How do I drop an Obj on the terrain,sometime I it seem like the obj is on the ground but it's actually floating in the air.

I used to love Poser's "drop to ground" command, but haven't found anything like it in Carrara. I manually drag the objects into place.
One trick is to move the hot point to the bottom of the object, then tell the hot point to go to z=0.

what do you mean by the hot point.

 You cna try the collision detection tool, but for high density mesh like Vic you will need a little patiente. But in general people use the all viewes to be right about the place where chars are in the scene.

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Every object has a center and a hot point, often they are in the same location. You can find them in the properties pallete, under the MOTION tab. In the "transform" section you will find the x, y, z coordinates of the hotpoint and the center.
If you unclick "lock hotpoint" you can move the hotpoint.

Thanks!!

 sparrowhawke has a great terrain following plugin could help

Attached Link: http://www.sparrowhawke3d.com/Sparrowhawke3DPlugins.html

I was just going to say what the guy above me said.

In addition to the terrain follower, I think the transforms package also has a way of dropping things to the ground.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.

Quote -  sparrowhawke has a great terrain following plugin could help

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Hundreds of shaders for Carrara