The assessment of the visual perception in viewshed analysis for the landscape settings

Abstract

Visibility studies for rural and forest landscape are well established and conducted by means of standard GIS tools that compute the viewshed (a binary representation of the visibility of a location from a certain viewpoint) and cumulative viewsheds (integer representations of the visibility of a location from more viewpoints obtained with raster algebra). However, in order to go beyond the sole geometric information if a cell is visible or not, some authors have introduced various concepts that are based on the visual magnitude or visual exposure. These concepts also take into account the target magnitude, the atmospheric extinction, the colour difference to the background and the visual acuity. These calculations may be complex, extremely time consuming and not affordable with standard GIS tools, because they require specific programming tools. Besides, depending on the application, the factor that affects the visibility may be the distance, the atmospheric extinction, the contrast, etc. In this work, we concentrate on the problem of the calculation of the landscape sensitivity, which defines the degree to which a given landscape is potentially affected by possible changes by means of viewsheds analyses. An example in rural settings is presented in order to demonstrate the problems that arise in real applications and the possible solutions.

Prehistoric Panopticon: Settlement Visibility at Ancient Cahokia Mounds

“…This distance range is similar to what is known about the geographic extent of the main portion of Cahokia (Pauketat, 2004). Yet visual acuity should be taken into account for viewshed accuracy (Fabrizio & Garnero, 2013) and analytical extent. Scholars have estimated 6.2 km as the maximum distance at which humans can distinguish objects under optimal conditions (Higuchi, 1983; Friedman, 2008; Wheatley & Gillings, 2000).…”

“…Since the early 1990s, archaeologists have made use of computer technologies, such as GIS, to calculate line of sight between locations (Boaz & Uleberg, 2000; Kantner & Hobgood, 2016; Petrie, Johnson, Cullen, & Kvamme, 1995; Swanson, 2003; Wright, MacEachern, & Lee, 2014), accounting for variations in the terrain and curvature of the Earth as well as other features that may affect visibility (Fabrizio & Garnero, 2013; Ruggles, Medyckyj-Scott, & Gruffydd, 1993; Whitley, 2008). Given the potential of 360 degrees of vision by an observer, these visibility analyses are ideal for evaluating a Panopticon design (Kay & Sly, 2001).…”

“…One measure of site visibility, termed a viewshed , identifies the portions of a landscape that are visible from a single point or a particular set of locations. Viewsheds can be rendered to represent all areas that are visible from the perspective of an individual or can be adjusted to account for the relative ability to differentiate features within different distance ranges (Fabrizio & Garnero, 2013; Higuchi, 1983; Ogburn, 2006; Marsh & Schreiber, 2015; Randle, 2011; Wheatley, 1995). For an assessment of a Panopticon design, however, the mere threat of surveillance is what drives behavior.…”

Visibility analysis in urban spaces: a raster-based approach and case studies

“…In order to study the visibility of an out-of-scale building within an urban environment it is necessary to use GIS procedures that consider together both terrain and built environment representations and model the interaction between humans and the space. However, visibility studies, especially those referring to rural and forest landscape analysis (Fabrizio and Garnero, 2013), are usually based on terrain representations only such as triangulated irregular networks or a regular square grid of elevations [digital elevation models (DEMs)] and require some simplifications in order to take into account vegetation and other obstacles that affect the visibility (eg, create a vegetation elevation model that is added to the DEM).…”