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...

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...

in this article, a study is made to demonstrate the possible utilization of hydrological anergy resources, contained in small water streams and water falls. the total energy, which could be recovered without extensive investments, has been estimated. it is shown that, the energy produced shall meet the total energy requirements of the rural areas of the country. a hystorical background of the u...

Solar Radiation is considered as an important parameter in modeling environmental, hydrologic and biophysical processes. One of the reasons that solar radiations are not extensively used in models is the problem of its measurement in different points. Solar Analyst Viewshed Algorithm makes possible calculation of the topographic effects on solar radiation at local and landscape scales. With res...