Why does the behavior of snap seem "weird"? So, to test volume in luxrender, I am setting up a series of diffraction: I want some water in a glass beaker, or something like that.  Problem: the fluid simulator is incredibly slow (granted, my meshes are kinda high resolution) so I decided to simply go Ah!  I'll just snap some items together - for example, I'll just take a cylinder and snap it to the edges of the beaker on a transform!  

Well, whenever I try to use snap, it looks like this: 


Not, that is not a short beaker; that is my beaker snapped to the plane everything is sitting on right in the middle of the beaker.  I can guess why you might want this behavior, but I can't get the snap tool to do anything useful!

So my question is: how can I get the bottom of the beaker to snap to the plane, the bottom of the cylinder to snap to the bottom of the beaker, and the sides of the cylinder to snap to the sides of the beaker!

Thanks, this has been incredibly aggravating.
(I normally include a link to a blend file, but this is a two minute setup.)
I believe you need to use the 3D Cursor for this.

In few words, you need to position the origin of the object in the right place first, then position the 3D Cursor where you need the object "by it's origin" to snap to.


Select the breaker.
In Edit mode select the bottom faces of the breaker, or a central vertex/edges/faces.
Shift + S > Cursor to Selected, now you have the 3D cursor at the bottom of the breaker in the center.
Go to Object mode.
Ctrl+Shift+Alt+C > Origin to 3D Cursor, now you have the origin of the breaker in the bottom center.
Select the plane, in Object mode, Shift+S > Cursor to Selected, again this will position the 3D cursor in the center of the plane.
Select the breaker, Shift+S > Selection to Cursor, now you moved the object "breaker" with the new origin that you positioned in step "5" to the center of the plane.


Hope this helps.