Line Coordinates

Hi Bill and others, I am trying to create 3D line shapes (for oil well paths) 
in the context of elevation surfaces (flatfields of func types of
(x, y) --> (z, etc), as mentioned in my previous e-mails and sample program).  
I notice that for VisAD line shapes:

"...Spatial coordinates vary from -1.0f to +1.0f in the VisAD display "box". In 
general, the coordinates of shapes should be centered around the
origin (0.0f, 0.0f, 0.0f) and scaled appropriately relative to the "box" 
dimensions. Use RealTypes mapped to spatial DisplayRealTypes to
determine absolute shape locations, and RealTypes mapped to ShapeScale to 
determine relative shape sizes."

I need to specify the line points in real world coordinates (x, y, z).  How can 
I do that in the context explained above?   Thanks.

-- mohamad