Geodesia et Descriptio Terrarum (Geodezja i Kartografia) 12 (4) 2013
VISUALIZING THE RESULTS OF HYDRODYNAMIC MODELING USING GIS 3D SYSTEMS
Edyta Hadaś, Przemysław Tymków
hydrodynamic modeling, GIS, 3D, ISOK
The Polish national IT crisis management system for protection against extreme hazards (ISOK), which was created to increase the protection of people and property, produces two-dimensional data. The development of information technology has made it possible to visualize spatial data using 3D GIS systems. However, detailed visualization requires the integration of spatial data that comes from different sources, e.g. from direct land-surveying measurements, laser scanning data, aerial photography, orthophotomaps and other photogrammetric products, as well as sites from various databases, in particular from topographic databases. This paper presents a concept and the results of three-dimensional visualization of hydrodynamic modeling for a section of the Widawa River valley. The digital terrain model from airborne laser scanning was used and was overlaid with the texture of an orthophotomap. Spatial data was supplemented with three-dimensional models of buildings and trees that were taken from the publicly-available Google 3D Warehouse gallery. Visualization of the hydrodynamic modeling was done using the constructed spatial model. The integration and visualization of data was performed in ArcGIS software using the ArcScene module.
THE IDENTIFICATION OF WATER BODIES AS BDOT10K OBJECTS IN A LASER SCANNING POINT CLOUD BY MEANS OF AN ALPHA-SHAPED ALGORITHM
Małgorzata Mendela, Andrzej Borkowski
Key words: airborne laser scanning, Database of Topographic Objects (BDOT10k), α-shaped, boundary detection, body of water
Airborne laser scanners (ALS) usually rely on a near-infrared light beam which is absorbed by water. This produces empty areas with no points in the LiDAR dataset (gaps, laser shot dropouts). Detecting the boundaries of bodies of water in a LiDAR dataset can thus be seen as the identification of boundaries of empty areas. The method for the identification of water bodies could be used to update and supply the Database of Topographic Objects (BDOT10k). The x, y co-ordinates of ground laser points of the previously classified LiDAR point cloud of the 4 points/m2 nominal density were used to detect bodies of water. The automatic identification of bodies of water was performed by the means of an α-shaped algorithm. Numerical experiments were conducted for 16 tested sites, which were bodies of water. The accuracy of boundary identification was evaluated by comparing the results with those seen on orthophotos with a pixel size of 0.10 m. Based on the maximum deviation values of the measured results, it has been shown that bodies of water were identified on average with 95% accuracy and the boundaries of 62% of the tested sites were delineated with 100% efficiency. Furthermore, the studied algorithm has a featured mechanism that enables it to eliminate single, random points distributed on the surface of a body of water. The proposed method can be used as an additional source of BDOT10k, especially for bodies of water whose banks are covered with vegetation which are difficult to identify on orthophotos.
CARTOGRAPHIC IMAGES OF MENTAL MAPS OF A CITY, PRESENTATION AND ANALYSIS USING GEOGRAPHIC INFORMATION SYSTEM SOFTWARE
mental maps, cartographic methods of presentation, GIS, structural mapping
This paper describes the use of mental maps to evaluate users’ spatial awareness of a city, taking Lublin as an example. Students living both within and outside the town of Lublin were interviewed, making it possible to analyze the influence of place of residence on the knowledge of spatial areas at either a general and more detailed level. An additional goal of the study was to evaluate the usefulness of Geographic Information System software in this type of research. Sketches were analyzed for quality and quantity, with emphasis placed on linear features and landmarks. The graphic outcome of the results and the analysis was done using GIS, along with a critical evaluation of using the approach for implementing cartographic methodology principles (for a cartogram and the sign method). The results identified the features that were most commonly recognized by the users of a space. The results demonstrate that there are serious limitations in the map editing process when done with correctly applied methodology.
This article presents a practical analysis of the ways geodetic instruments are tested in accordance with the standards of ISO 17123, seven of which have been translated into Polish and adopted as standards in Poland. The standards recommend that measurement tests of instruments be carried out prior to instruments being used for particular work. The objective of testing is to verify whether measurement accuracy of a given instrument agrees with the level of accuracy guaranteed by the manufacturer. The article provides information on methods of testing geodetic instruments in accordance with the procedures described in the standards. Techniques for establishing field tests for various kinds of instruments are presented with special attention on the statistical analysis of the tests results. Although the standards do not provide for changes to the organization of testing fields or calculation programs, suggestions are presented for modifying certain parts of the standards. When suggestions are received for making amendments, ISO introduces updated standards replacing the former standards that were in question by users. In this way, two of the 17123 series of standards were revised in the English version. They have not yet been translated or adopted into the Polish standards.
The vertical comparator which was built in the Geodetic Metrology Laboratory of the Faculty of Mining Surveying and Environmental Engineering of the AGH University of Science and Technology in Krakow is used to determine the precise calibration corrections of invar, fiberglass and technical rods, depending on user requests. The paper presents the results of the calibration of selected types of barcode rods known as engineering levelling rods – folding, uniform rods made of fiberglass designed for Leica and Topcon levelling instruments and folding rods made of wood for Trimble DiNi levelling instruments. Based on the results of calibration, an analysis of graduation errors was performed for different types of rods. For folding rods, large errors in graduation of up to 0.3 mm were found upon contact with elements. Errors were found to be cumulative when readings back and forth were performed on different segments of the rods or when there was a large difference in the height between points. The coefficients of scale for various sections of the rods varied considerably. The paper assesses the suitability of engineering rods for measuring a detailed levelling network, including measuring the configuration of the terrain on which the levelling is performed.