WELCOME TO THE GRID DEMO


   This demo shows the gridding of unevenly spaced data
   and various interpolation methods.

   A random set of data in 3D space is generated. The 
   Delauney triangulation method connects the data, 
   forming triangles. The triangulated data is then
   interpolated to a location in a 3D grid. IDL offers
   several interpolation techniques. 


   MENU OPTIONS
   ------------

   File Menu:
      Select "Quit" to exit the Grid Demo and return 
      to the IDL Demo main screen.

   Data Menu:
       Select "Generate new data" to create a new set 
       of random data points (X, Y, Z).

   Help Menu:
       Select "About interpolation and gridding" for
       information about the Grid Demo.


   DROPLIST FEATURE
   ----------------

   <<X-Y point locations>>
      Shows the X-Y locations of randomly-generated data 
      points in 3D space.

   <<Delauney triangulation>>
      The random data points are connected using the 
      Delauney triangulation method.

   <<Bilinear interpolation>>
      After the triangulation is performed, the data is 
      interpolated linearly, generating a series of flat, 
      interconnected surfaces. Data points located outside 
      the outer edges of the triangulated surface are not 
      interpolated. These points are assigned values 
      of -20.

   <<Quintic interpolation>>
      After the triangulation is performed, the data is 
      interpolated using the quintic method. Data points 
      located outside the outer edges of the triangulated 
      surface are not interpolated. These points are 
      assigned values of -20.

   <<Smooth interpolation>>
      After the triangulation is performed, the data is 
      interpolated using the 'Smooth' method, which 
      computes a boxcar average, given a width. The result
      is a smooth continuous surface, without a skirt. Data 
      outside the triangulated surface can be extrapolated.

   <<Kriging>>
      Also known as 'Optimal interpolation', this method 
      uses an exponential scheme. It is widely accepted by 
      the scientific community. The result is a smooth 
      surface. Data outside the triangulated surface can be 
      extrapolated.