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   Draw terrain.
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   Form:
   [h, v] = DrawTerrain( type, d, hAxes )
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   ------
   Inputs
   ------
   type        (1,:) Type 'flat' is the only option
   d           (1,1) Dimension data, for 'flat'
                     d.w width of grid
                     d.n number of points
   hAxes       (1,1) Handle to axes

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   Outputs
   -------
   h                 Handle to the patch
   v                 Vertices

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