boundaries

At the risk of appearing sarcastic ( Me?? I know, right!? ) I would like to let you know that this is not the age of the telegram. You're not charged by the word, so feel free to actually let rip with as much information as possible, because this is another question whose answer depends on information you haven't provided.

However, assuming that you want to limit your camera based on a simple cube zone ( which I'm assuming from your stretched cube comment ) then you can simply check the position boundary against your ( now imaginary ) cube boundaries.

EG:

If CameraPosX>100
   CameraPosX=100
End If
If CameraPosX<-100
   CameraPosX=-100
End If
If CameraPosY>10
   CameraPosY=10
End If
If CameraPosY<0
   CameraPosY=0
End If
If CameraPosZ>100
   CameraPosZ=100
End If
If CameraPosZ<-100
   CameraPosZ=-100
End If

Would limit you to a 200x200x10 zone around the origin.