Tukka, A. A., Dodo, J. D. and Ariyo, T. O.
, JMAS Vol 4 Issue 1 2016
The Journal of MacroTrends in
Applied Science
MACROJOURNALS
COMPARATIVE ANALYSIS OF POSITIONAL RESULTS
OF POST PROCESSED GPS SURVEY DATA USING
THREE TRIMBLE SOFTWARE PACKAGES
Tukka, A. A.*, Dodo, J. D.** and Ariyo, T. O.*
*Department of Surveying and Geoinformatics, Federal University of Technology, Akure, Nigeria.
**Center for Geodesy and Geodynamics, Toro, Nigeria
Abstract
In Global Positioning System (GPS) survey, post processing technique has proved to be
the most efficient means of obtaining precise and accurate positional results. Different
types of post-processing software are available and surveyors use them at random
without knowing their comparative efficacy. Trimble software packages can be used
to post process GPS data in order to determine final positions of points on earth’s
surface. However, these packages have not been compared to determine which of the
software is better than the others under certain circumstances. Therefore, this study
attempts to assess and compare positional results of points obtained using Trimble
Business Centre (TBC), Trimble Total Control (TTC) and Trimble Geomatics Office (TGO)
software for post processing GPS survey data of the same study area. The survey data
was processed at 150, 250 and 350 satellite elevation angle using 24 hours GPS (at 30
seconds interval) RINEX data of four stations. These are FUTY Continuously Operating
Reference System (FUTY CORS), DDD1, DDD2 and DDD3 stations for GPS week 1622
and Day 40. The results obtained revealed that TBC has the least Root Mean Square
Errors (RMSE) and Trace of variance-covariance matrix in the baseline domain. Also, in
the coordinate domain, TBC gave the least value of coordinate variance. TGO
produced the highest values of RMSE and Trace of variance-covariance matrix in the
baseline domain and also the highest variance in coordinate domain. Therefore, TBC
was found to give more consistent and satisfactory positional results than TGO and
TTC. Hence, TBC is recommended, as the most appropriate commercial software for
post processing GPS surveying data.
Keywords: Comparative Analysis, Positional Accuracy, GPS Survey Data, CORS, TGO, TTC and TBC
packages
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
1. Introduction
In surveying, the need to obtain spatial positions of both natural and man-made features arises
from time to time and this has been the reason for all observations in surveying and mapping.
Until now, large errors associated with geodetic networks had been posing serious challenges
within the Surveying and Mapping industry as only approximate solutions were frequently used
to define positions of points. Nowadays, however, the advent of GPS with different post
processing software packages designed with sophisticated scientific and vendor based
algorithms for the acquisition and processing of data, errors that formerly poised threat on the
integrity of position determination in surveying solutions can be modeled and significantly
minimized or eliminated using the appropriate GPS procedure depending on the required
accuracy. It has been stated, from the review of related literature, that there are scientific based
and commercial based software packages for the post-processing of GPS data. The scientific
based packages include Bernese and GAMIT software while few of the commercial based
packages are GPsurvey, SKI-Pro and Trimble software. Many commercial software packages for
post-processing GPS survey data have been rolled out to the market and personnel within
surveying industry rush out to purchase any kind of software package without taking into
consideration the efficacy or level of reliability of the software that best suits the type of task to
be executed. This, sometimes, result to disappointments as the final results obtained from the
use of such software fail to meet the desired accuracy specification thereby leading to loss of
man-hour and resources. Trimble software packages are useful tools for post processing GPS
surveying data to determine positions of points on the surface of the earth (TGO, 2004). In the
work of Ojigi (2008), scientific based Bernese software was compared with TGO commercial
based package and the conclusion showed that the scientific based software produced better
results. However, consideration has not been given to the possibility of achieving good results
from other Trimble packages such as TTC and TBC. Also, comparison of the three Trimble
packages has not been carried out to determine which of these packages can process GPS data
better than the others under certain circumstances. Therefore, it is the objective of this paper to
carry out comparative analysis of positional results of post-processed GPS survey data using
Trimble Business Centre (TBC), Trimble Total Control (TTC) and Trimble Geomatics Office (TGO)
software packages.
2. Scope of the study
The scope of this study is limited to the acquisition of 24 hours GPS data at 30 seconds interval
on FUTY CORS station and three other stations which include DDD1, DDD2, and DDD3 stations.
The collected data were post processed using TBC, TTC and TGO software at 150, 250, and 350
satellite elevation angles to determine baselines and coordinates of these stations. The results
obtained were analyzed and compared leading to drawing appropriate conclusions.
3. Study Area
The study area is Adamawa State of Nigeria as shown in figure 1 while figure 2 shows the study
site which includes the GPS observation stations used within the study area. These stations are
FUTY CORS station at the Modibbo Adama University of Technology of Yola in Giere Local
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Governmenr Area (LGA), DDD1 stations is located on Ugurore hill in Numan LGA, DDD2 station is
located in Guyuk LGA and DDD3 is located in Ganye LGA.
Figure.1: Map of Nigeria showing Adamawa State in blue color (Dodo et al. 2011)
Figure 2: GPS observation stations within Adamawa State (Dodo et al, 2011)
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
4. Methodology
The general approach used in the methodology is limited to the acquisition of 24 hours GPS data
at 30 seconds interval on FUTY CORS (as control station) and three other stations which include
DDD1, DDD2, and DDD3 stations. The collected data were post processed using TBC, TTC and
TGO software at 150, 250, and 350 satellite elevation angles to determine baselines and
coordinates of the stations. The results obtained were analyzed and compared to draw
appropriate conclusions. .
5. Data
The data acquired for the study are GPS (Promark 3) observed data, satellite orbit data. The GPS
data, also known as Receiver Proprietary data are mostly in compact form which is later
converted into observational format usually referred to as RINEX data. The satellite orbit data
are obtained from the precise satellite orbit files from the International GNSS Service (IGS)
website in SP3 format (Leick, 1993 and Leick, 1994). This was obtained for GPS Week 1622 and
Day 40.
Data Quality
The quality of data used for any experiment can be determined by the validity and reliability of
such data based on the assumption that the observer of such data are trustworthy and
experienced. The validity of the data is measured by the precision of the instrument used and
hence the precision of the measured sets of data. In real time mode, the GPS equipment was
initially used to determine the coordinates of a control point (DDD1) repeatedly and the results
obtained were found to be closely clustered. This gave an assurance that the data obtained are
of high precision. The reliability of data is determined by the accuracy of the data. That is, the
degree of closeness of the sets of data to another sets regarded as the true values, often
referred to as ‘Gold Standard Data’ (Roos et. al., 1982 and Roos et. al., 1989).
The mean value of the initial set of coordinates obtained for DDD1 was compared with the
known values and the result showed insignificant differences. This further gave an assurance
that the data acquired with the GPS are reliable. Hence, based on the above report, it can be
inferred that the validity, reliability and hence the quality of the data used in this study are
satisfactory.
Data Processing
The GPS data acquisition mode, the software used, the selected processing parameters and
settings used are shown in Table 1.
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Table 1: Post processing parameters and settings used
Trimble Business Center(TBC)
Software Used Trimble Total Control(TTC)
Trimble Geomatics Office(TGO)
Data Acquisition Mode Static Mode
Data processing Mode Static mode at 30 seconds interval processing
Tropospheric Model used Hopfield Model
Satellite orbit ephemeris used Precise Orbit (IGS)
Satellite elevations used 150, 250 and 350
Solution type Ionospheric-free Double Difference Fixed
6. Presentation of Results
The detailed post-processed results obtained using Trimble Business Center (TBC), Trimble Total
Control (TTC) and Trimble Geomatic Office (TGO) software are hereby presented. In the baseline
domain, the baseline lengths and their respective Root-Mean-Square-Error (RMSE) values are
shown in Table 2 while the traces of variance-covariance matrices associated with each baseline
are shown in Table 3.
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Table 2: Computed baselines obtained for different software
SATELLITE ELEVATION ANGLES
150 250 350
Adjusted RMS Adjusted RMS Adjusted RMS
Baseline(s) Softwar Baseline (mm) Baseline (m) (mm) Baseline (mm)
e (m) (m)
TGO 29613.819 0.035 29613.827 0.037 29613.828 0.037
TTC 29613.814 0.021 29613.814 0.019 29613.813 0.018
FUTY-DDD1 TBC 29613.818 0.012 29613.818 0.002 29613.818 0.002
TGO 86776.655 0.005 86776.653 0.005 86776.654 0.005
TTC 86776.659 0.004 86776.659 0.007 86776.658 0.006
FUTY-DDD2 TBC 86776.660 0.001 86776.660 0.001 86776.660 0.011
TGO 121458.417 0.005 121458.423 0.005 121458.421 0.004
TTC 121458.417 0.007 121458.417 0.007 121458.416 0.006
FUTY-DDD3 TBC 121458.420 0.001 121458.420 0.001 121458.420 0.011
TGO 90515.585 0.008 90515.591 0.007 90515.591 0.007
TTC 90515.580 0.009 90515.580 0.009 90515.581 0.008
DDD2-
TBC 90515.584 0.004 90515.584 0.001 90515.584 0.014
DDD1
TGO 103599.997 0.038 103599.992 0.026 103599.991 0.005
TTC 103600.003 0.010 103600.003 0.010 103600.002 0.008
DDD1-
TBC 103600.003 0.005 103600.003 0.005 103600.003 0.015
DDD3
TGO 192651.973 0.065 192651.975 0.054 192651.974 0.044
TTC 192651.973 0.046 192651.973 0.026 192651.973 0.016
DDD2-
TBC 192651.976 0.010 192651.976 0.009 192651.976 0.001
DDD3
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Table 3: Traces extracted from variance-covariance matrices from baseline computation
Satellite Elevation Angles
150 250 350
Baselines Software TRACE TRACE TRACE
TBC 0.000112795 0.000112795 0.000112795
FUTY-DDD1 TTC 0.0003107264 0.0003107264 0.0004871624
TGO 0.0004912595 0.0005779944 0.0005911955
TBC 0.0001235909 0.0001010893 0.0001235353
FUTY-DDD2 TTC 0.0003370913 0.0003370913 0.0005953012
TGO 0.0006110819 0.0008149198 0.0008590802
TBC 0.0002619487 0.0002619487 0.0002619487
FUTY-DDD3 TTC 0.000681351 0.000681351 0.0013573371
TGO 0.0012816345 0.0022644377 0.0025980843
TBC 0.0001624165 0.0001496374 0.0001496374
DDD2-DDD1 TTC 0.0004248273 0.0004248273 0.0007162672
TGO 0.00012699241 0.0008913377 0.0009133501
TBC 0.0002462816 0.0002462816 0.0002462816
DDD1-DDD3 TTC 0.000608043 0.0002462816 0.0011652118
TGO 0.0012299888 0.0020869762 0.0022558039
TBC 0.0002701576 0.0002701576 0.0002701576
DDD2-DDD3 TTC 0.0007434803 0.0007434803 0.0013975016
TGO 0.0012008911 0.0020615067 0.0027999388
The grid coordinates of each station and the variances associated with their coordinates at 15 0,
250 and 350 satellite elevation angles are presented in tables 4, 5 and 6 respectively.
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Table 4: Grid coordinates and variances at 150 satellite elevation angle
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Table 5: Grid coordinates and variances at 250 satellite elevation angle
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
Table 6: Grid coordinates and variances at 350 satellite elevation angle
7. Analysis of results
Analysis of the results obtained from the post-processing, at 150, 250 and 350 satellite elevation
angles, is separately carried out based on baseline and coordinate domains. In the baseline
domain, the parameters considered for analysis are RMSE and Traces for the shortest and
longest baselines. From table 2, it can be observed in columns 3, 5 and 7 that TBC has the least
RMSE values of 0.012m, 0.002m and 0.002m for the shortest baseline (FUTY- DDD1), at 150, 250
and 350 satellite elevation angles respectively, TGO has the highest values of 0.035m, 0.037m
and 0.037m while TTC produced values of 0.021m, 0.019m and 0.019m at the same satellite
elevation angles. In addition, for the longest baseline (DDD2 – DDD3), it can be observed that
TGO has the highest RMSE values of 0.065m, 0.054m and 0.044m, TTC produced values of
0.046m, 0.026m and 0.016m while TBC recorded values of 0.010m, 0.009m and 0.001m.
Moreover, it can be observed that there seems to be a general decrease in the RMSE value as
satellite elevation angle increases.
Furthermore, traces of the variance-covariance matrices were used to analyze the results
obtained from TBC, TTC and TGO software at 150, 250 and 350 satellite elevation angles. The
trace of a matrix is the sum of its diagonal elements. Feddeerov (1972) had suggested the use of
trace of variance-covariance matrix for choosing the best estimates of computed parameters.
Also, Idowu (2007) used the traces of covariance matrix to determine the best approach to the
observation equations method of least square adjustment for survey network.
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Tukka, A. A., Dodo, J. D. and Ariyo, T. O., JMAS Vol 4 Issue 1 2016
The results shown in table 3 indicate that TBC generally produced smaller traces than TTC and
TGO software packages. Therefore, based on the above, it can be inferred that the TBC software
produced better baseline results than TTC and TGO software packages. In the coordinate
domain, variances associated with the computed grid coordinates of DDD1, DDD2 and DDD3 are
analyzed. Table 4 contains the coordinates obtained at 150 satellite elevation angle. The least
variance of 0.000004m was produced by TBC software on stations DDD1 and DDD2 for the
northing coordinate while the highest variance value of 0.000841m was produced by TGO
software on stations DDD1 and DDD3 for the height coordinate. Also, table 5 contains the
coordinates obtained at 250 satellite elevation angle. From the results, it is observed that TGO
software produced the largest value of variance on DDD3 station for the height coordinate while
TBC produced the least variance for DDD1 and DDD2 stations. Table 6 contains results at 350
satellite elevation angle. These show that TGO and TTC produced highest variances on DDD2
and DDD3 for the height coordinates while TBC gave the least variance for the northing
coordinates. Based on the above analysis, it can noted that the use of TBC software for post-
processing GPS data has consistently produced the smaller values of variance in both horizontal
and height coordinates than TTC and TGO software packages. Hence, it can be stated that
better positional results are obtainable from the use of TBC software for post-processing GPS
data than TTC and TGO packages.
8. Conclusion and Recommendations
In this paper, an attempt has been made to post process GPS survey data acquired at 15 0, 250,
and 350 satellite elevation angles using TBC, TTC and TGO software packages. The results
obtained from the three packages have been analyzed and compared. Generally these revealed
that the three packages are good for post processing GPS survey data for accurate
determination of position of points on earth surface and the accuracy of position increases with
increase in satellite elevation angle. However, from the comparison of the results, it can be
concluded that TBC software package produces better results, both in baseline and coordinate
domains, than TTC and TGO software packages. This is probably because TBC software package
has proved consistently to be a more excellent processing package in modeling error associated
with GPS survey data. Therefore, amongst the Trimble post processing software packages, TBC
is recommended for GPS survey data meant for large and medium scale geodetic and
engineering surveying projects. The scope of this study is limited to the use of three Trimble
software packages. Therefore, it is recommended that similar study in future should extend the
scope to include other non-Trimble commercial software packages.
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