, if you like people to
get inside your houses for example.
You can provide one or select one of the visual LODS.
That mesh can be encoded as normal mesh or as a decomposition of it in
convex hulls. Some viewers don't support this last option for opensim, in
fact some physics engines don't like it much, so use the mesh for now.

In world you can use Physics Shape type for more control.
	- type None, the physics mesh are ignored, the object will not
collide with anything, its like phantom.
	- type Prim, the high resolution physics mesh will be used. If none
was uploaded, this type is not available.
	- type Convex. The default simple convex hull is used.	 
On mesh upload the type is set to convex. You need to change it.
Linkset root (or individual) prims cannot have type none (set them phantom).

Viewers now allow you to not choose any mesh for physics.
In this case the prim will collide only with the simple low resolution
convex hull with the type selected as Convex or will not collide if is a
child prim with type selected as None.

This is the expected behavior, and will be in future opensim versions.
This is the behavior with physics engine ubOde and ubMeshmerizer.

In current versions, using other physics engine and Meshmerizer, if you do
not provide a high resolution mesh for physics, incorrectly the simulator
will use a mesh from the visual part.
Your creation will seem to work, but you will have issues changing the
physics shape type, and the viewers option to display the physics shape will
not work correctly. We can see several meshs like this in world now.

For this reason this use of visual part of the mesh for physics will be
removed in future versions.

Please check if you creations where uploaded correctly.
If you want high resolution collisions, make sure the type PRIM is available
to select in world. (if you only want the simple convex or no collision,
then its ok).

If a new upload is no longer possible, the object can still be fixed,
setting the mesh to type none, and adding to the linkset invisible prims
(simple boxes are the best option) to do the missing collisions.
You can (should?) do this alse in case a object was uploaded with a
excessive large mesh for physics. Specially if using on vehicles..

Regards,
Ubit