Network Geography
The third major structural difference is the need to accommodate often extremely variable terrain conditions and accessibility issues during data collection (and, by extension, during data update and system maintenance). Relatively few local service companies comprise, at the daily operating level, such geographically extensive or topographically diverse areas as to preclude physical access by engineers in a one-day or one-week period. This means that data collection for local service companies is comparatively simple. Benchmarks tend to be readily recoverable and access is relatively easy, certainly compared with wilderness areas.
Corridor-based networks, on the other hand, are almost, by definition, located primarily away from centres of population, connecting settlements that depend on the corridors for the flow of some commodity (power, telecoms or petroleum, for example). Such corridors transect mountains, hills, swamps, lakes and rivers – indeed, the complete national or regional range of geomorphologic diversity.
This diversity of environments makes initial access difficult and updating problematic. It dictates that data collection be as complete as possible on the first site visit because of the cost of revisiting the corridor. It also recommends use of newer technologies such as digital photography, both still and video, to permit virtual ‘re-evaluations’ of route options subsequent to the actual survey, inventory and mapping visit. This diversity of environments also recommends the application of several specific GIS technologies for data capture. The first and, given its ubiquity, most significant technology is aerial photography using inertial measurement units and the full range of GPS tools. While ground control is a critical component of the survey process in either situation, the relative lack of monumentation along rural corridors makes the use of GPS – both on board the aeroplane and in the field – a virtual necessity. The second technology, which incorporates the first, is the use of light detection and ranging (LIDAR) sensors for detailed corridor-mapping. The extraordinarily high resolution of contemporary LIDAR offers an unprecedented ability to capture details such as the actual sag and height above ground level of transmission lines. This, in turn, permits the development of a new generation of applications for the GIS that further assists with cost justification. The costs of using LIDAR as a data collection tool have become substantially lower in recent years, which has further encouraged deployment.
Another technology that is appropriate for corridor- mapping is three-dimensional (3-D) visualisation. Interactive 3-D models and databases may be created from existing digital spatial data (for example digital imagery, elevation models and feature coverages). These interactive 3-D databases may be used, in turn, to provide 3-D visual simulations and to aid decision support applications. This is a particularly valuable tool in situations where multiple routes are under consideration.
The fourth technology is hyperspectral image analysis. This branch of remote sensing offers support for analysis of such variables as local weather, agriculture, forestry/rangeland, land resource management and environmental management. In the context of corridor-mapping, the specific analyses will be driven by the target applications. In any case, the fundamental analytical capabilities of hyperspectral image analysis have significant implications for corridor-mapping and GIS.
Other Issues
These technical variations dictate the use of appropriate technologies during data acquisition and map production. In addition, there are several other requirements for corridor-mapping that extend beyond the structural differences outlined here. Corridor-planning and mapping require an awareness of the human and natural environment, as well as an evaluation of engineering considerations. Achieving this awareness requires an interdisciplinary team that includes engineers, planners, geographers, biologists, hydrologists and environmental scientists, sharing the goal to recognise social and environmental concerns as early as possible.
Timely recognition of critical issues permits consideration of social and environmental concerns early in the planning process, rather than demanding impact mitigation after the fact. For each discipline, GIS technology serves as a backdrop for the collection, management, storage and retrieval of relevant information.
Category:
Transportation
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