Bulletin of the GSI (Vol.67)
Development of Multipath Mitigation Methods to Improve GNSS Positioning Accuracy Under Urban Environments
FUKUZAKI Yoshihiro, ONAKA Yasuhiko, TADA Naohiro, MIYAGAWA Kohei, SAKAI Kazuki, FURUYA Tomoaki, KAMAKARI Yuki, YAMAO Hiromi, HIYAMA Yohei and HATANAKA Yuki
The accuracy of Global Navigation Satellite System (GNSS) positioning is easily degraded under severe environments such as urban street surroundings due to the blockage of satellite signals by tall buildings. One of the causes of GNSS positioning accuracy degradation is the multipath effect, a phenomenon known to occur in urban areas. To improve the positioning accuracy under such environments, we developed three new methods for multipath mitigation by employing promising techniques from previous studies. The first is the application of an elevation cutoff mask model produced from the distribution data of area obstacles causing the blockage of GNSS signals. The distribution at each site is identified from photos of an overhead sky (e.g. fisheye lens photos), and the elevation cutoff mask model for each site is individually produced and applied to eliminate non-line-of-sight satellites. The second is the application of another elevation cutoff mask model produced from the distribution data of buildings identified from a 3D map. The third is a quality check of the observation data utilizing L1 and L2 Doppler observables. If the observation data contain undesirable signals such as multipath signals, the difference between the L1 and L2 Doppler observables will not agree with the difference in the case of only true signals. By using the discrepancy detected with the Doppler observables, the data can be rejected as invalid observations. These three methods allow observers to select the proper satellites with greater certainty and perform more accurate positioning by identifying the observation data to be rejected. This paper presents the development results of the new methods.
The United Nations Vector Tile Toolkit (UNVT) is an open source software project established under Working Group 4 (WG-4) of the United Nations Open GIS Initiative in 2018 with an objective to enable the use of open source vector tile technologies within the United Nations operations and also within the United Nations member states among other applications. To incubate UNVT, the project is being developed in the following three directions. (1) In order to establish a sustainable software development community, the project has a good momentum to apply for the Open Source Geospatial Foundation (OSGeo) incubation process guided by the principle to leave no one behind. (2) Through its Running Code, UNVT makes unique contribution to the global agendas under the United Nations Committee of Experts on the Global Geospatial Information Management (UN-GGIM). (3) In order to minimize the work duplication and maximize the shared experience, the UNVT team demonstrates the implementation of vector tiles and then the project participants apply the service in practice. Following the resolution in the Preamble of the Charter of the United Nations, UNVT is trying to combine the efforts of the peoples of the United Nations to address global issues using the latest vector tile technology that enables the dissemination of any vector geospatial information efficiently and independently.
SUGA Masaki, NUMATA Yoshinori and NAKAMINAMI Kiyoaki
The Geospatial Information Authority of Japan (GSI) defined the “Notation Rules of Geographical Names, etc. in English” and compiled geographical names and other data in English notation based on these Rules in 29 March 2016 for multilingual notation of geospatial information. In March 2019, GSI released on a trial basis a web map (“map in English notation”) using annotation vector tiles in which data in English notations are stored. Then, GSI configured a program for automatically converting annotations in different languages (French, Korean, simplified Chinese, traditional Chinese and Romanized Japanese) and displaying the results on the web browser. Finally, GSI published in 14 February 2020 a web map named “Japan Map in Multilingual Notation” implementing the program on a trial basis. This report describes our approach until the experimental release of the multilingual maps.