DEM datasets are getting larger and larger with increasing precision, so that approximating DEM can be useful in some situations. Conventional terrain simplification algorithms try to minimize the elevation error between the simplified and the original terrains [3]. This project tries to minimize the visibility error in terrain approximation. The error metric is defined as the average viewshed ...

Calculation of the viewshed from a digital elevation model (OEM) is a common capability of a GIS packages. Two mistaken assumptions are made, however: first, that the OEM is accurate, and second that the viewshed is a Boolean phenomenon. The inaccuracy of the OEM data is acknowledged in reporting of the root-mean-squared error. The mistake of the Boolean viewshed is recognizable in the real-wor...

One of the most widely available procedures packaged with CIS for the analysis of a Digital Elevation Model (DEM) is the identification of the viewable area, or the viewshed. The elevations recorded in the DEM do, however, contain error, and the USGS, for example, publishes a Root Mean Squared Error (RMSE) for each DEM. Research reported here assesses the uncertainty of locations being within a...

Water quality and freshwater fish diversity from nine waterfalls at Khao Luang National Park, Thailand was examined. Streams were shallow, fast flowing with clear water and rocky and sandy substrate. The mean water quality of waterfalls at Khao Luang National Park were as following pH 7.50, air temperature 24.27 °C, water temperature 26.37 °C, dissolved oxygen 7.88 mg/l, hardness 4.44-21.33 mg/...

This paper describes a method of calculating the inherent visibility at all locations in a landscape (‘total viewshed’) by making use of redundant computer cycles. This approach uses a simplified viewshed program that is suitable for use within a distributed environment, in this case managed by the Condor system. Distributing the calculation in this way reduced the calculation time of our examp...

Views of two man-made

Users of GIS are faced with the ongoing and difficult problem of estimating the validity of a GIS output given the uncertainty of the quality of cLgital mapped data. This research project examines the manner in which error from a digital elevation model (DEM) results in error in an estimate of a viewshed. The data set includes two DEMs for the same study area. A 10-metre DEM serves as the contr...

In this study, we carry out viewshed analysis to landscape voxel models derived from airborne laser scanner data. The objective is to make comparisons of viewshed analysis with different voxel models; the ground model representing the bare Earth, the surface model including also all above-ground features, and the combined model, which is formed from the ground model and the laser measurements i...