Reflectance Map Options

Set these options:

  These parameters define the reflectance map:
  • Sun azimuth: compass direction to the sun. By convention this will be to the northwest (upper left), which is where our mind is used to seeing artistic lighting.  The circle on the upper right lets you move the sun by double clicking. illumination. Although this is impossible for most of the "real world" (North Hemisphere, non-tropics), it avoids the problem of valleys and ridges trading places.
  • Sun elevation: elevation angle for the sun. This changes the illumination and shadows. It is measured from the horizon and ranges from 0 to 90 at the zenith (directly overhead).  The circle on the upper right lets you move the sun by double clicking.  The center of the map is 90 elevation, the edges 0.
  • Vertical exaggeration: for typical DEMs this is not necessary, but in very low relief areas or very small scale DEMs you might want to increase this parameter if the default contrast is too low. For 10-30 m DEMs, set VE to 1-2 for starting, while for Global Data like ETOPO try VE=15.  Two levels of default are now kept, for small and large scale DEMs.
  • Water options:
    • Sea Level check: if selected, water (defined as zero elevation) will be colored distinctively. This cannot be done if elevation tints are selected.
    • Lake check: if selected, water (defined as nine adjacent points with the same elevation) will be colored distinctively. This cannot be done if elevation tints are selected. The lake check may not behave correctly in very flat, stair step DEMs.
  • Diffuse reflectance: diffuse reflectance uses a reflectance algorithm from Pelton (1987). If unchecked, aspect-based shading is used, which uses many fewer parameters.  Buckley and others (2004) suggest that in mountainous terrain diffuse reflectance may give better results.
  • Z range: lets you select the elevation range used for the elevation colors if they are not simply grayscale.
  • Saturation--use very lightly.  Saturation lets you interactively adjust the IHS view.
  • Directions to average: multidirection options.  They will be equally spaced in azimuth, and all share the same sun elevation.  Only applies with diffuse reflectance
  • Default button will return to the following values:
    • Sun azimuth: 335
    • Sun elevation: 45
    • Vert exag: 1
    • Elevation tints: off
    • Sea level check: on
    • Lake check: off
    • Underwater elevs: off
    • Colors: IHS elevation
    • Diffuse reflectance
    • Directions to average: 1
Elevation colors in hillshade:
  • Grays: no elevation colors, just terrain shading.  This may be best when overlaying colored vector data.
  • Blue/Green: blue below sea level, and green above.
  • Six colors:  color will correspond to elevation, with six categories (blue, cyan, green, yellow, red, magenta), and the intensity of the color will correspond with the amount of light reflected. 
  • IHS elev merge: shadows and elevation colors; this is the default
  • Gray/color: land in gray, oceans in color
  • Gray/blue: land in gray, water in blue

 

Reflectance map theory.

Multi direction hillshades

Reflectance map references.


Last revision 9/17/2018