/[gzz]/gzz/doc/pegboard/1010/PEG_1010.rst
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revision 1.3 by tjl, Sun Oct 6 17:24:00 2002 UTC revision 1.4 by tjl, Sun Oct 6 17:37:46 2002 UTC
# Line 32  Derived coordinate system type Line 32  Derived coordinate system type
32      implemented internally by generating a set of parameters      implemented internally by generating a set of parameters
33      for the parent type.      for the parent type.
34    
35      For example, the buoytrans coordinate system, which is          For example, the buoytrans coordinate system, which is
36      a translation to the location where the buoy should be,          a translation to the location where the buoy should be,
37      based on a          based on a point in an anchor coordinate system.
38                This means that the buoy will move naturally when the
39          (Benja:) Example? Is rotation derived from affine?          anchor point moves, instead of linearly interpolating.
40            However, the buoytrans function will never transform
41            in any way that's not representable as a pure translation.
42    
43  Parent coordinate system  Parent coordinate system
44      A coordinate system through which the coordinates, having      A coordinate system through which the coordinates, having
45      been transformed by the child, are transformed::      been transformed by the child, are transformed::
46    
47          p_screen = parent(child(p))          p_screen = parent(child(p)),
48                    
49      (Benja says:) Where ``p`` is the original point (in child coordsys),      where ``p`` is the original point (in child coordsys),
50      ``child()`` is the transformation of the coordsys itself,      ``child()`` is the transformation of the coordsys itself,
51      ``parent()`` is the transformation of the coordsys' parent,      ``parent()`` is the transformation of the coordsys' parent,
52      and ``p_screen`` is the final point in screen coordinates.      and ``p_screen`` is the final point in screen coordinates.
53            
54      All derived coordinate system types have exactly the same      All derived coordinate system types have exactly the same
55      parent coordinate system(s) and interpretations as the      parent coordinate system(s) and interpretations as the
56      parent coordinate system type.      parent coordinate system transformations.
57        
         (Benja:) I don't understand this. Is 'parent coordinate  
         system type' the type of the parent coordsys or the  
         coordinate system type *this* coordinate system type  
         is derived from?  
           
58      Currently all coordinate systems have only one parent.      Currently all coordinate systems have only one parent.
59    
60      The theoretical point here is that the parent coordinate      The theoretical point here is that the parent coordinate

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