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:: DIGITAL AUTOMATIC ORTHOPHOTO PRODUCTION WITH LASER LOCATOR AND AERIAL PHOTOGRAPHY DATA. Evgueny Medvedev

Document type:: Monograph

Structure type:: Chapter

120 1) Obtaining the coordinates. 2) Photo triangular spreading net of ground control points. 3) Aerial photos external orientation. 4) DTM production. 5) Aerial photos projection on DTM, contours identification. From mathematical point of view, stages 2 through 4 are an integral process which essence consists of establishing correlation and calculation parallax in stereopairs, only may be done in sequentially stereopair by stereopair, that inevitably accumulates geopositioning error as the distance increases from the true, geodetic specified ground control points. Plus, nothing is principally changed in terms of resulting accuracy, with usage of automatic correlation methods for mutual photos orientation, instead of manual, as well as DTM production with digital photogrammetry systems instead of relief depicting via visual stereo measurements. Another issue is utilizing GPS receivers in aerial surveys for registration of principal point spatial coordinates. Availability of such data, though significantly improving the situation (due to reduction of stereomodel mobility during spatial orientation), nevertheless can not be deemed sufficient for full automation of stereotopography process. 2) The second category of problems consists of variety of well known particular limitations of stereophotogrammetry method. These are studied in detail therefore it is no sense in thorough description here. Let us just mention the following. The problems of such nature are quite diverse in their characters, but they all are in general tied with issue of points correlation on stereopair. In certain cases this leads to complete inapplicability of the method, for instance in snowed or sanded landscapes with a full absence of visual texture. In other cases this problem puts the results' quality in dependence on the number of factors like average forest elevation and density when surveying forestry, or buildings shape when mapping city landscapes. Limitation of stereophotogrammetry method emerges mostly in the most practically meaning applications connected with survey of complex and full of objects scenes. Particularly due to this reason, large-scale mapping of city landscapes with significant share of multilevel buildings can not be done by exclusively aerial survey methods, thus forcing massive involvement for this goal carrying out of on-ground topographic survey, extremely expensive in city conditions. Besides, there are season limitations restricting aerial surveys in presence of significant snow cover or vegetation with leaves. For most part of the Russian Federation such limitations only leave 1.5-2 months a year for aerial survey. Practically, such problems often lead to the serious deformation of technology that causes doubts about results correctness. Thus, production of DTM of a big city area considered as compulsory within stereotopography method, is deemed such a labor consuming and expensive task affecting the overall cost of project that a 'compromise' is offered to use a relief model taken from existing topographic map of appropriate scale. Given the extremely low metrologic quality of existing topography basis in Russia, it is only left to guess what consequences in future would be caused by such decisions when doing, for example, a cadastre system to regulate real estate relations. 2. METHODIC PROBLEMS OF JOINT APPLICATION OF LASER LOCATOR AND PHOTO DATA Advantages of laser locator methods in DTM production are commonly recognized. However, this does not limit the meaning of laser location in topography. Consistent development of idea of combination laser locator and digital photo aerial survey data makes it reasonable to hope on almost fully automatic technology of aerial survey data processing for topographic material production. 2.1. Digital Terrain Model DTM itself obtained with laser location method, has a number of obvious advantages comparing with classical stereophotogrammetric DTM: ♦ Traditionally the accuracy of absolute georeferencing on WGS-84 spheroid is considered as a main advantage. Laser scanners (locators) manufacturers usually declare an accuracy of 15-30 cm on geodetic elevation. This value is generally determined by achievable accuracy of range signal measurement with appropriate electronic unit. Guaranteed planimetric accuracy is specified in proportion to survey altitude, and normally ranges from 1/1000 to 1/2000 of flight altitude, that refers to value of 25-50 cm for typical altitude of 500 m. It is clear that above values satisfy accuracy requirements for the most large-scale topographic maps. It should be mentioned, however, that these evaluations are not unconditioned, and only achievable in the most favorable survey conditions. Such accuracy of georeferencing can not be achieved with any other remote sensing equipment. This determines a major difficulty in attempt of experimental verification - practically the only way of such verification is low-productive differential GPS on-ground measurements.

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