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capability for interactive visualization of GNSS
position tracks for each station, for the purpose of
enabling the identification of temporal relationships,
jumps or deviations from expected trends etc.
The RTKLIB (Takasu, 2013) suite is open
source software for standard and high-precision
positioning using observations from all currently
available GNSS satellite systems (GPS, GLONASS,
Galileo, BeiDou, QZSS). It was developed by T.
Takasu at Tokyo University of Marine Sciences and
Technology and has been available for free since
2006. The fact that RTKLIB code is accessible to
users, allows code modification and improvement,
meeting user’s needs. Since 2006, major
improvements have been made to the software
(latest version v.2.4.2), both by its developers and
RTKLIB users. RTKLIB consists of a portable
program library and several APs (application
programs) utilizing the library in order to facilitate
satellite data processing and determine the exact
station’s location. In addition, RTKLIB supports
several file formats, such as RINEX, RTCM,
NTRIP, ANTEX, and IONEX files. Also provides
limited capability to process and convert data, to
visualize the visibility (azimuths and elevations) and
the number of the used satellites against time, and to
export position results. This paper targets to deal
with RTKLIB's disadvantages by improving
RTKLIB's platforms for data acquisition and
visualization. One disadvantage is that RTKGET has
a complex procedure for data acquisition, causing
confusion in most of the users. RTKPLOT interface
doesn’t include statistics and metrics of computed
solutions. Furthermore, RTKLIB’s interface doesn’t
plot code and phase residuals.
4 THE GNSSGET AND
GNSSPLOT PLATFORMS
The newly developed GNSSGET and GNSSPLOT
platforms have been created with the aim to allow
the user, in a more transparent way, to communicate
with the RTKLIB software while retrieving data
from FTP Servers and performing user-selected
visualization tasks at the end of the data processing
stage. The technology and programming techniques
applied for the development of these platforms was
based mainly on MATLAB which provides the
ability to develop GUI applications through the
GUIDE (Graphical User Interface Development
Environment). GUIDE is a graphical environment
where a developer can build a GUI application, by
selecting various objects -included in the final
application- and by selectively adjusting various
application parameters related to the GUI. In that
way, certain properties of the user interface and
graphics components corresponding to a specific
user action can be associated with specific call-back
functions. This provides point-and-click control of
software applications, eliminating the need to learn a
language or type commands in order to run the
application. These platforms aren’t open source and
freely available to the users as they have been
developed with MATLAB 2008 version.
GNSSGET is essentially an Information
Communication Technology (ICT) platform which
acts like an umbrella, collecting information from
distributed data sources. Products vary, based on
parameters such as: time, space, file format,
Analysis Centers and product type. Various IGS-
coordinated Institutes and Data Centers provide
GNSS data via communication protocol FTP. The
objective of the application is to retrieve data from
isolated data sources and store them in the local
disk. This is accomplished by selecting few desired
parameters. The application functions are: storage of
GNSS observations and preview, retrieval of
broadcast and post-fit precise orbital data and
associated products and their storage on the local
hard disk. GNSS data and products, retrieved from
FTP Servers, are spatiotemporal big data, that is can
be in high volumes, and in compressed or
uncompressed form. Following the data collection,
GNSS data processing is carried out, by
communicating automatically the data to RTKLIB
and applying appropriate models and methods for
positioning and eventually generating position
solution results.
The next stage is the visualization of the results
which prompted us to build GNSSPLOT GUI.
Visualization includes time series diagrams,
statistics and metrics, plotting position history of
each GNSS station or georeferenced ground tracks
using Google Maps as background, Kalman filter
residuals and parameters as a function of time.
These two interfaces aim to direct the user,
minimizing errors from handling the available data.
In order to achieve this goal, these platforms provide
dynamic lists and warning messages to prevent the
user from frequent or common mistakes. The most
important functions are:
Gathering isolated GNSS data and products
via numerous FTP servers
Capability of local data storage and
decompression
Positioning error time series visualization