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:: INTERACTIVE VISUALIZATION OF TERRAIN MODELS AND ORTHOPHOTOS. Lionel Dorffner, assistant professor

Document type:: Monograph

Structure type:: Chapter

triangular irregular network (triangulation including all measured points - breaklines and formlines are maintained in the stored data, full 3D is possible, much greater data amount as for regular grids) hybrid structure (regular grid with additional information about breaklines and formlines, also combination with TIN areas is possible) [Kraus K., Jansa J., Kager H., 1997] The quality of the computed orthophotos also depends a lot on the used DTM. Concerning orthophotos for small scale (pixelsizes greater than 10 m) a regular grided DTM will be sufficent to obtain good results. For large and medium scale orthophotos the used DTM should also consist of additional structure information. If orthophotos with pixelsizes of 1 m or less have to be generated also buildings must be taken into account. 2 VISUALIZATION Digital terrain models and orthophotos are widely used and a lot of products can be derived from them (isolines, profiles, perspective views, intersection with other data, volume calculations). Such results are used either as the basic information for further analysis or as final plots for visualization and presentation (Figure 1). Figure 1 DTM representation of isolines, breaklines, formlines and outlines of buildings. Depending on the object information and level of complexity there are different levels of visualization for the derived products mentioned above (wire frame, shading, texture mapping, integration of other data such as roads, buildings or thematics). All these outputs can be produced with high quality and accuracy and therefore are suitable for a lot of applications. A disadvantage of these outputs is the lack of flexibility. A shaded and texture mapped perspective view of a DTM is a very illustrative tool for giving a more realistic appearance to landscape and larger areas, but it is still a static view of a much more complex model. To show the complexity, a lot of different plots from different points of view have to be created. In some cases, especially when discussing with customers and sponsors, it is of the same importance to present results in an appropriate and more impressive way. Imagine your customer can move over the DTM and explore and analyze the model in real time! As in today's world everything is rotating and moving it seems obvious to look for a possibility to perform interactive, dynamic, real time DTM visualization and animation. The problems that arise are not issues of basic algorithms (computer graphics has reached a high level of sophistication), they are rather problems of handling very large data sets under time- constrained conditions. Some of the requirements for efficient visualization are distributed worlds, levels of detail and image compression. "Distributed worlds" means that the whole DTM is divided into different parts, each one representing an own smaller DTM. So, only the visible parts (determined by using a viewing pyramid) need to be loaded. Using this concept, the amount of data to be hold in memory at the same time can be reduced by approximately 75 percent on average. A further increase of performance can be achieved by utilisation of levels of detail (LOD). "LOD is a mechanism used in computer graphics to improve the drawing speed of complex scenes [Clark J.H., 1976]. Each object is stored several times in different levels of quality (levels of detail). During visualization each object is drawn in the optimal level of detail. The chosen level depends on the size of the object in the current view. Objects that appear small can be drawn in little detail (and therefore very fast) without loosing quality; in contrast, objects near the point of view that cover a lot of space on the screen need to be rendered in full quality." [Kofler M., Rehatschek H., Gruber M., 1996]. Although the total amount of data is increased by storing different LOD in a pyramid structure, the current memory demand during interactive visualization can again be reduced dramatically. As a last way of data reduction, image compression should be mentioned here. When visualizing a DTM

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