Reflectance Map/ Hillshade 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.
  • Sea level: used to shade above or below a particular level
  • Top: used for a two or three color scheme for change maps
  • Base: used for a two or three color scheme for change maps
  • 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 factory settings
Elevation colors in hillshade:
  • Grays: no elevation colors, just terrain shading.  This may be best when overlaying colored vector data.
  • IHS elev merge: shadows and elevation colors; this is the default
  • 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.
  • Blue/Green: blue below sea level, and green above.  Uses the sea level value for a different base line.
  • Gray/color: land in gray, oceans in color. Uses the sea level value for a different base line.
  • Gray/blue: land in gray, water in blue.  Uses the sea level value for a different base line.

 

Color Options for change maps
  • Green/Yellow/Red.  Green above the top level, yellow in the middle. and red below the base level.  If top and bottom are the same, the map will be just green and red.
  • Green/Gray/Red.  Green above the top, gray in the middle. and red below the base.

Start with top and base that you think will define the level at which  change will be important.  Zero is no change, but values close to zero could be random noise.  For two colors, make the base and top the same.  For three colors, the middle category, either gray or yellow, is not important and you can focus on just the important changes.

This color scheme will not show the magnitude of changes, but helps you focus your analysis.

Reflectance map theory

Multi direction hillshades

Reflectance map references


Last revision 1/17/2022