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

121 An additional difficulty is that manufacturers of laser equipment specify measurement accuracy not as an extreme but statistic value due to which big number of control measurement is required for the correct assessment. Given that the resulting accuracy obviously depends also on surveyed object type (actually on the condition of its surface), the task of true accuracy verification turns into quite a labor consuming one. The results of thorough investigation in this field are available in (Murtagh, 1999 and Piwowar,1999). An important factor influencing resulting accuracy of laser locator measurement, besides, obviously, technical features of laser locator itself, is a quality of GPS signal used to register an aircraft trajectory. In this regard, it is worth mentioning that: 1) There are areas overall unfavorable in terms of GPS measurements quality. This may be both caused by unfavorable satellites configuration, and the number of other factors as well. The worst situation (among the countries the author had experience in) is in Italy. The favorable on number of satellites and working constellation periods fall in the night time, as a rule, when aerial survey is impossible. Mountainous relief greatly shields the satellites. But the major problem is a big number of radio repeaters complicating GPS signal receipt up to its full loss. 2) Accuracy of trajectory data obtained with cinematic GPS measurements is directly tied with piloting quality. The issue is that required accuracy of 10-15 cm may be provided with only special double-frequency carrier phase GPS receivers, working in regime of continuous tracking of active satellites. Any abrupt evolution of aircraft or appearance of relief obstacle in the upper hemisphere may lead to loss of the working constellation and failure of tracking as a result. Resumed coverage and tracking may take up to several minutes as they require a sophisticated procedure of infinity resolution on whole wavelengths. Up to that moment the registered data shall be absolutely unsatisfactory on accuracy. Moreover, even for trajectory portions with quality GPS receipt, the correct results are only possible with sufficient statistics available. Practically this means necessary continuous quality GPS signal receipt of no less 40-50 minutes long. This requirement meeting may grow into a serious problem. Possible solution may be making up some integral aircraft trajectory based upon joint analysis of GPS and IMU data (Lithopoulos, 1999). It is also no doubt that a major advantage of DTM production with laser locator is that its production is very technologically convenient. In such case DTM is a result of direct measurement having an original 3D nature. All the processes of technologic cycle are fully automatic, excluding therefore any subjective element. The latter circumstance has a decisive meaning, and it is directly followed by a possibility to ensure speed of processing and production of final DTM equal to aerial survey data collection. ♦ Informative capacity of DTM made by laser location appears much better. The most interesting is locator's ability to register more than one return per each scanning. So, the first return may refer to tree canopy, grass level, wires or towers of power line, as well as manmade facilities over the ground level. Return from true relief level will always be the last of returns. In its essence the laser locator image obtained upon aerial survey is a complex topologic matter that may be in the very first sight deemed a mix of DTM showing the true relief, and returns of other ground objects. A deeper approach allows, upon analysis of laser returns' spatial distribution, to get various specific features of scene topology. The most developed by the present time are the algorithms of automatic detection of power transmission lines for database creation and automatic designing (Medvedev, 1999). The works on laser locator data application in forestry topology are under way, algorithms of automatic detection of roads and railroads are developed. Obviously, the applications of automatic detection and positioning upon laser locator data will actively grow. However, from purely photogrammetric point of view, high informative capacity of laser locator data has its negative side as well, that is required DTM is not directly presented in the laser image. To separate it clearly, application of a number of sophisticated algorithms is needed, the current versions of which are not perfect yet. 2.2. Aerial photography Laser survey can be naturally integrated with digital photo survey. Indeed, digital cameras contrary to classic ones, are lighter, more compact and economic. Mounting thereof into an aircraft along with laser locator assumes no serious technical problem. GPS receiver included in any laser locator unit, may be as well used for registration of principal point coordinates, providing additionally full synchronization of laser and photo data. By the way, it may be mentioned that the idea of such integration is as well applicable to other digital remote sensing facilities like IR sensor, or multispectral scanner. However, the matter is not limited by only technological comfort. As it has been pointed, the integrated analysis of laser locator and digital photo data allows principally new final results. In addition to above, such integrated aerial survey is always provided with quite accurate data on camera's optical axis angular orientation, as the laser locator always utilizes such information for registration of

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