0723-B1
T. Panagopoulos[1]
Visibility analysis based on view sheds is one of the tools used in geographic information system (GIS) analysis. Scenic landscapes are integral components of any forest resource base; and should be identified and described in any forest development plan. A visual impact assessment is typically prepared when forest development or access management plans are proposing harvesting, soil preparation, reforestation and road construction in scenic areas. The present study presents the assessment of visual impact in the context of a management plan for some of forest development projects in high aesthetic value areas of the "Serra of Monchique", Portugal. GIS-based visualization techniques historically have been used to help communities understand and manage their resources. Understanding of the impacts of planning policy in mountainous areas is often lost in two-dimensional presentation. To facilitate a better understanding, new technologies, similar to those found in flight simulators, were developed to help people visualize change. These simulations were created in Arcview using digital elevation data. The development of a 3D GIS helped in making better and quicker decisions and to avoid visual and other negative impacts of forest development projects on tourist attractions.
Scenic landscapes are integral component of any forest resource base (Hatzistathis and Ispikoudis 1992). Those landscapes are typically identified and described in forest development plans. With the development of more straight practices codes and environmentally based guidelines, land owners, forest planners, designers and managers, will incorporate visual landscape management into their plans as part of sustainable forest management and provide more detailed and comprehensive visual impact assessments with their development plans (Bell 2001). A visual impact assessment (VIA) should be prepared when the forest development and access management plans are proposing harvesting, soil preparation, reforestation and road construction in scenic areas. The visual impact assessment should be made available for public review and demonstrate that the proposed operations will achieve the visual quality objectives (Lucas 1991).The use of geographic information systems based, visualization techniques historically has been used to help communities understand and manage their resources (Eddy and Looney 1993; Crist et al. 2000; Pullar and Tidey 2001; Sung et al. 2001). The development of mountainous areas shuld be environmentally friendly. GIS systems provide a remarkably efficient means of storing and retrieving information on topography, ownership, vegetation, wildlife habitat, geology, slopes, zoning and a host of other attributes that can provide at least a gross understanding of the characteristics of large areas (Campbell and Ogden 1999). GIS technology saw a great proliferation lastly in the urban and regional planning community, assisting in different phases of the visual landscape planning and decision making processes (Leitão 1997). GIS technology was used by land-use planners to assess the criteria requested to define the suitability of preserved landscape (Florent and Musy 2001), to estimate changes in the visibility of land cover (Miller 2001), to assess land-use impacts on biodiversity and conservation planning (Theobald et al. 2000), in visual impact assessment (Fisher 1996; O'Sullivan and Turner 2001) and in urban landscape planning and design processes (Ranzinger and Gleixner 1997; Köninger and Bartel 1998; Kodmany 2000). Through the application of GIS to a visual impact analysis of urban redevelopment projects, it was found that valuable landscape resources could be prejudiced by the proposed projects (Oh 2001).
Forest and landscape management measures have impacts on the amenity value of forests (Steinitz 1990). Understanding impacts of planning policy in mountainous areas is often lost in the two-dimensional presentation. When it comes to visualizing how something will look before it is actually made, three-quarters of the general population just cannot see it. Two-dimensional representations, model boards and artist renderings have proven inadequate (Smith 1999). People may have certain attitudes towards management, in particular near urban areas (Tahvanainen et al. 2001). People believe they understand what a project will look like, but some time their perceptions are wrong. To facilitate this understanding new technologies, similar to that found in a flight simulator with an impact analysis extension, were developed to help people visualize change (Smith 1999). The development of computer tools for creating and representing virtual worlds has dramatically increased our abilities to comprehend some of the basic elements of the landscape and communicate them to audiences remote from the landscape under study (Orland et al. 2001). The speed and quality of generation of visual imagery, as well as the editing power computers offer, has already dramatically extended the capabilities in representing scenic views.
Digital modelling of vegetation is important for three-dimensional landscape visualisation. Vegetation can be modelled either at the level of individual plants or as a terrain texture. In order to achieve an even higher degree of realism, more and very detailed 3D-object-data and accompanying texture information would be necessary (Lange 2001). Computer graphics are playing an important role in giving lifelike information for the estimation of landscapes after finishing large-scale construction projects (Nakamae et al. 2001).
Three-dimensional imaging for characterization of environmental sites is beneficial in perceiving the whole picture and in making more efficient decisions because of the higher capacity in visualization. The citizens of many communities are often the visionaries and are ahead of the government officials in their interest in developing sustainable landscapes. The development of an interactive 3D visualization system will give the opportunity to the government officials and interested citizens to have a look on the results of planned projects before their implementation starts (Chan et al. 1998).
The present study presents the use of geographic information systems based, visualization techniques in the assessment of visual impact in the context of a management plan for some of forest development projects in high aesthetic value areas at the "Serra of Monchique", Portugal.
For the creation of the Digital Terrain Model (DTM) of the study area they were used topographic maps, land use maps, forest development and regional development maps and digital orthophotomaps from the Forest Service Department of Algarve. After the formation of the DTM it was prepared a visual landscape inventory where it was identified, classified and recorded the locations and quality of visual recourses and values of the study area (Serra of Monchique, Northwest Algarve). Digital maps of the visual sensitivity, visual absorption capability, existing visual condition and visual quality objectives from existing maps were also used.
On those maps was transferred the visual landscape unit boundaries and existing landscape alteration such as cutblocks and roads. These provided landmarks to facilitate positioning and sketching of the proposed operations. Key viewpoints were identified on the topographic maps. The GIS was used to find important observer locations based upon specified criteria and to visualise these strategic locations within a localized scene. Targeting analysis of scenery with respect to visitors was done through considering the most popular recreational activity and the viewpoints to which the visitors may be attracted. Scenic potential was measured by determining the number of viewpoints from which any terrain location is visible.
The location of key viewpoints selected in the office and identified on the field. At each viewpoint was taken pairs of photographs offset by few meters so a stereographic pair could provide a three-dimensional image that could be used for landform analysis. A Global Positioning System (GPS) was used to more accurately determine the coordinates of each viewpoint. It was estimated the visible portion of the proposed operations on the topographic base map. The visual impact assessment was conducted in every key viewpoint using the creation of digital landscape models after abstraction and simplification of the landscape in to its basic elements, terrain, vegetation and water.
The author introduces rendering techniques using computer graphics and video sequence images. The techniques were: computer generated images and montages for visualizing landscapes with photo-realistic rendering techniques, panoramic images and panoramic montages employing image-based rendering techniques made from video sequence images, and fly-over video composed with computer generated images that created after a digitalisation of a path in a 2D map display which was then traversed in the 3D scene. Computer simulations were used in indistinct and complex terrain and when one project proposal was visible from more than two viewpoints or when existed several alternative proposals visible from one or more viewpoints.
A Digital Terrain Model (DTM) was generated from digitised contour maps and the altitude of specific points in those maps (Ormsby and Alvi 1999). From the DTM was studied the potential intervisibility of the area and the view shed of each of the proposed forest development projects. Figure 1 shows the four forest development projects on the study area and the visible portion of the area from one observation point that is considered strategic since it is attracting high number of visitors every year. The above was repeated in every key viewpoint.
Figure 1. The four forest development projects on the study area and the visible portion of it from one observation point (striped was visible area).
For diagrammatic purposes the histogram of visible areas has been used to present the results as two groups representing visible and not visible areas. For this observation point it was used 100o visibility angle and maximum distance 5000 meters. Matos (2001) stated that maximum distance is an important factor that has to be taken in consideration in a view shed analysis, because the longer the distance the lower the visual impact that an object can bring to the landscape depending always on the size, form, texture, line and colour of it.
Figure 2 show a grid map with visibility attributes assigned to every cell as it can be seen in with a buffer zone of 2000 meters around the four proposed forest development projects. From that analysis could be seen what areas of the disturbed surface was visible from any position. For diagrammatic purposes the histogram of visible areas has been used to present the results as two groups representing visibility of all four projects and other areas. It was located all key viewpoints that fall into the 2000 meters buffer zone and a 3D computer visual simulation was generated for each one of them.
Figure 2. View shed analysis of the four proposed forest development projects. The shadowed area is showing what areas observers for any visible position of the disturbed surfaces can see.
Finally a video merging of the DTM and the scanned photographs was used to simulate the appearance of the proposed operations. Various digital fly-over videos were generated since they could be asked for public presentation and consultation due do high public concern and expectations. A photograph of one fly-over video made from the DTM of the study area can be seen in figure 3. The fly-over video was constructed after a digitalisation of a path in a 2D map display that was then traversed in the 3D scene. However, the 3D extension of Arcview was permitting to freely navigate in 3D space and to relate representations in 2D maps with 3D scenes synchronizing user interaction with the database model.
The above results were used to create a report for visual impact assessment so governmental officials that approve forest development projects could compare this report with the map of Visual Quality Objectives of the Algarve region. The report content included: maps, photographs and a copy of the visual landscape simulation (sketch, photographical manipulation and computer simulation).
Summarily, in the above report made for the key viewpoint shown in figure 1, it was concluded that only two of the four proposed forest projects where located in that area where the visual quality objectives were requiring retention or partial retention of the existing situation and had to be taken rigorous additional measures to decrease visual impact. The proposed measures for those two areas were: a) prohibition of clear cutting, b) timber harvest and post-harvest on site so leftovers could redistribute on the surface, c) prevention of any use of soil preparation machinery for reforestation, d) minimization of spontaneous vegetation handling, e) encouragement of natural revegetation. For the other two areas where visual impact was minimum and modifications were permitted from the visual quality objective, there were proposed the following measures: a) clear cutting only in patches parallel to the isolines, b) soil and spontaneous vegetation preparation without the use of heavy machinery, c) reforestation in patches or spontaneously excluding plantation in geometric unnatural lines.
The report and the evaluation method could help governmental officials to take the appropriate decision: accept, reject or suggest aesthetical modifications in any proposed project in the study area. Public consultation of proposed forest projects in areas with high aesthetic value could be facilitated if three-dimensional information of the virtual landscape would be transferred through the Internet by VRML technology (Rhyne 1999; Honjo and Lim 2001).
Figure 3. A photo captured from the fly-over digital video created from a digitalisation of a path in a 2D map display which was then traversed in the 3D scene aimed to visualize the location of the four forest development projects on the study area.
The methodology described above can be utilized both for the design of and for the public discussion on landscape planning. Similar visual landscape management plans could be made for the rest of the territory using the visual management plan for the mountainous area of Monchique as a model. Three-dimensional imaging for characterization of environmental sites is beneficial in perceiving the whole picture and in making better and quicker decisions because of the higher capacity in visualization. The link of geographic information database systems with object-oriented computer assisted design and the development of digital vegetation models will help to verify the visual quality objectives in any landscape reclamation project. The development of a 3D geographic information system will help to minimize the visual impacts of forest development projects on tourist attractions. At the same time the landscape ecology concepts of edge habitat, patches, fragmentation, corridors, connectivity and mosaics could be more easily understood and incorporated in the forest management planning in order to help the development of positive design.
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| [1] Faculdade de Engenharia
de Recursos Naturais, Universidade do Algarve, Campus de Gambelas, 8005
Faro, Portugal. Tel: +351966469029; Email: [email protected] |