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:: RTK SURVEY USING COMBINED GPS+GLONASS L1/L2 CARRIER PHASES. Crocetto N. - Gatti M. - Marchesini M. - Negroni F. - Russo P.

Document type:: Monograph

Structure type:: Chapter

42 particularly difficult for the reception of the GPS signal (Fig. 11). Fig. 11. Measurement of a point with the GPS+GLONASS RTK technique. The tunnel is about 2 km long and its course is rather tortuous, both in planimetry and in altimetry. In fact, we measured differences in height between successive vertices only a few hundred meters apart of up to 18 meters. A preliminary marking out performed to obtain information for the realisation of the working plan was followed by a rigorous measurement of the vertices of the polygon. A planimetric precision of 2 cm and an altimetric precision of 3 cm was required for this measurement \ The survey was performed with a mixed technique, GPS+GLONASS and traditional. The satellite technique was used in the static and fast static mode. The planimetric orientation of the GPS+GLONASS survey was carried out with some trigonometric vertices of the first order network and a vertex of the IGM95 GPS first network. For calculation of the orthometric heights of the tunnel’s course, we performed an altimetric link, by trigonometric levelling, of some datum points in the area. During construction of the tunnel, after the surveys had been performed, we proceeded to control the excavation operations. This was carried out by sampling some 3 These precisions are required whenever the excavation operations in a tunnel are performed with an in-line tunnelling machine. vertices of the polygon, selected on the basis of their position along the course (start of tunnel, end of tunnel and where the conduit intersected various constructions and existing works: a railway link, a cave, a hospital, etc.). The control was performed with the traditional topographical technique and the GPS+GLONASS RTK technique; the established precisions were close to those indicated in the measurement of the vertices. The RTK survey was carried out with the same instrumentation described in section 1. The radio link connection was realised with a Satel AS2X with selectable frequency and directional antenna; this apparatus permits larger ranges than the conventional ones and thus is particularly suitable in the presence of vegetation. The threshold filters for the fixes were selected at 4 cm for planimetry and 3 cm for altimetry. The acquisition interval was set at 1" and the cut off at 5°. The measurement session lasted one hour. For the co-ordinate transformations, we used the parameters calculated during the static GPS+GLONASS survey. Despite the difficult operating conditions, there were always 5 satellites visible, with a PDOP never greater than 3. The cycle losses were frequent, but the apparatus was always re-initialised in the minimum possible time. The traditional survey was performed with a NIKON DTM850 integrated station. Table 2 summarises the mean values (and range) of the absolute differences between the co-ordinates of the sample points measured with the GPS+GLONASS RTK instrumentation and the co-ordinates of the same points measured with the traditional instrumentation. Differences in the Mean value Range co-ordinates (cm) (cm) 5N 3.5 9.0 ÔE 2.5 5.0 8H 2.0 3.0 Table 2. Differences in the co-ordinates measured with the RTK technique and with the integrated theodolite. The results of this test revealed the following aspects: • the acquisition capacity of the GPS+GLONASS RTK system even in the presence of vegetation and obstacles to signal reception; • minimum times of re-initialisation; • the possibility of operating with a fix filter that is very low in relation to the operating conditions; • precisions of positioning comparable to those obtained with traditional topographical instrumentation. CONCLUSIONS The availability on the market of GPS+GLONASS receivers on the L1-L2 frequency has led to appreciable advantages in operational geodesy. In this paper, we have

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