Secondlife servers provide a default Invisible Avatar as inventory item Library->Body Parts->Alpha Masks->Invisible Avatar. On Secondlife it is easy to use this invisible avatar alpha mask with a rigged mesh avatar to make the underlying mesh visible.
OpenSim does not provide this in its OpenSim Library. There are iar files that can be used to import the invisible avatar to an avatar’s inventory however, this requires access to the OpenSim server console. If there are procedures to perform a client import of an iar file someone please comment. Following the procedure below results in an Invisible Avatar Alpha Mask in your inventory.
Adding an alpha layer when none exists in the avatars inventory.
Right click and select Appearance.
Select Edit Outfit.
In the drop down next to Add More… button Select Alpha.
Since there are no alpha layers in inventory Loading… will be present.
Towards the bottom there is a bar with a gear icon. Notice two text lines icons. The one next to the gear is grayed out. This is for a full inventory display and the selected one next to it is for a filtered display of Alpha masks.
Select the grayed out text lines icon. The entire inventory is now present.
Right click on the Body Parts folder.
Arrow down to new clothes and another menu list will be present.
Select New Alpha Mask.
New Alpha object is now present in the Clothing folder.
Right click and wear the New Alpha. The New Alpha has no alpha mask selected so, there is no change to the avatar.
Cursor up to the upper part of the Edit Outfit panel and under the Body Parts folder select the worn New Alpha.
Select the wrench icon and the Editing Alpha Mask panel will activate.
Enable all five default alpha mask with the check marks next to the alpha texture thumbnail graphics.
The avatar is now invisible. Attachments will still be present.
Select Save As. Name it.
Close out the Edit Outfit panel.
The only thing left visible of the avatar should be a name tag and attachments.
Invisible Avatar may be worn to expose rigged mesh avatars and then taken off as desired.
Note: This procedure could be avoided completely if Opensimulator project provided the Invisible Avatar in its OpenSim Library.
Comments to improve this procedure are welcome.