International cooperation and technology transfer

Fras, Mojca Kosmatin

Bibliographic data

Monograph

Persistent identifier:: 856490555

Author:: Fras, Mojca Kosmatin

Title:: International cooperation and technology transfer

Sub title:: Ljubljana, Slovenia, February 2 - 5, 2000 : proceedings of the workshop

Scope:: VI, 163 Seiten

Year of publication:: 2000

Place of publication:: London

Publisher of the original:: RICS Books

Identifier (digital):: 856490555

Illustration:: Illustrationen, Diagramme

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: GEOMORPHOLOGIC IMPROVEMENT OF DTM-s ESPECIALLY AS DERIVED FROM LASER SCANNER DATA. D. Gajski

Document type:: Monograph

Structure type:: Chapter

70 GEOMORPHOLOGIC IMPROVEMENT OF DTM-s ESPECIALLY AS DERIVED FROM LASER SCANNER DATA D. Gajski Institute for Photogrammetry, Faculty of Geodesy, University of Zagreb, Kaciceva 26, 10000 Zagreb, Croatia Key word: laser-scanner, DTM, water flow analysis Abstract Recent advances in laser-scanning techniques made it to a most attractive method of data acquisition for digital terrain modeling. This is due not only to the impressive level of automatization but also to the increasingly high density and precision of the points. Methods of filtering data in a preprocessing stage allow for interpolating a DTM very closely describing the terrain surface. Further improvement of the géomorphologie quality of the surface thus interpolated can be achieved by deriving structure line information of it and introducing it as constraints into a final step of interpolation. A raster type water flow analysis is described and applied, allowing to derive the structural information needed. The impact of these constraints is then considered. Applying the method as proposed to DTMs based on data acquisition techniques other than laser scanning may also be of advantage. A test area, a part of the Vienna Woods has been chosen. Water flow analysis is performed by SCOP.MATRIX within the frame of an alpha version of the SCOP_DTM_XX digital modeling system to come. 1. Introduction Airborne laserscanning provides the means for measuring polar coordinates i.e. directions and distances between fixed-wing or rotary-wing aircraft and the reflecting objects on the earth’s surface. When the outer orientation of the sensor during the scanning is known, then the measured polar co-ordinates can easily be converted into Cartesian WGS84 because of the use of GPS and INS for determining the elements of outer orientation. To transform laser points into local (national) coordinate system, the geoid undulation has to be very well known. This transformation requires data resampling which might be done either by an interpolation technique or by the nearest neighbour method. Depending on the density of the measuring points and the width of the target grid, the resampling will cause the position and elevation errors which can only be ignored for plain and unstructured surfaces. For high quality DEMs resampling errors must be minimized - which means that there should be at least two limes more measurements available than needed for the target grid. and interpolation to laser scanner data (such a method is described in Kraus et al., 1998) However, the contours derived from a thus filtered and interpolated laser scanner DTM will have low géomorphologie quality. Geomorphological constraints into post-processing of laser scanner data will be included here. 2. Motivation The hydrological and geomorphological tradition suggests that fluvially dominated landscapes rarely contain pits since the process of water transport and erosion precludes their development. Hydrological models that transfer water over and ultimately off a surface often fail to perform if that surface contains pits from which water may not be removed. As a consequence elevation models are often pre-processed in some way to remove such ‘spurious’ pits. (Wood, 1999) 3. Theory and algorithm The final quality of DEM based on laserscanning is also influenced by the shadowing effect, because in built-up or forested areas a flat viewing laserbeam will reflect mostly walls or treetops and will rarely reach the ground. In the postprocessing, shadowed areas have to be recognized and measured points classified on the basis of points belonging to groundfloor, as well as those not belonging. The final quality of DEMs based on laserscanning can be improved largely through applying a qualified filtering Pits are areas that lie lower as surrounded terrain surface. The lowest point of depressions is point that lies in a local concavity (all neighbours higher) and can be described by second derivatives as: d 2 z dx 2 <0, f?<0 dy (1)

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