Yesterday’s post dealt with the basics of installing MicroDEM, and opening up DEM terrain files in the program. Now it’s time to look at different ways to display terrain reflectance in DEM. While 3DEM is better for some kinds of displays, MicroDEM has more different ways to display reflectance.
Here’s the last reflectance plot from yesterday:
Right-click on the image in the program, and choose “Reflectance options”:
At the very top, you set the position of the sun, which in turn changes the degree and direction of shading in the terrain image. You can either enter the sun’s azimuth and elevation numerically in the boxes, or double-click in the circle at the upper-right to change the sun’s position as represented by the red dot. A subset preview of the image will appear in the lower right to show you what kind of effect your changes might have. You can modify the degree of vertical exaggeration to accentuate features in the terrain display. For example, setting the exaggeration to 4 changes the image above to the more dramatic one below:
“Underwater elevs” is used only with bathymetric data (topography of the ocean’s bottom). “Diffuse reflectance” is check as the default; uncheck it, and the shading become dependent on the “aspect” of the terrain, the direction a slope is facing. This can be better in mountainous terrain, but can result in DEM artifacts in flatter areas:
For colors, there are four options:
IHS elev (default) – Used in the above examples. Shades the terrain with different colors depending on how high it is. You can use the Saturation slider near the bottom to modify the intensity of the color.
Six colors – Similar to the above, but uses only 6 colors (blue to red) to differentiate different elevations:
Blue/green – Usually only used for terrain along the coast; shades elevations above sea level as green, at or below sea level as blue.
Gray – Shades the entire terrain as gray. My favorite, since it shows the terrain without color distractions. Here’s gray with a 2x vertical exaggeration:
When gray is selected, the “Sea level check” and “Lake check” options will be enabled at left. Checking the sea level box will tint the DEM with a different color at an elevation of 0. If you check the lake box, MicroDEM will examine the terrain looking for 9 points with the exact same elevation, assume they are a water body, and color it as well.
Finally, if you right click on a gray reflectance image, and select 3D Map Options, you can create a 3D red-blue anaglyph and/or separate stereo pairs of the terrain:
The “Max displacement” is the pixel shift between the two images; default is 30, but 15 seems to work better to start off with. Click OK, and in this case we get a red-blue anaglyph (get your 3D glasses out for this one):
Don’t have red-blue 3D glasses? You can get a pair for the price of a self-addressed stamped envelope from this site; you can also order a high-quality pair from that site, or the Berezin 3D site, for less than $10.