Nowadays, there is a huge volume of data about terrains available and generally, these data do not fit in the internal memory. So, many GIS applications require efficient algorithms to manipulate the data externally. One of these applications is the viewshed computation that consists in obtain the visible points from a given point p. In this paper, we present an efficient algorithm to compute t...

The selection of the minimal number of observers that ensures the maximum visual coverage over an area represented by a digital elevation model (DEM) have great interest in many fields, e.g., telecommunications, environment planning, among others. However, this problem is complex and intractable when the number of points of the DEM is relatively high. This complexity is due to three issues: 1) ...

This paper examines the effects of database generalization on the area which is determined to be visible in GIs analysis. Many different methods of generalization are possible, but here, for any cell at the target resolution, elevations are determined from: the arithmetic mean, the maximum, the minimum, and the maximum difference from the mean of the cells within the kernel, and all possible co...

introduction conservation and management of landscapes and beautiful sceneries is one of the necessities of establishing and maintaining the protected areas. analysis of landscape visual quality has an important place in landscape planning and designing. in this way, reviewing effective criteria and discovering the simple patterns which affect the landscapes is the most important step of modeli...

Flow characteristics are a prominent factor determining body shapes in aquatic organisms, and correlations between body shape and ambient flow regimes have been established for many fish species. In this study, we investigated the potential for a brief period of extreme flow to exert selection on the body shape of juvenile climbing Hawaiian gobiid fishes. Because of an amphidromous life history...

We describe several programs working with 1201x1201 gridded (array) terrain elevation data: determining the viewshed of an observer, and the visibility indices of all points, converting from a grid to a TIN, losslessly and lossily compressing a grid, and interpolating from contours to a grid. The intent is to integrate these, and new, programs, into a test suite the better to understand hypsogr...

We describe several programs working with 1201x1201 gridded (array) terrain elevation data: determining the viewshed of an observer, and the visibility indices of all points, converting from a grid to a TIN, losslessly and lossily compressing a grid, and interpolating from contours to a grid. The intent is to integrate these, and new, programs, into a test suite the better to understand hypsogr...