WELCOME TO THE THUNDERSTORM DEMO

   This application demonstrates the advanced
   visualization and data exploration capabilities of
   IDL's OpenGL-based Object Graphics System.  The
   data consists of temperature, pressure, and wind
   velocity samples for a simulated storm front model
   in three (x, y, z) spatial dimensions.  This is
   analogous to measuring three parameters (pressure,
   temperature and wind velocity) in evenly spaced (x,
   y, z) locations of a room.  Each measured parameter
   consists of a "brick" or volume of data, thus we
   have three "bricks" of data to display.

   In addition to these advanced visualization
   capabilities, the array-based nature of IDL
   facilitates the analysis of complex,
   multidimensional data. If desired, all dimensions
   of complex data may be stored and processed in a
   single array.

   Our most sincere thanks go to Drs. Joe Klemp and
   Morris Weisman of the National Center for Atmospheric
   Research (NCAR) Boulder, Colorado who graciously
   provided Research Systems with this data.

   The following types of visualizations can be shown.

   Images obtained from cross-sections of the data.
   Vector plots of velocity at a given location.
   Volume rendering of a variable throughout the data set.
   Isosurfacing of a variable.
   Ribbons for the display of vector data.

   The data available for use in the demo:

   P: air pressure pertubation (millibars)
   T: potential temperature pertubation (difference
   from mean in degrees Kelvin
   U: wind field west to east (meters/second)
   V: wind field south to north (m/sec)
   W: wind field vertical velocity (m/sec)
   (Note that the variable M shown in the visualization
   is a computed value based on U, V, and W)

   MENU OPTIONS
   ------------
   File Menu:
      Select Quit to exit the Demo and return 
      to the IDL Demo system.

   About Menu:
      Select "About Thunderstorm Visualization" for detailed
      information about the Thunderstorm Demo.


   FEATURES
   --------

   <<Velocity Field Planes: X, Y, Z>> droplists
      
      Control the display of velocity information for each plane.
      The display of velocities can be shown as vectors, as an
      image, or turned off.

   <<Velocity Field Planes: X, Y, Z, Plane>> sliders
      
      Control the location of the plane in which velocity
      information is to be displayed.

   <<Vector Sampling>> button group
      
      Choose "Even" or "Random" sampling for the display of
      velocity vectors.

   <<Sample Every Nth>> text entry field
      
      Set the density of the sampling for the display of
      velocity vectors.

   <<Total Number of Samples>> text entry field
      
      Set the total number of velocity vectors to be displayed
      when using random vector sampling.

   <<Vector Length>> text entry field
      
      Set the length of the velocity vectors.

   <<Vrend vol>> droplist
      
      Choose the volume to be rendered.  "P" represents air
      pressure perturbation in millibars.  "T" represents
      potential temperature perturbation, or the difference
      from mean in degrees Kelvin.  "M" represents the magnitude
      of the wind velocity.

   <<Vol Render>> button
      
      Display the volume rendering selected with the "Vrend vol"
      droplist.

   <<Img vol>> droplist
      
      Select "P", "T", or "M" to display air pressure, temperature,
      or the magnitude of wind velocity when the Field Planes droplists
      are set to "Image".

   <<Iso vol>> droplist
      
      Select the data set to be displayed as an isosurface, using the
      same settings as in the "Img vol" droplist.

   <<Level>> slider
      
      Set the data value to be used for the isosurface.

   <<IsoShow>> check box
      
      Check this box to display the isosurface.

   <<Transparency Min.>> slider
      
      Adjust the minimum value used for transparency in
      the display of the field planes when the field plane
      display is set to "Image".

   <<Transparency Max.>> slider
      
      Adjust the maximum value used for transparency in
      the display of the field planes when the field plane
      display is set to "Image".

   <<Clear Streamlines>> button
      
      Remove the display of streamlines.  Streamlines are
      created by clicking the right mouse button (or emulated
      right mouse button) on a field plane image or isosurface.