Experience of Using Total Station and GNSS Technologies for Tall Building Construction Monitoring
Abstract
In prevalent engineering practice, geodetic measurement techniques are commonly applied for structural monitoring. For a long time, triangulation, trilateration and levelling techniques have been trusted for the determination of structural deformation and point displacement, with excellent outcomes. With the advent of robotic total stations, the threedimensional topographic measurement method has been proposed as an efficient and rapid measurement option for the determination of 3D coordinates. In addition, the GNSS (Global Navigation Satellite System) technology improvements, mainly in the RTK (RealTime Kinematic) measurement mode, opened a new perspective for monitoring, which has also shown consistent results. However, there are some situations where the use of total station or GNSS technology individually is not enough to perform the monitoring. The solution may then be the combination of both technologies. In this paper, we present the details of two proposed measurement methods and the results of a testing campaign carried out to monitor the construction of “La Costanera Tower”, in Santiago, Chile, using a total station combined with GNSS receivers. These methods are based on the use of GNSS antennas and total station installed on the underconstruction building floor. Having this scenario, two measurement procedures were applied. The first one was based on using a total station coupled with a GNSS receiver, for determining the position of the monitoring point and a GNSS antenna coupled with prism reflector, for the orientation of the total station. The second procedure was based on using a total station and two GNSS antennas coupled with prism reflectors. With this equipment, directions and distances were measured, to determine the position and orientation of the total station, by means of a Free Station positioning computation. The testing results have been compared with traditional measurement techniques. The results showed that the proposed methods could be a suitable solution for monitoring tall building construction.
Keywords
Geodetic monitoring Tall building monitoring GNSS Total station Free Station Polar measurement1 Introduction
Structural monitoring by using geodetic methods is an engineering practice, that is already very well established in the technical and scientific community. For a long time, it has relied on triangulation, trilateration and levelling techniques for the determination of structural deformation and point displacement with excellent results, as seen in US Army Corps of Engineers (2002) and Bird (2009). Recently, with the arrival of robotic total stations, the threedimensional topographic measurement method has been proposed as a faster measurement option for this type of work, as described in Beshr and Kaloop (2013). Installation facilities based on this method are found in many applications of geodetic monitoring, especially those related to mining and construction of large structures, as shown in Afeni and Cawood (2013). Several application programs based on these geodetic measuring methods are commercially available and have been used successfully, such as GeoMoS from Leica Geosystems, among others. With the improvement of GNSS technology, in both postprocessing and RTK modes, it opened up a new perspective for structural monitoring, which has also shown consistent results in the analysis of deformations and displacements, as shown in Yi et al. (2012). However, there are some situations where the use of total stations or GNSS technology alone is not enough to perform the proposed monitoring. A typical example of such a situation is the monitoring with total station in areas where the control points cannot be installed outside the area of influence of the structural displacement, such as, in some cases of slope monitoring of open pit mines. In the case of monitoring with GNSS technology, the difficulty of installing the GNSS antenna at all points of the monitored structure is a typical issue, thus requiring the complementation with total stations and prism reflectors. In such cases the solution is the combination of both technologies – GNSS and total station measurements, as shown in Van Cranembroeck (2011).
This article presents the results of the structural monitoring test carried out during the construction of “La Costanera Tower”, in the city of Santiago, Chile  the tallest building ever built in Latin America. Due to this fact, to ensure the verticality of the building and to monitor its movements, the builders conducted tests with different monitoring methods, among which stood out the use of electronic inclinometers and geodetic monitoring techniques. Regarding the latter, three methods of measurements with installations of instruments on the underconstruction floor were tested because some monitoring points of the building could not be sighted from ground stations. The methods include: (i) Free Station positioning method, based on the use of a total station, installed on the underconstruction floor, and strategically installed landmarks in the terrain, surrounding the construction area of the building. (ii) Polar measuring method, based on the use of a total station coupled with GNSS receiver, to determine the instrument position, and one GNSS antenna coupled with a prism reflector, for the orientation of the total station, both installed on the underconstruction floor. (iii) Free Station positioning method, based on the use of a total station and two GNSS antennas, coupled with prism reflectors installed on the underconstruction floor.
2 La Costanera Tower
The two main reasons for the construction monitoring of “La Costanera Tower” were: to investigate the structural behaviour, when stressed out by wind action and to control the construction verticality. As the building grew vertical, it provided more area for wind exposure. From the structural point of view, the wind “pushes” the building and this action deforms it in the direction of the wind. However, it occurs for tall buildings, the wind rounds the building, generating a rhythmic force perpendicular to the wind, causing the building to oscillate dynamically, generating discomfort to users. To better understand this effect, a model of the building was fabricated, in a scale of 1:400, which was required for simulation purpose in wind tunnel. The simulation results, guided the structural design and the construction of the building.
Although the structural behaviour of the building has been evaluated in detail by means of simulation in the wind tunnel, it was considered prudent to monitor its movements and deformations to ensure the validity of the structural model and the verticality of the building. For this purpose, the builders proposed, use of various monitoring methods, including the concept of geodetic monitoring, by integrating polar measurement techniques with total stations and GNSS technology, as described in this text.
3 Instruments
Surveying instrument for Polar measurements.
Instrument  1 robotic total station: model TCRA1201R300 
Angular accuracy  1.0” 
Linear accuracy  1 mm + 1 ppm 
Range  2.8 km (normal conditions) 
Tracking method  ATR and signal returning 
GNSS instruments.
Instrument  1 GNSS receiver, model GRX1200, 2 GNSS receivers, model GX1230Plus and 1 GNSS receiver, model ATX1230 
Channels  120 channels L1 e L2, GLONASS 
Linear accuracy  3 mm + 0.5 ppm 
Position accuracy  10 mm + 0.5 ppm 
Measurement range  30 km RTK, >30 km postprocessing 
Position rate  20 Hz 
4 Monitoring Methodology and Testing Objective
 (a)
Measurement with total station, installed on the underconstruction floor and prism reflectors, installed on reference points deployed on the ground. This is a conventional measurement method, which was considered as a reference to the other ones.
 (b)
Measurement with total station coupled with a GNSS receiver and prism reflectors, installed on the underconstruction floor.
 (c)
Measurement with total station and prism reflectors coupled with GNSS antennas, installed on the underconstruction floor.
 1.
To check the consistency between the results obtained with polar measurements, through total station and prism reflectors, and the results obtained by combining GNSS and total station measurements.
 2.
To check if the methodology of coupling total station with GNSS receivers maintains the levels of accuracies achieved with measurements through GNSS technology, in RTK mode.
 3.
To establish an operational routine based on the obtained results.
The first step of taking measurements was to install the total station over a forced centring pillar, targeting three control points on the ground, calculating its coordinates by Free Station positioning method, aiming the two monitoring points (P1) and (P2) and calculating their coordinates by Polar measurement method. The coordinate values obtained by this process were adopted as reference coordinates (true values). The second step of the measurements was to determine the coordinates of the total station by means of the GNSS receiver, coupled with the total station and orienting the measurement system backing to one of the prism reflectors coupled with GNSS antenna  (E2) or (E3), whose coordinates were computed by GNSS postprocessing mode. The coordinates of points (P1) and (P2) were determined afterwards by Polar measurement method. The third step of the measurements was to determine the coordinates of the total station through the Free Station positioning method, aiming the points (E2) and (E3), whose coordinates were determined by the GNSS antennas, in RTK mode. Then, aiming the monitoring points (P1) and (P2), for calculation of coordinates by the Polar measurement method.
The consistency of measurement methods has been proven by comparing the results obtained from of the second and third method of measurements with the results of the first one.
4.1 Polar Method

\( X_{S} ,Y_{S} ,H_{S} \) = coordinates of station point (S)

\( X_{P} ,Y_{P} ,H_{P} \) = coordinates of survey point (P)

\( d^{\prime}_{SP} \) = slope distance from point (S) to point (P)

\( z_{SP} \) = vertical angle at station (S)

\( \varphi_{SP} \) = horizontal direction from point (S) to point (P)

\( h_{i} \) = instrument height at station (S)

\( h_{r} \) = reflector height at point (P)
These equations are included in almost all total stations, allowing measurements and computation to be done almost automatically.
4.2 Free Station Method
 \( v\varphi_{SP} \)

= azimuth residual
 \( vd_{SP} \)

= distance residual
 \( vz_{SP} \)

= vertical angle residual
 \( d\omega_{P} \)

= correction to the initial approximation of unknown instrument orientation
 \( a = {{\cos {{\textit{(}{\varphi_{SP}}\textit{)}}_0}} \over {{{\textit{(}{d_{SP}}\textit{)}}_0}}} \)

\(\phantom{0} \)
 \( b =  {{sen{{\textit{(}{\varphi_{SP}}\textit{)}}_0}} \over {{{\textit{(}{d_{SP}}\textit{)}}_0}}} \)

\(\phantom{0} \)
 \( {\textit{(}{\varphi_{SP}}\textit{)}_0} \)

= approximation of unknown azimuth
 \( {\textit{(}{d_{SP}}\textit{)}_0} \)

= approximation of horizontal distance
 \( dx_{S} \)

= correction to the initial approximation of coordinate \( {\textit{(}{X_S}\textit{)}_0} \) of point station (S)
 \( dy_{S} \)

= correction to the initial approximation of coordinate \( {\textit{(}{Y_S}\textit{)}_0} \) of point station (S)
 \( r_{SP} \)

= measured direction from point station (S) to reference point (P)
 \( {\textit{(}{\omega_S}\textit{)}_0} \)

= approximation of unknown instrument orientation
 \( d_{SP} \)

= measured horizontal distance from point station (S) to reference point (P)
 \( dH_{S} \)

= correction to the initial approximation height of point station (S)
 \( z_{SP} \)

= measured vertical angle at point station (S) to reference point (P)
 \( {\textit{(}{z_{SP}}\textit{)}_0} \)

= approximation of vertical angle at point station (S) to reference point (P)
 \( {\textit{(}{d^{\prime}_{SP}}\textit{)}_0} \)

= approximation of slope distance from point station (S) to reference point (P)
5 Measurement Procedures and Results
5.1 GNSS Observation
5.2 Coordinate Transformation for Adequate GNSS Measurement from the Local Coordinates
Topographic control points and WGS84 coordinate values.
Point name  X (m)  Y (m)  H (m)  Latitude  Longitude  Ellipsoidal height (h) (m) 

M1  458.345  937.665  103.236  33° 24′ 58.84864″ S  70° 36′ 26.03582″ W  644.912 
M2  388.456  819.291  100.747  33° 25′ 02.40038″ S  70° 36′ 29.25537″ W  642.402 
M3  495.816  996.677  104.191  33° 24′ 57.08806″ S  70° 36′ 24.33003″ W  645.859 
M4  675.313  890.564  107.192  33° 25′ 01.18633″ S  70° 36′ 17.90749″ W  648.901 
M5  672.598  818.321  105.915  33° 25′ 03.50512″ S  70° 36′ 18.33858″ W  647.589 
M6  612.649  612.978  102.809  33° 25′ 10.55112″ S  70° 36′ 21.76643″ W  643.005 
M7  348.935  706.947  99.097  33° 25′ 05.87274″ S  70° 36′ 31.28013″ W  640.726 
Coordinate transformation results.
2DHelmert transformation  

Homologous points  6  
Rotation origin  X0  0.001 m  
Y0  0.000 m  
Order  Parameter  Value  rms 
1  dX  861.578 m  0.005 m 
2  dY  506.577 m  0.005 m 
3  Rotation  −6° 40′ 54.85538″  0° 00′ 06.13429″ 
4  Scale  108.2437 ppm  29.7367 ppm 
Height transformation  
Homologous points  6  
Transformation accuracy (mean)  0.014 m  
Parameter  −0.00007955  −0.00014653  541.669 m 
Height inclination on X  −0° 00′ 16.40837″  
Height inclination on Y  −0° 00′ 30.22398″ 
Coordinate transformation residuals.
Point  Point type  dX (mm)  dY (mm)  dH (mm) 

M1  Position & Height  2  5  7 
M2  Position & Height  0  5  6 
M3  Position & Height  −12  0  −12 
M4  Position & Height  18  3  15 
M5  Position & Height  −18  −11  −13 
M6  None       
M7  Position & Height  9  −3  −3 
Note that the point (M6) was not used in calculating the coordinate transformation as its postprocessing residuals, indicated high values compared to other control points. The transformation parameters determined were then inserted in the memory of the GNSS receivers to comply with the topographic building coordinates during monitoring procedures.
5.3 GNSS Measurement and Polar Measurements
GNSS observations were performed in the base station receiver (E1), by recording postprocessing data and transmitting RTK corrections, and in the GNSS receivers (E2), (E3) and (E4), by recording postprocessing data and receiving RTK corrections for real time coordinate computation of each station.
6 Results
GNSS base station coordinates.
E (m)  N (m)  H (m) 

458.345  937.665  103.236 
Coordinate values of total station (E4).
Measurement method  X (m)  Y (m)  H (m)  ΔX (mm)  ΔY (mm)  ΔH (mm)  Spatial vector (mm) 

Method 1: E4 coordinate values computed by Free Station positioning method using ground control points – considered as true values  510.635 ± 2.1 mm  890.502 ± 2.3 mm  161.893 ± 2.7 mm  Reference point  
Method 2: E4 coordinate values computed by total station coupled with GNSS receiver in postprocessing mode  510.640 ± 0.8 mm  890.494 ± 0.9 mm  161.869 ± 1.3 mm  −5  8  24  26 
Method 3: E4 coordinate values computed by Free Station method using E2 and E3 as control points determined by GNSS RTK mode  510.644 ± 3.1 mm  890.485 ± 3.5 mm  161.864 ± 9.4 mm  −9  17  29  35 
Coordinate values of monitoring point (P1).
Measurement method  X (m)  Y (m)  H (m)  ΔX (mm)  ΔY (mm)  ΔH (mm)  Spatial vector (mm) 

P1 coordinate values computed from E4 on Method 1  520.808 ± 2.2 mm  887.186 ± 2.4 mm  161.877 ± 2.9 mm  Reference point  
P1 coordinate values computed from E4 on Method 2  520.811 ± 1.1 mm  887.182 ± 1.1 mm  161.872 ± 1.6 mm  −3  4  5  7 
P1 coordinate values computed from E4 on Method 3  520.828 ± 3.2 mm  887.171 ± 3.6 mm  161.861 ± 9.4 mm  −20  15  16  30 
Coordinate values of monitoring point (P2).
Measurement method  X (m)  Y (m)  H (m)  ΔX (mm)  ΔY (mm)  ΔH (mm)  Spatial vector (mm) 

P1 coordinate values computed from E4 on Method 1  500.802 ± 2.2 mm  896.328 ± 2.4 mm  161.903 ± 3.0 mm  Reference point  
P1 coordinate values computed from E4 on Method 2  500.815 ± 1.1 mm  896.331 ± 1.1 mm  161.892 ± 1.6 mm  −13  −3  11  17 
P1 coordinate values computed from E4 on Method 3  500.829 ± 3.3 mm  896.322 ± 3.6 mm  161.894 ± 9.4 mm  −27  6  9  29 
7 GNSS Coordinate Values Variation of Points (P1) and (P2) Over Around 30 min Time
It is observed that the variations of coordinates obtained in this period are the result of variations inherent by the GNSS technology and due to the movement of the building. The tower was at a height of approximately 60 m at the time of the test. Graphic 1 represents the variation of the coordinates of monitoring point (P1) on GNSS Postprocessing mode, and Graphic 2 represents the variation of the coordinates of monitoring point (P1), on GNSS RTK mode. Indeed, these movements affect the coordinate values of the total station and of the reference prisms installed on the floor of the building. However, as both instruments are anchored in the same structure, they suffer the same displacements, which ensures the effectiveness of measurement methods applied.
8 Conclusions
The test showed that the geodetic monitoring methods by means of coupled GNSS receivers with total station, installed on the floor of the building, produce consistent results when compared with the conventional method of measurements, having only one total station installed on the floor of the building and control points on the ground. The variations found in comparisons of the results are due to the deterioration of the accuracy of GNSS measurements itself.
As expected, and according to Table 7, the differences between the coordinates of measuring point (E4), determined by GNSS measurements in post processing mode and the coordinates of the same point determined by Free Station positioning method, are smaller than the coordinates of point (E4), determined through Free Station positioning method based on control points with coordinates determined through GNSS measurements in RTK mode. The same tendency of accuracy variation is verified in Tables 8 and 9 for the monitoring points (P1) and (P2). Although the sample is restricted, the results indicate that, for the particular situation of this test, the positioning method based on GNSS measurements in postprocessing produces acceptable values for this kind of geodetic monitoring. Furthermore, the results obtained with GNSS measurements in RTK mode, indicate that the proposed measurement method requires further research to assess its suitability for this kind of geodetic monitoring.
It is important to emphasize that the work presented in this paper is the result of a single test, with little measurement redundancy. The authors consider that its scientific value lies in the fact that it was carried out in practical work conditions, still allowing interesting measurements to be properly taken.
Notes
Acknowledgments
This work was carried out by the help of many supporters, which we appreciate enormously.
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