Techniques for Visualizing the Appearance of Forest Operations

Robert J. McGaughey, USDA Forest Service, Pacific Northwest Research Station (email
This information is designed to augment the article with the same title which appeared in the Journal of Forestry, June 1998. 



geometric model: stand scale 

Geometric model:
stand scale
geometric model: landscape scale 
Geometric model:
landscape scale
video imaging: original image
Video imaging:
original image
video imaging: after modification
Video imaging:
after modification
to add harvest unit
geometric video imaging: wireframe model
Geometric video
imaging: wireframe
geometric video imaging: original photograph
Geometric video
imaging: original
geometric video imaging: retouched image
Geometric video
imaging: retouched
orthophoto draped over digital terrain model
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.

Links to Visualization Related Software

Software package Visualization technique Project scale Computer platform Cost* Contact information
Stand visualization system (SVS) Geometric modeling Plot PC-DOS Free
UTOOLS and UVIEW Geometric modeling Stand or landscape PC-DOS Free
SmartForest Geometric modeling Stand or landscape UNIX (SGI or IBM-RS6000 with OpenGL), Windows 95 (with OpenGL), Windows NT Free
Landscape management system (LMS)** Geometric modeling All scales PC-Windows Free
Adobe Photoshop Video imaging All scales  PC-Windows, macintosh, UNIX $$
Gnu Image Manipulation Program (GIMP) Video imaging All scales  UNIX Free
Paint Shop Pro Video imaging All scales  PC-Windows Free, $$
USFS, Southern Research Station visualization system Geometric modeling Stand or landscape UNIX Free
VistaPro3 Geometric modeling and image draping Landscape PC-DOS, PC-Windows, macintosh $$
IDRISI Image draping and perspective views Landscape PC-DOS, PC-Windows $$
Persistence of vision raytracer (POV-Ray)**** Geometric modeling All scales Many platforms Free
VisualFX Geometric modeling Stand or landscape PC-DOS $$ Available from developer: John Heasley (970) 223-3149
CLRview Geometric modeling Stand or landscape Silicon Graphics IRIX Free
Visual Explorer Image draping and geometric modeling Landscape PC-Windows Free, $$
TruFlite Image draping Landscape PC-Windows Free, $$
World Construction Set Geometric modeling All scales PC-Windows, Amiga, DEC ALPHA with Windows NT $$
*System cost refers to the purchase price of the software.  Free packages are either public domain or otherwise freely available.  Software marked with "$$" are commercial products available at retail outlets or from the software producer.  Items marked with both “free” and $$ indicate that the product is available as a free trial version as well as a commercial version.
**LMS uses SVS to provide plot-scale visualizations and UTOOLS/UVIEW to provide stand- and landscape-scale visualizations.
***VistaPro does not provide for individual tree placement or specification of individual tree characteristics making it difficult to use to accurately representing a variety of stand conditions.
****POV-Ray is a general purpose ray-tracing system capable of producing detailed, realistic images of geometric models.

Related Links

USDA Forest Service
USDA Forest Service
Cooperative for Forest-Systems Engineering
Society of American Foresters
Pacific Northwest Research Station

This page includes references to commercial and non-commercial software products.  Such references are for viewer information and do not imply endorsement by the U.S. Department of Agriculture of any product or service.

Questions or comments regarding this page should be directed to Robert J. McGaughey (email)