Yellowstone Lake, the largest mountain lake in North America, is visible in the center of this east-looking view from a vantage point about seven kilometers above Old Faithful geyser. Framing the horizon are the 3,300-meter peaks of the Absaroka Range and the fog-filled Yellowstone River valley (upper right.) Recent forest fires, driven by southwest winds, have left gray scars on the lodgepole pine forests of the Central Plateau (lower left.)

Color enhancement

The Yellowstone scene was constructed from a natural color Landsat image, draped on a DEM. In its raw form the Landsat image was unsuitable for presentation. Lakes were nearly black, forests were more gray than green, barren ridges were yellow, and dark shadows covered steep slopes. Photoshopís color adjustment tools were used to correct the Landsat image before rendering the final scene in Bryce. Despite adjustments, colors continued to look unnatural in the lower right corner. Fog, created from flattened spheres mapped with transparent white texture, disguised the problem.


Illumination originates from the lower right to match the Landsat imageís southeast light source. Excessive shadowing (shadows from 3D lighting combine with shadows on the Landsat image) was avoided by elevating the light source close to the zenith.


Bump map texture enhances surface detail in the Yellowstone scene. The bump map was created from a grayscale copy of the Landsat image and, in Photoshop, a light amount of uniform noise was added to forested areas. When the bump map image was imported into Bryce as an alpha channel, the noise created the illusion of an irregular forest canopy on the otherwise smooth surface.

This enlargement shows the tree texture created from bump mapped noise. Pixelization dissappears when printed at smaller size.



The horizon is essential for making a panorama look realistic. However, to show the horizon, a panorama must be viewed from a low elevation by an imaginary camera. The low elevation view limits visibility in mountainous areas where foreground topography obscures the background. Raising the viewing elevation solves the problem of obscured topography, but the horizon disappears and realism is diminished.


The panoramas painted by Heinrich Berann combine map-like readability and a realistic horizon by using foreshortening, a traditional art technique. Applied to a panorama, foreshortening gradually flattens the landscape deeper into the scene until the horizon appears. Although geographic reality has been manipulated for graphic effect, the final results look convincingly realistic.

Digital implementation

Foreshortening was introduced to Yellowstone by warping the DEM on a convex arc, bulging the foreground toward the viewer, and flattening the background. Warping was produced by blending the DEM with a linear gradient that changed from black (front) to white (middle) to black (back). It is the gradient that produces a convex arc when extruded in a 3D program. Varying the blending opacity between the DEM and linear gradient controls how convex the DEM will be.

Blending the Yellowstone DEM with a gradient (left) produces a convex DEM (right).

In the final step, the convex DEM was imported into the 3D environment of Bryce. The DEM was positioned vertically with its back edge aligned to the horizon and rotated horizontally so that its front faced the viewer. Once positioned, apparent foreshortening could be  increased or decreased by rotating the DEM on the axis perpendicular to the horizon.


A convex DEM can only be viewed from its front or back, perpendicular to the axis of curvature. Other viewing directions look unrealistic because the curved surface of the DEM does not synchronize with perspective within the scene. Any changes to the viewing direction, however small, require the creation of a new convex DEM.

Blending a DEM with a linear gradient can degrade topographic detail because Photoshop has only 256 grayscale levels available for displaying height data. Typical symptoms of DEM degradation are banding in flat areas and terrain generalization.  Fortunately, draped imagery and procedural textures can be used to disguise poor quality DEMís.

The convex Yellowstone DEM reveals its curvature in side view (left). The landscape shows distance foreshortening when viewed from the front (middle) and looks more natural when draped with imagery (right).