GEODETIC INVENTORY OF A COOLING TOWER USING REFLECTORLESS TECHNIQUE

Marek Woźniak

Warsaw University of Technology

ABSTRACT

The technique of reflectorless measurements finds more and more applications in geodetic practice. Its new stage is video-tacheometry. It is quite a new measurement technology combining tacheometric measurements and digital photogrammetry. On the one hand, it ensures perfect metricity of a set of spatial points (XYZ), on the other, it offers “continuous” image representation of an object surface. The combination of these data into a uniform measuring system and the ensuing result processing allow us to obtain unprecedented effects. This article presents inventory measurements of the surface of a cooling tower taken with a precise Leica TCRP 1201+ tacheometer and a TOPCON Image Station 03 video-tacheometer. Video-tacheometric measurements were carried out in the SCAN AREA and LINE modes. The obtained results were confronted with the design values of the cooling tower and accuracy measurements taken with a TCRP1201+ measuring system. The results of the research allow us to see all the flaws and merits of the new technology and make its accuracy assessment.

1. INTRODUCTION

Thin engineering structures require special care to ensure that their stability is appropriate and by the same token their safety. Engineering structures of this type are cooling towers. The study of static stability of these structures requires precise recognition of their real shape in relation to the design surface. The size of these structures and a large number of points required to represent the structure as well as difficult access to survey points have always been a major problem for surveyors. Various methods and technologies have been used earlier to carry out these measurements. They have been mainly based on the construction of angular intersections to control points. It has also been required to signal measurement points. The surveying has been exceptionally arduous and the point representation of a structure limited, due to these difficulties. Some hope was raised by the introduction of photogrammetric methods. Photogrammetric techniques ensured the required density of area ”sampling” but obtained accuracies were limited and often inadequate. After the introduction of electronic theodolites and laser eyepieces, it was possible to meet accuracy requirements as well as those concerning information density about a particular structure. The above technology called Remote Measuring System (RMS) involved very precise field measurements, demanding intense concentration on the part

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– 518 –

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– 520 –

In the present case, the adjustment was made by the approximation method of least squares only of the points of the lowest part of the cooling tower, assuming that the direction of the vertical (the z-axis) was to be maintained. Such an approach is required for the right assessment of the structure stability. The standard form of measurement data processing by using TCRP observations, in the AutoCAD system is illustrated in Fig. 6.

Fig. 6. Typical report drawings with deviations from the design made in AutoCAD.

Video-tacheometric technology provides us with a much greater number of data and the structure model obtained therein can be the basis for creating any sections and profiles required, as well as any contours of the model surface (Fig.7). Additionally, digital photos of the structure are noted, which can be used for texturing the model.

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– 521 –

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– 522 –

everal timeto assess threment resuntal measurs not only twork, but .

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CONCLUD

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MARKS

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– 523 –

nges in suctarget ident

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reatment tof these stranced survoften very pes do not

face of the s, due to th

ccessive retification.

e surface devi

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– 524 –

particularly visible in the case of a complicated surface of the structure or a partially obscured measurement beam. That is when different disturbances occur, which are difficult eliminate, undermining the accuracy effect obtained. Reflectorless surveying technologies used in modern tacheometers are not devoid of synchronization errors in time-space observations of directions and distances. This element becomes exceptionally prominent during measurements in the scanning mode. The introduction of video-tacheometric technology supplements geodetic observations still by another element, which is a digital image. In this case, it is possible to use the analysis of this image as support in making detailed measurements. This technology, apart from making observations, contains a complete method for processing these observation results in an automatic way. It speeds up considerably the final outcome of the study, eliminating mistakes in combining observations, and enables to conduct fast the successive stages of data processing. The constructed virtual model of the structure can be the subject of an indefinite number of analytical -graphic transformations. New forms of graphic presentation enable better perception of the final outcome of the studies and, due to automatic data processing, make these studies more objective and reliable. REFERENCES W. Krzyżanowski, R. Malarski, M. Woźniak, A. Wróbel "Komunikat z pomiarów

odkształceń kominów przemysłowych metodami geodezyjnymi" Materiały konferencji naukowo-technicznej nt. METODY GEODEZYJNE W PROCE-SACH STEROWANIA ANTROPOPRESYJNYCH ZMIAN ŚRODOWISKA Sobótka k/Wrocławia 14-16 10 1993 r.

M. Woźniak Monitoring of construction shape changes using reflectorless techniques - Reports on Geodesy – Politechnika Warszawska, Instytut Geodezji Wyższej i Astronomii Geodezyjnej - No. 1(84) 2008.