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:: HIGHWAY SURVEYING WITH DGPS BASED ON RTCM SATELLITE CORRECTIONS. S. COSSI, M. MARSELLA, C. NARDINOCCHI, L. TOMBOLINI

Document type:: Monograph

Structure type:: Chapter

component. The autonomous accuracy is about 100 meters (2dRMS). These accuracy specifications apply with Selective Availability active and when at least 5 satellites are visible, PDOP is less than 6, good signal to noise ratio and the satellite elevation mask is set at 15 degrees. Accuracy specification may change if Selective Availability is deactivated or modified. The receiver is capable of receiving RTCM SC-104 standard format broadcast from a Trimble reference station or from a provider, like OMNISTAR. Ionospheric conditions, multipath signals or obstructions of the sky by buildings or heavy tree canopy may degrade accuracy by interfering with signal reception. Optimal accuracy is obtained by collecting data in an environment that is devoid of large reflective surfaces and also has a clear view of the sky, as happen along a highway. The main advantage of implementing with GPS existing road survey systems is the integrability (Greenspan, 1996) with the sensors mounted on board, which usually includes an odometer. In such cases, the integration allows for establishing a rigorous correspondence between the relative mile chainage measured by the odometer and the absolute GPS co-ordinates. Furthermore, the odometer guarantees the continuity of the positioning when interruptions in the GPS signals occur. 2.1 Differential GPS The differential GPS technique is based on two receivers operating simultaneously: the one located in a known position is called REFERENCE or MASTER STATION, and the second one located in the unknown position. If the last one is moving, it is called NAVIGATOR o ROVER and the technique is named DGPS kinematic. DGPS kinematic method is based on the measurements of the length of every segment joining the MASTER and the ROVER stations; moreover the angle that such segment forms with the North of the reference system and the slope of the segment are also measured. Therefore the co ordinates of the ROVER station are known relatively to the fixed MASTER position. It should be noted that the achievable accuracy depends on the type of GPS observables (phase or code) which can be acquired by the adopted receivers and on the inter-distance between the stations (Seeber et al. 1995). 2.2 Real Time Kinematic Differential GPS In case of the two receivers being joined trough a radio link or mobile phone communications, the position of the ROVER can be determined in real time (Real Time Kinematic). The raw data of the stations are immediately elaborated from a software installed in one of the two receivers (generally in the MASTER) and the corrected position is sent to the other one (ROVER) with a maximum delay of a second. Since the radio connection use an assigned low frequency band to avoided interruptions in the transmission of the corrected data it is necessary to maintain the distance between the two stations within lCP-20km. In this way the relative accuracy of the RTK technique is really high (1 O' 5 10' 6 ) and do not require any further post-processing of the data. 2.3 Post Processing Differential GPS Alternatively, a post-processing differential procedure can be applied to the raw data downloaded from the memory of the two receivers. The post processing solution is not strongly limited by the distance between the two receivers and provides co-ordinates of high accuracy ( 1 O' 6 10‘ 7 ) (Scwharz et al., 1989). Since most of the highway surveying requires an accuracy requirements are within 1 2 meters, both DGPS techniques can be adopted even though for different applications. The RTK method is a fast procedure only suitable for small range survey owing to the limitation of communication link. The PP method is more time consuming but it can be applied for positioning ROVER receivers at a distance of about 100km. This technique can be applied over the entire national highway network, provided that an optimised reference station network is established. The co-ordinates of the vertices of the network have to be previously determined. A limited number of MASTER receivers can be moved in the specific area of interest. As an example, a network covering the highway managed by the Società Autostrade was designed and shown in Figure 1, where the centres of the circles correspond to the GPS station locations. Figure 1 GPS Reference Station Network configuration that covers the highway system managed by the Societa Autostrade 2.4 RTCM-104 Differential GPS

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