The Virtual Reference Station Concept in Finland – A Case Study

Survey Review ◽  
2007 ◽  
Vol 39 (304) ◽  
pp. 145-155 ◽  
Author(s):  
P. Häkli
Keyword(s):  
Reference Station ◽  
Virtual Reference

scholarly journals HEIGHT DETERMINATION TECHNIQUES FOR THE NEXT NATIONAL HEIGHT SYSTEM OF FINLAND - A CASE STUDY

2015 ◽  
Vol 41 (4) ◽  
pp. 145-155
Author(s):  
Timo Saari ◽  
Markku Poutanen ◽  
Veikko Saaranen ◽  
Harri Kaartinen ◽  
Antero Kukko ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Pilot Project ◽  
Satellite System ◽  
Reference Station ◽  
Virtual Reference ◽  
Precise Levelling ◽  
Height Determination ◽  
Weak Points ◽  
Global Navigation Satellite

Precise levelling is known for its accuracy and reliability in height determination, but the process itself is slow, laborious and expensive. We have started a project to study methods for height determination that could decrease the creation time of national height systems without losing the accuracy and reliability that is needed for them. In the pilot project described here, we study some of the alternative techniques with a pilot field test where we compared them with the precise levelling. The purpose of the test is not to evaluate the mutual superiority or suitability of the techniques, but to establish the background for a larger test and to find strong and weak points of each technique. The techniques chosen for this study were precise levelling, Mobile Laser Scanning (MLS) and Global Navigation Satellite System (GNSS) levelling, which included static Global Positioning System (GPS) and Virtual Reference Station (VRS) measurements. This research highlighted the differences of the studied techniques and gave insights about the framework and procedure for the later experiments. The research will continue in a larger scale, where the suitability of the techniques regarding the height systems is to be determined.

scholarly journals Investigation of accurate method in 3-D position using Cors-Net in Istanbul

2012 ◽  
Vol 18 (2) ◽  
pp. 171-184 ◽  
Author(s):  
Kutalmis Gumus ◽  
Cahit Tagi Celik ◽  
Halil Erkaya
Keyword(s):  
Real Time ◽  
Conventional Method ◽  
Global Positioning System ◽  
Complex Structure ◽  
Accurate Method ◽  
Reference Station ◽  
Positioning System ◽  
Virtual Reference ◽  
Global Positioning ◽  
Set Up

In this study, for Istanbul, there are two Cors Networks (Cors-TR, Iski Cors) providing Virtual Reference Station (VRS), and Flachen Korrektur Parameter (FKP), corrections to rover receiver for determining 3-D positions in real time by Global Positioning System (GPS). To determine which method (or technique) provides accurate method for position fixing, a test network consisting of 49 stations was set up in Yildiz Technical University Davudpasa Campus. The coordinates of the stations in the test network were determined by conventional geodetic, classical RTK, VRS and FKP methods serviced by both Cors-TR and Iski Cors. The results were compared to the coordinates by the conventional method by using total station. The results showed a complex structure as the accuracy differs from one component to another such as in horizontal coordinates, Y components by CorsTR_VRS and Cors_TR_ FKP showed 'best' results while the same technique provided X components consistent accuracy with the Y component but less accurate than by real time kinematic (RTK). In vertical components, of all the techniques used for the h components, CorsTR_VRS showed 'best' accuracy with three outliers.

Instruction through virtual reference: mapping the ACRL framework

2020 ◽  
Vol 48 (2) ◽  
pp. 243-257
Author(s):  
Rebecca Hill Renirie
Keyword(s):  
Design Methodology ◽  
Academic Librarians ◽  
Threshold Concepts ◽  
Virtual Reference ◽  
Content Type ◽  
Research Libraries ◽  
Instructional Content ◽  
Effective Use ◽  
Practical Implications

Purpose The purpose of this study is to examine teaching intent of information literacy threshold concepts via asynchronous reference transactions. Instructional content in academic librarians’ replies to research requests are analyzed for and mapped to threshold concepts contained in the Association of College and Research Libraries (ACRL) framework. Design/methodology/approach The author mapped the instructional content of a research request reply template to the content of the ACRL framework, then took a random sample of research requests using the template during the calendar year 2016. Additional instructional content provided in the sample replies was also mapped to the framework. Findings In providing written instruction for students to create searches from keywords and search subject-specific databases, every frame is at least partially addressed in the template except Scholarship as Conversation. However, individual librarians adapt the template to teach as needed and there are examples in this case study of teaching aspects of all six frames asynchronously. Practical implications This study provides support for librarians to teach the threshold concepts of the ACRL framework asynchronously at the point of need during virtual reference, and the effective use of a research reply template to accomplish this instruction. Originality/value Few recent studies examine instructional intent in asynchronous/email reference. This study examines teaching the ACRL framework via reference rather than instructional sessions. A portion of this research was presented as a poster at the 2017 ACRL Conference in Baltimore, Maryland.

scholarly journals Improving the Stochastic Model for VRS Network-Based GNSS Surveying

2019 ◽  
Vol 54 (1) ◽  
pp. 17-30 ◽  
Author(s):  
Thanate Jongrujinan ◽  
Chalermchon Satirapod
Keyword(s):  
Stochastic Model ◽  
Covariance Matrix ◽  
Ambiguity Resolution ◽  
Reference Station ◽  
Double Difference ◽  
Atmospheric Effects ◽  
Equal Weight ◽  
Virtual Reference ◽  
Positioning Accuracy ◽  
Variance Covariance Matrix

Abstract The VRS network-based technique has become the main precise GNSS surveying method especially for medium-range baselines (approximately 20-70 km). The key concept of this approach is to use the observables of multiple reference stations to generate the network correction in the form of a virtual reference station for mitigating distance-dependent errors including atmospheric effects and orbital uncertainty at the user’s location. Numerous GNSS data processing strategies have been adopted in the functional model in order to improve both the positioning accuracy and the success of ambiguity resolution. However, it is impossible to completely model the aforementioned errors. As a result, the unmodelled residuals still remain in the virtual reference station observables when the least squares estimation is employed. An alternative approach to deal with these residuals is to construct a more realistic stochastic model whereby the variance-covariance matrix is assumed to be homoscedastic. This research aims to investigate a suitable stochastic model used for the VRS technique. The rigorous statistical method, MINQUE has been applied to estimate the variance-covariance matrix of the double-difference observables for a virtual reference station to rover baseline determination. The findings of the comparison to the equal-weight model and the satellite elevation-based model indicated that the MINQUE procedure could enhance the positioning accuracy. In addition, the reliability of ambiguity resolution is also improved.

scholarly journals Geração de dados GPS de pseudodistância para uma estação virtual: métodos, implementação e análise dos resultados

2010 ◽  
Vol 37 (1) ◽  
pp. 03 ◽  
Author(s):  
Daniele Barroca Marra ALVES ◽  
João Francisco Galera MONICO
Keyword(s):  
Sao Paulo ◽  
Reference Station ◽  
São Paulo ◽  
Virtual Reference

O objetivo deste artigo é avaliar a qualidade das observáveis de pseudodistância geradas para uma estação de referência virtual (VRS - Virtual Reference Station). Para gerar os dados da VRS três métodos diferentes foram implementados e testados. No primeiro método, foram empregados os dados brutos das estações de referência da rede. O segundo foi baseado nas correções de duplas diferenças das estações de referência. No terceiro método, foram utilizados modelos atmosféricos (ionosfera e troposfera) para gerar os dados da VRS. As estações da rede do estado de São Paulo foram utilizadas para realizar os experimentos. A VRS foi gerada na posição de uma estação de referência (arquivo real), com coordenadas conhecidas. Para avaliação, os dados da VRS foram comparados com aqueles provindos do arquivo real. Os resultados obtidos foram similares, proporcionando acurácia decimétrica ou centimétrica, dependendo do método.

scholarly journals Posicionamento GNSS em Tempo Real: Evolução, Aplicações Práticas e Perspectivas para o Futuro

2020 ◽  
Vol 72 ◽  
pp. 1359-1379
Author(s):  
Claudia Pereira Krueger ◽  
Paulo Sérgio de Oliveira Junior ◽  
Silvio Jacks dos Anjos Garnés ◽  
Daniele Barroca Marra Alves ◽  
Jorge Felipe Euriques
Keyword(s):  
Real Time ◽  
Global Positioning System ◽  
Precise Point Positioning ◽  
Reference Station ◽  
Space Representation ◽  
Positioning System ◽  
Differential Gps ◽  
Virtual Reference ◽  
State Space Representation ◽  
Global Positioning

O posicionamento em tempo real por meio do emprego dos sinais de satélites foi um avanço nas navegações aérea, marítima e terrestre com o surgimento do GPS (Global Positioning System). Contudo as precisões horizontais e verticais de 100 m e 150 m (nível de probabilidade de 95%) alcançadas, estando a SA (Selective Availability) ativada, passaram a não ser satisfatórias para muitas aplicações e os usuários buscaram galgar outros níveis de precisões. Esforços foram investidos no chamado posicionamento diferencial DGPS (Differential GPS), o qual possibilitou obter precisões em torno de dez vezes melhores do que as do posicionamento absoluto.  Posteriormente, usando-se a fase da onda portadora, conseguiu-se realizar posicionamento com maior acurácia por meio do método RTK (Real Time Kinematic), atingindo qualidade centimétrica. Na sequência, houve uma evolução para posicionamentos em rede, empregando, por exemplo, o algoritmo de VRS (Virtual Reference Station). Vários erros nas observáveis dos satélites passaram a ser modelados com uma solução de multiestações em tempo real. A partir de 2012, surgiram serviços e produtos que favoreceram o desenvolvimento do RT-PPP (Real-Time Precise Point Positioning) baseado no conceito SSR (State Space Representation). A busca da solução das ambiguidades no RT-PPP deu origem ao PPP-RTK com menor tempo de fixação das ambiguidades e convergência para a solução acurada do posicionamento. Neste artigo apresenta-se como foi a evolução do posicionamento em tempo real, algumas das aplicações no âmbito nacional e as perspectivas  desta modalidade de posicionamento para o futuro.

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