Analysis of roundel visibility in GIS environment (original) (raw)
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Digital Elevation Models: Terminology and Definitions
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Digital elevation models (DEMs) provide fundamental depictions of the three-dimensional shape of the Earth’s surface and are useful to a wide range of disciplines. Ideally, DEMs record the interface between the atmosphere and the lithosphere using a discrete two-dimensional grid, with complexities introduced by the intervening hydrosphere, cryosphere, biosphere, and anthroposphere. The treatment of DEM surfaces, affected by these intervening spheres, depends on their intended use, and the characteristics of the sensors that were used to create them. DEM is a general term, and more specific terms such as digital surface model (DSM) or digital terrain model (DTM) record the treatment of the intermediate surfaces. Several global DEMs generated with optical (visible and near-infrared) sensors and synthetic aperture radar (SAR), as well as single/multi-beam sonars and products of satellite altimetry, share the common characteristic of a georectified, gridded storage structure. Neverthele...
Advances in Digital Terrain Analysis: The TADTM Initiative
Lecture Notes in Geoinformation and Cartography, 2000
Digital terrain modelling has been one of the most active research and application fields in geo-spatial information science and technology. Using the techniques of computer graphics, the land surface, or terrain surface, can be represented digitally using large volumes of regularly or irregularly distributed sample points, instead of solely relying on the traditional contours or other cartographic symbolism. The term digital terrain model (DTM) is now widely recognized as the digital representation of the terrain surface for a given geographical region.
Making and interpreting digital terrain model
Research Journal of Agricultural Science, 2013
Surface modeling is the process of plotting a natural or artificial surface through one or more mathematical equations. Modeling land surface modeling is a particular case of the areas that need to be taken of the specific issues related to the representation of the earth or parts of it. Digital model of an object or phenomenon, consists of a collection of data stored systematically (database) describing a three-dimensional coordinate system, arbitrary or particular characteristics of the object or form their states / achievements phenomenon (conversion as digital image) and allow adequate computer programs deduction form and characteristics of the object or phenomenon achievements Star new points. Digital model of the terrain is a "tool" information consisting of field data and software is a key component of a GIS. DEM consists of an ordered set of planimetric position information and share the points that describe the spatial configuration of the structures carrying reli...
Over the years the study and accurate determination of point elevations and topographic forms of land spaces and sea beds have been the exclusive preserve of Surveyors, Geodesists and Hydrographers and in a derivative sense, Cartographers. Research into diverse environmental phenomena is growing by the day as continuously improving credible results are obtained from computer based Digital Terrain Analysis (DTA), leading to fundamental shifts in engineering solutions and designs and social options in managing the environment. Digital Elevation Models (DEMs) are basic input for the development of Digital Terrain Models (DTMs) which seeks to classify terrain characteristics and behavior for prediction of future environmental phenomena. A continuous digital topographic data structure, the DEM, is foundational to efficient analysis of the landscape as is needed in line of sight determination and in the analysis of topographically influenced environmental phenomena such as, flooding, erosion, stream flow, sediment transportation, runoff distribution etc. The growing efforts today are to express topographic data in continuous digital data structures that either assign an elevation value to every unit of land space, usually in fixed cell sizes, or provide the basic data and algorithm for continuous computation of irregularly sized and sloping triangles across the landscape. These new efforts are purely computational. They are however extending the use of topographic analysis in other vastly expanding areas such as 3-D computer graphics for anatomy and surgery, 3-D movie creations, and 3-D computer printing. A basic fact that makes the involvement of Surveyors imperative in Digital Elevation Model research and development is the proficiency required for adaptation of different geoid models, issues of topo data source scales and accuracy and data geolocation. This paper reviews a few steps of processing different traditional topo data structures to Digital Elevation Models. It makes a few comparisons between the evolving DEM forms and discusses a some applications of the DEM in environmental phenomena analysis. The paper concludes with a call for Surveyor scientists to take their rightful place in the research efforts to move from topographic data structure of discrete spot heights or firm contour lines to dynamic forms of continuous digital topographic data structure, the DEM. A further imperative of this paper is the need to review topographic surveying training curricula to equip upcoming Surveyors with the required skills for DEM development.
What should a bare earth digital terrain model (DTM) portray?
National mapping agencies in North American and western Europe have released free lidar point clouds with densities of 2-23 points/m², and derived terrain grids. Geomorphometric processing uses a bare earth digital terrain model (DTM), which can be acquired from mapping agencies or created from the point cloud to better control its characteristics. Free software provides tools for noise removal, ground classification, surface generation, void filling, surface smoothing, and hydraulic conditioning. Tests with three ground classification algorithms, and four surface generation algorithms show that they produced very similar results. The main issues for geomorphometric operations on DTMs involve whether the highest and lowest ground points should be in the DTM if they are not on a grid node, how water, buildings, and roads should be treated, if using a DTM of lower resolution will effectively filter out noise and allow much faster processing, and if lower resolution DTMs should be crea...
Modern Methods of Implementation and Interpretation of Digital Terrain Model
2016
Modeling land surface is a particular case of modeling the areas which need special consideration for specific issues related to Earth representation or some parts of the terrestrial crust. This study had as main objective the achievement of a digital terrain model in a mountain area based on Triangulated Irregular Network (TIN). This studied area represents a part of the Retezat Mountains. The images obtained were analyzed with ArcGIS software. The database and algorithms used facilitated the creation of a 3D model for the studied area, with a spatial distribution similar to the real situation in the field. The obtained 3D model facilitated the graphical representation of different types of slopes, grouped into 6 classes at intervals of 10 units, according to slope values, covering 100% of the study area. The largest coverage consists of land with slopes between 10-40%. The 3D model also facilitated graphical and numerical representation of aspect and it allowed the Hillshade model...
Encyclopedia of Geographic Information Science (Terrain Analysis)
Terrain analysis uses elevation data, especially digital elevation models (DEMs), to characterize the bare terrain surface and, in most cases, link terrain properties to the natural or built environment. Closely associated with spatial analysis, terrain analysis is a fundamental component of geographic information science and provides solid support for a wide variety of GIS modeling and analysis activities. Terrain analysis is built upon terrain surface characterization, as well as the easy accessibility and high quality of terrain data.
DIGITAL TERRAIN MODELING IN A GIS ENVIRONMENT
Digital terrain models (DTMs) in recent times have become an integral part of National Spatial Data Infrastructure (NSDI) of many countries world-wide due to their invaluable importance. DTMs play a major role in hydrologic modeling, sediment transport, soil erosion estimation, drainage basin morphology, vegetation, and ecology. DTM generation however has a setback of high cost of primary data input acquisition (i.e. elevation) and complexities in processing. Most DTM data are derived from photogrammetric data, satellite image data, laser scanning data, cartographic data sources, and ground surveys though accurate is expensive, timeconsuming and require skilled personnel. This paper describes a low cost means to generate DTMs where elevation data is not readily available in digital form and when the accuracy of the output is not a dominant factor. The existence of large volumes of hardcopy topographic maps provides a source of primary input in the form of contours which can be digitised and used for DTM generation purposes. This research therefore aims at generating DTMs within a GIS environment using elevations digitized from topographical maps. That is, a geographic information system (GIS) based approach is presented for the development of a terrain model. After digitizing contours and points along contours from a topographic map, various interpolation algorithms were used to generate DTMs and their accuracies in terms of root mean square errors were assessed. The resulting surface model provides a good representation of the general landscape and contains additional detail information (such as slope, aspect, cross-sections, volumes, hillslope) to describe, evaluate and quantify terrain properties. Also, if the digital contours are geo-referenced, they can be readily integrated into existing GIS for 3D surface visualization and spatial analysis. Results of surface analysis (intervisibility analysis) are presented and among other applications, the DTMs proved useful in surface analysis.
Enter the Past ] -USE AND ABUSE OF DIGITAL TERRAIN/ELEVATION MODELS
DTM's and DEM's are widely used for landscape reconstruction and GIS analysis. Very accurate models are possible to construct on a small scale with the aid of a 3d-scanner, or on a larger scale with the aid of photogrammetic processing of aerial images. But far more often archaeologists will have to rely on software to process point-data and contour lines. The different kinds of software have many algorithms and parameters. They have to be used with care, as changing an algorithm or the parameters for an algorithm, will dramatically alter the resulting DTM or DEM. Especially if the model is used for further GIS analysis, any lack of knowledge on these differences may have serious repercussions on the conclusions of for instance site-locations and ways of communication. Ken Kvamme already demonstrated these possible dangers almost a decade ago. Since then, many new and more elaborate algorithms came available, capable of both creating a better model as well as an even more distorted image of reality. This suggests that archaeology may benefit by an update on this subject.
The influence to source of data for accuracy on digital terrain models (DTM)
Glasnik srpskog geografskog dru?tva, 2005
Садржај: У раду је дат преглед савремених метода прикупљања података за потребе израде Дигиталних Модела Tерена (ДМТ), као и тачност података која ове методе обезбеђују. На примеру дигиталног модела добијеног дигитализацијом картографског садржаја основне државне карте, и теренских мерења ГПС технологијом и аерофотограметријских мерења приказан је поступак оцене оваквих база података о рељефу.