Visualization
examples
Geometric model:
stand scale
Geometric model:
landscape scale
Video imaging:
original image
Video imaging:
after modification
to add harvest unit
Geometric video
imaging: wireframe
model
Geometric video
imaging: original
photograph
Geometric video
imaging: retouched
image
Orthophoto draped
over a digital
terrain model
|
The appearance of landscapes and individual stands after harvest
operations is critical to public acceptance of timber harvest practices.
Thorough planning, detailed site-specific analysis, and careful monitoring
of harvest activities will not result in truly successful operations if
the public views the resulting landscape as an eyesore. Activities intended
to mitigate the visual impact of harvests include modifying unit boundaries
to conform to topography and other natural stand openings, prescribing
silvicultural treatments that retain higher numbers of standing trees or
groups of trees, and attempting to "hide" or "screen" harvest units from
sight. These mitigation efforts can be successful. However, foresters charged
with designing harvest unit shapes and silvicultural treatments often find
it difficult to develop visually acceptable solutions by working in the
field or with planimetric maps and aerial photographs. Visualizations depicting
the appearance of a treatment or harvest operation provide important feedback
during the design process and help to communicate management intentions
to resource specialists and public stakeholders.
Forestry professionals have used visualization techniques to address
a variety of forest management problems. Prior to the advent of computerized
methods, they used "artists' renditions" to communicate the effects of
land management activities. Perspective sketches and scale models continue
to help communicate the spatial arrangement and extent of management activities
to the lay public. However, current practices in forest management involve
more detailed harvest designs involving small treatment areas scattered
over larger landscapes and the removal or modification of specific stand
components. Alternative treatments utilize different mechanical methods,
vary the spatial arrangement of treatment units, and specify different
levels of modification within individual treatment units. With such treatments,
the traditional "artists' rendition" cannot be made specific enough to
represent the subtle differences between alternative treatments.
Computerized visualization methods range from simple diagrams to complete
virtual realities. Four methods are commonly used to produce visual representations
of forest operations: geometric modeling, video imaging, geometric video
imaging, and image draping.
Geometric Modeling
Geometric modeling methods build geometric models of individual components
(ground surface, trees, other plants, and structures) and then assemble
the component models to create an image of a forest stand or landscape.
Scenes depicting the complete model are then rendered from a variety of
viewpoints. In its simplest form, this technique can be used to generate
perspective drawings showing typical GIS data coverages such as roads,
streams, and polygon data overlaid onto the ground surface. More complex
applications build detailed models of individual trees that include small
branches and leaves for use in rendering.
Video Imaging
Video imaging uses computer programs to modify scanned full-color video
or photographic images to represent changes to stand and landscape conditions.
Video imaging produces television-quality (or better), full-color visual
representations that depict current and future conditions. Video imaging
typically requires a library of images representing different forest conditions
to replace portions of an original image, however, direct manipulation
of images is also possible.
Geometric Video Imaging
A hybrid approach, termed geometric video imaging for this discussion,
combines geometric modeling and video imaging techniques to produce very
realistic images that accurately represent data describing the effects
of forest management activities. Operators use geometric modeling to produce
scenes that specify the location, arrangement, and scale of proposed landscape
changes. Video imaging is then used to modify a digitized image to reflect
these changes. The technique can be extended to use geometric modeling
to determine the locations for digitized images, or icons, of single trees.
Hybrid approaches result in images that accurately reflect the data describing
proposed changes. However, to produce photo-like images, hybrid techniques
require extensive libraries of tree and stand images that represent an
appropriate range of species, tree sizes, growth forms, and landscape positions.
Image Draping
Image draping mathematically "drapes" an image over a digital terrain model
and then renders the resulting scene from a variety of viewpoints. Operators
usually obtain the image from a satellite scene, aerial photograph, orthophoto,
or map sheet and use techniques common to video imaging to modify the original
image to reflect management activities. Several GIS and image processing
applications provide draping capabilities. Most include rectification procedures
to properly orient and align a digital image to the ground surface. Simple
applications utilize orthophoto images that have already been registered
to the ground surface and corrected for elevation, or relief, displacement. |
