Application SKPOS network solution quality monitoring

According to the act NR SR num. 215/1995 Z. z., part (2), §4, Geodetic and Cartographic Institute Bratislava (GKÚ) is committed to providing quality and modern services for all GNSS equipped users for all works within the national geodetic reference systems. This task is implemented by the Slovakian spatial observation service (SKPOS) which represents active geodetic controls in Slovakia ie national implementation of the European terrestrial reference system 1989 (ETRS89). Following this information it is very important to constantly monitor the quality of the provided SKPOS network solution beside the SKPOS control software monitoring tool, which is the task of the created application.

Creation of the SKPOS network quality monitoring application follows the basic service provider requirements which were:

Monitoring has to be done constantly,
Monitoring has to be done in the all Slovakia,
Monitoring has to be done automatically,
Results from the monitoring have to be available to the users.

Finding a non-expensive solution without the need to build real monitor stations or buying expensive software was also considered during defining the application.

1 Principle of the application

The SKPOS network solution quality monitoring is based on a virtual principle. The core of the monitoring is carried out by the RTKNAVI software, the part of the RTKLIB software package (RTKLIB web, 2013). RTKNAVI, functioning as SKPOS VRS station, simulates the real rover measurement in terrain and processes the baseline between this simulated rover and the nearest SKPOS permanent station. The resulting criteria, or quality criteria, are then represented as differences between the computed position of the SKPOS permanent station from the determined baseline and the reference SKPOS permanent station coordinates. Remark: Data from the permanent stations of the neighbouring positioning services enters into generation of SKPOS network solution (for more information see the map of the reference stations available on www.skpos.gku.sk), but monitoring of theirs surroundings are not active due to technical reason.

2 Monitored positions and the testing areas

Territory of the Slovakia is divided into circular areas with the origins directly in the SKPOS permanent stations (Fig.1). Monitored positions are distributed in directions 2km, 11km, 20km from the permanent station within each testing area. The azimuth of the testing baselines reaches 0°, 45°, 90°, ..., 315° values. The 15° azimuth interval in combination with three directions are used intentionally to ensure the achievement of 24 testing positions within one day and one testing area. The azimuth/direction combination within one hour per testing area is chosen randomly i.e. never repeats itself within the same day and area. The selection of the testing areas within one hour is set randomly as well. The presented settings were chosen to ensure the elimination of the systematic effects and to avoid or minimise the problem with the data correlation on time.

Fig. 1 Testing areas.

The length of one testing (one position baseline processing) lasts 120 epochs (2 minutes). This time represents the required time period for the determination of elementary surveying points set by the Decree of Geodetic, cartographic and cadastre authority of the Slovak republic num. 75/2011 (ÚGKK SR, 2011). All together 720 testing measurements are performed with the application within one day (Fig.2).

Fig. 2 Monitored positions within one day.

The coordinates of the monitored positions are entered into application in the latitude, longitude and physical height format (φλH). The physical height H is achieved from the digital height model SRTM (Shuttle Radar Topography Mission). This kind of height was selected to ensure better simulation of the rover measurement in the terrain.

3 Statistical processing and the result depiction

Few sets of the ellipsoidal coordinates φλh and the information about baseline processing quality (fix, float atc.) are the results of the baseline (rover VRS – SKPOS permanent station) processing in RTKNAVI software. At first all nonfix solutions are eliminated from the saved sets of coordinates. Then Grubbs test on the α = 0,05 significance level is used for eliminating outlying values. From the remaining values the average ellipsoidal coordinates are computed and transformed onto the local topocentric coordinate system (neu) with the origin in the SKPOS permanent station. Finally the computed deviations for horizontal (ne) and vertical (u) component are graphically depicted into charts (Fig.3).

Definition of the horizontal deviation is as follows:

(1)

Definition of the vertical deviation is as follows:

(2)

The horizontal lines on the figure (Fig.3) represent the daily quadratic averages (Root mean square) for horizontal (RMS_ne) and height component (RMS_u)

(3)

where:

x_i - represents horizontal ne and vertical deviations u

n - number of values.

Fig. 3 Example of the graphical representation of the horizontal and vertical deviations.

More information about the application can be found also in Karol Smolík diploma thesis, see (Smolik, 2013).

References

RTKLIB web, 2013: RTKLIB open software web page. [online]. [cit. 5.5.2013]. Available on: http://www.rtklib.com.

SMOLÍK, K. 2013: SKPOS network solution quality monitoring in real time. Diploma thesis. Bratislava: Faculty of civil engineering, Slovak university of technology in Bratislava, 2013. 53 pages. (in Slovak). Available on: http://crzp.sk/crzpopacxe?fn=*recview&uid=1281939 .

ÚGKK SR, 2011: Geodetic, cartographic and cadastre authority of the Slovak republic Decree num. 75/2011.