

   HALOSIM accurately traces rays and simulates halos.
   
   In contrast, the coloured sky backgrounds that can 
   be selected for the simulations are intended only to be
   pleasing and they make no claim to accuracy.

   SKY TUNER

   This control panel allows the sky colour and horizon 
   shading to be selected.  The results only show when a
   simulation is run with the plot option of 'Grey shades 
   on color' 

   ADJUSTING THE SKY COLOUR

   Display the Sky Tuner by clicking 'Sky Tuner' on the
   Appearance menu.

   Click the 'Color' button to display a standard Windows
   colour selection dialogue box.

   Select/choose the colour and click OK.  Note that the 
   selection can also be stored as a custom color and 
   some custom sky colors have already been prepared.


   SHADED SKIES

   Further controls allow the skies in camera views,zenith
   and nadir centered fisheye views to be shaded so that 
   the sky towards the horizon becomes increasingly white.

   Three options:

       NONE - There is no sky tonal variation
       PRESET - The shading settings are preset
       CUSTOM - User selectable Horizon Brightness
                       and Fill Gradient

       HORIZON BRIGHTNESS
       Move the slider to the right to increase the
       horizon brightness

       FILL GRADIENT
       Move the slider to right to increase the gradient 
       of the sky tonal variation.  A setting leftwards 
       gives a diffuse and gentle sky.

 
   All settings take effect on the next simulation.  
   They are stored with the simulation parameters.



