Laser Scanning for Checking Earth Moving Works

Transcription

1 Tomáš KŘEMEN, Jiří POSPÍŠIL and Bronislav KOSKA, Czech Republic Key words: laser scanning, checking accuracy, earth moving works, DTM SUMMARY Automatically controlled earthmoving machines are currently beginning to find use during carrying out extensive earthmoving works as for example building motorways. The experiment took place on a field situated in the Lahovice. The earthmoving work project used in this experiment contained a DTM of the background layer of the traffic way. It was a 80-metre-long plane section, on which two counter sweeps. A space polar method by means of a total station and a terrestrial scanning system were used to check execution of earthmoving works. The scanning system Leica HDS 3000 was placed approximately in the middle of area of interest so that as big part of the adjusted surface as possible were seen. Evaluation of check measurements were carried out in the Cyclone software. Digital models of height differences between the projected DTM and the DTM from measuring by the total station and from measuring by the scanning system were created. Usability of the laser scanning technology for the check of carrying out ground works with an automatically controlled machine implies from the results of the conducted experiment. 1/10

2 Tomáš KŘEMEN, Jiří POSPÍŠIL and Bronislav KOSKA, Czech Republic 1. INTRODUCTION Automatically controlled earthmoving machines are currently beginning to find use during carrying out extensive earthmoving works as for example building motorways. It is possible to achieve significant time, material and fuel saving and also labour force saving by using automatically controlled earthmoving machines. Automatic control systems can be installed in many types of earthmoving machines as dozers, diggers, graders etc. Automatic control systems consist of three basic components: a control unit, a hydraulic system operating a tool and a navigation system. Two types of navigation systems are used in earthmoving machines a total station (TS) placed outside the machine pointing at receiving and a transmitting sensor placed on the controlled machine and a global navigation satellite system (GNSS) consisting of a reference station placed outside the machine and a station placed on the controlled machine. This is description of the working procedure of an automatically controlled earthmoving machine: Firstly, a digital version of the ground work project is prepared; this version is recorded into a control unit installed together with hydraulics into the machine. A navigation system is prepared afterwards. When using a TS it is necessary to ensure direct visibility between a machine and a total station in the working area. Only one machine can be operated by means of the TS. Direct visibility between reference station and station placed outside the machine does not have to be ensured when using a GNSS. More machines can be operated by means of a reference station. At this moment, the engine driver is already wheeling the machine through the working area and the automatic control system is already setting a tool into a correct position by itself. Check of earthmoving works is carried out by standard geodetic methods as total stations and GNSS. The terrestrial scanning systems have also started to being used for checking at present. The locality is measured before and after grading for check measurement. Measurement before grading also serves as a source of data necessary for project of earthmoving works automatic control. Introduction of automatic machine control results according to manufacturers in significant fuel, material and time saving and increases execution accuracy of earthmoving works. Unfortunately, most manufacturers do not state concrete examples of savings. That is why an experiment with an automatically controlled dozer by means of a GNSS was conducted within a grant number 103/06/0617 called Influence of using progressive technology on acceleration of technological and measuring processes. Check of earthmoving works by geodetic methods and its results will be described in more detailed way in this article. 2/10

3 2. TESTING OF AUTOMATIC CONTROL EARTH MOVING MACHINE 2.1 Location A locality of the building site of the golf course in the cadaster of the Lahovice municipality was chosen for testing the automatically controlled earthmoving works. The experiment took place from 6th to 7th November The preparation works and earthmoving works with the automatically controlled dozer [1] took place on the first day. Check of the earthmoving works by the geodetic methods was carried out on the second day. 2.2 Preparation works The earthmoving works were carried out with the automatically controlled Catepillar D6K XL Dozer with six directions ploughshare, equipped with the Trimble GCS900 earthworking machine control system in the Dual GPS set consisting of two Trimble MS990 GNSS receivers and the CB430 control unit (fig. 1). Fig. 1 The CAT D6K Dozer with the Trimble MS990 GNSS receivers and the Trimble SPS851 rover A communication project was designed for testing. It was a bottom layer of the traffic way in form of letter S. According to the project, the way length was 144 m with constant width 8 m. Superelevation between the start point and the final point was zero. But the line of the way was rugged as for height (fig. 2). 80 m of the line was realized. 3/10

4 Fig. 2 The realized part of the way with data about heights in metres Preparation geodetic works were carried out before beginning the earthmoving works. The Trimble SPS851 reference GNSS station was stabilized near the area of interest. 3 points of the point field were measured in the local system of coordinates. Project calibration (placing into the real terrain) was carried out on one of these points [1]. Focusing the area of interest before beginning the earthmoving works was carried out next. These measurements were carried out with the Trimble SPS851 GNSS rover. 2.3 Track dozer CAT D6K Engine of this dozer Cat C6.6 is a six-cylinder ordinary engine with stroke volume 6,6 l and it is equipped with the Caterpillar Common Rail fuel system. Several innovations are used here, ensuring electronic control of the highest contemporary standard, exact delivery of fuel and inflow of air into the engine. Performance of the engine is high and emissions are extremely low. The engine has a compact construction with components strengthened for heavy duty. Combination of increased growth of turning moment and maximum performance improves response of the engine to the control, ensures higher drawing force and shorter times of shoving cycles. Dozer D6K is equipped with an electronically controlled hydrostatic gear system with separate control and independent operation of performance of each track, which enables fast acceleration, fluent change of speed of the travel and gearing change of direction of the travel forwards / backwards while performance of the engine is full. The electronically controlled 4/10

5 hydrostatic gear system automatically keeps engine revolutions. This corresponds to demands on performance during the given application for achieving the required performance. Hydrostatic gear enables a fluent change of speed of the travel from 0 10 km/h when moving forwards and backwards. This enables an operator to choose optimum speed according to terrain conditions and conducted works. It also does not lead to interruption of performance transmission, which is current during gearing. Transmission of performance on the tracks even when the machine is turning and possibility of countermarch of the tracks increases manoeuvrability of the machine and its productivity. When the D6K turns it comes to deceleration of one track in comparison with the other, but performance is still transmitted on both tracks. The tool the VPAT ploughshare enables hydraulic setting of height of the ploughshare, cutting angle and tilt of the ploughshare from the standpoint of the operator. The dozer was equipped with the AccuGrade GPS system for purposes of the executed measurements. AccuGrade GPS is a levelling system calculating information about position on the machine, comparing position of the ploughshare with the building project, and handing over this information to the operator by means of the display installed in the cabin. Information contain data about height of the ploughshare, necessity to draw aside or heap up material, visual indication of position of the ploughshare over the projected surface and graphical illustration of the projected surface with indication of location of the machine. AccuGrade GPS gives all information that the operator in the cabin needs to carry out the work, the result of which is higher standard of operating. Means for vertical and horizontal guidance lead visually the operator to achieving the required height and slope. Automated functions enable the hydraulic system to control automatically setting of the ploughshare, so that its position corresponded to the required plane. The operator uses guidance means and operates the machine so that the exact heights and slopes were followed continuously, which reflects in higher productivity and in reduction of tiredness of the operator. The measurements that were just carried out proved high productivity of the executed work, when creation of demanding profile with various slopes was carried out in three hours with accuracy resulting from the following chapters. 2.4 Earthmoving works The calibration file from the GNNS rover and the communication project were recorded via compact flash card into the operating unit CB430 placed in cabin of the dozer. The operator saw the current position of the machine and detailed position of the ploughshare towards the project on the colour monitor. Work of the operator consisted only in driving the machine and moving it so that the automatically moving ploughshare copied the roadside or the communication axis. The ploughshare in the automatic regime moved upwards / downwards as necessary. In the situations when it was necessary to draw aside or to heap up larger amount of the material, the operator switched off the automatic operating of the ploughshare and this activity was carried out by the standard procedure. 5/10

6 2.5 Check measurement Check measurement of carrying out the earthmoving works was divided into two parts. On the first day, the graded area was measured by means of the GNSS rover. On the second day, the area was measured by two other geodetic methods, by the space polar method and by the terrestrial scanning. The TOPCON GPT 2006 total station was used for check measurement by the space polar method. The total station was placed approximately in the middle of the area of interest. The total station was attached by the free station method into the local system of coordinates by means of three points stabilized and measured the day before. 100 detailed points in 15 cross sections were measured. The whole measurement was carried out from one standpoint. The point field was extended by the total station by one point to four points for purposes of check measurement by the Leica HDS 3000 terrestrial scanning system. Then the points were signalized by special targets and measured by the scanning system for attachment of the check measurement into the local coordinates system. The scanning system was placed approximately into the middle of the area of interest so as big part of the graded surface as possible was visible. The whole measurement was carried out from one station. 2.6 Processing Before beginning the earthmoving works, the area of interest was measured by means of the GNSS. The detailed points gained from this measurement were used as a base for operating the dozer and for creation of the DTM (digital terrain model) of the area of interest before terrain grading. After finishing the earthmoving works, the communication area was measured with the GNSS rover for carrying out check of the earthmoving works. A DTM of the area was also created from this measurement. DTM from both measurements were created in the Cyclone programme. Processing the measured data from the total station was carried out in the Cyclone programme as well. A DTM after grading of the area of interest was created from the measured detailed points. Measurement from the scanning system was processed as well in the Cyclone programme and its output was a DTM after grading. One DTM before grading and three DTM after grading (the GNSS, the total station and the scanning system) were gained in total from the measurement. A DTM of the project placed in the local system of coordinates was also used for evaluation. 2.7 Results Evaluation of the measured data went on as comparison of volumes and surfaces of cuttings and fillings between the above stated DTM. The gained results are stated in table 1. 6/10

7 Table 1 Comparison of volumes and surfaces of cuttings and fillings - part 1 1. DTM Scanner Scanner Scanner Scanner 2. DTM GNSS after Total station Project GNSS before grading grading Volume of cuttings 21,3 m 3 22,5 m 3 8,5 m 3 94,7 m 3 Volume of fillings 0,4 m 3 0,4 m 3 2,2 m 3 105,8 m 3 Surface of cuttings 504 m m m m 2 Surface of fillings 36 m 2 26 m m m 2 Table 1 Comparison of volumes and surfaces of cuttings and fillings part 2 1. DTM Project Total station GNSS after grading 2. DTM GNSS before grading GNSS before grading GNSS before grading Volume of cuttings 106 m 3 89 m 3 87 m 3 Volume of fillings 119 m m 3 118,6 m 3 Surface of cuttings 284 m m m 2 Surface of fillings 356 m m m 2 Table 1 Comparison of volumes and surfaces of cuttings and fillings part 3 1. DTM Total station GNSS after grading Total station 2. DTM Project Project GNSS after grading Volume of cuttings 1,8 m 3 0,7 m 3 5 m 3 Volume of fillings 16 m 3 16 m 3 4,6 m 3 Surface of cuttings 57 m 2 57 m m 2 Surface of fillings 537 m m m 2 Two DTM are always stated in the table, the first and the second one. When comparing these two DTM, we gained data about amount of cuttings and fillings together with their surfaces related to the first DTM, i.e. how many cuttings and fillings and on how big surface it is necessary to do on the first DTM, so as to gain the second DTM. Difference in sum of surfaces of cuttings and fillings of the individual comparisons is caused by different size of the used DTM. These DTM were not possible to identify for reason of small volume of data gained when measuring with GNSS and with total station. DTM gained from measurement before grading (a wire network) and from measurement with the scanner (a network with grey texture) are displayed in figure 3. It is evident from figure 3 and from the tables that the project was placed into the terrain with the aspiration to achieve a balanced balance of earthmoving works. In the left half it was necessary to heap up soil, whereas in the right half it was necessary to draw it aside. It clearly implies from the stated results that the DTM gained by the method of the terrestrial scanning adheres best to the project. Figure 4 displays comparison of the DTM gained from the scanner (the grey DTM) and of the DTM gained from the project (the black DTM). We also gained from this method the largest amount of information about the stated area thanks to high density of the detailed points (spacing of points approximately in centimetres) in comparison with the other methods (spacing of points in metres). The space polar method and the GNSS method were loaded with systematic error of mild plunge of the rod pike into the terrain during the detailed measurement. That is why their result DTM are lightly plunged under the project DTM. Accuracy of these two methods is further influenced by density of the focused detailed points and by their selection in the terrain. 7/10

8 This result confirms the results from the experiments conducted before dealing with accuracy of the DTM gained by various geodetic methods [2]. When keeping the necessary principles of deployment of the identical points and suitable setting the scanning density, the result accuracy of the DTM gained from the scanning is very high and fully meets the requirements concerning the check method of carrying out the earthmoving works. Fig. 3 Illustration of the DTM gained from the scanner and the DTM before adjustment Fig. 4 Illustration of the DTM gained from the scanner and the project DTM 8/10

9 3. CONCLUSIONS The solving team succeeded in creating a mechatronic system of excellent operating parameters by a suitable combination of the dozer equipped with progressive AccuGrade Laser and the GPS for operating and guidance of the machine with the TRIMBLE building position system (the set consists of the GNSS TRIMBLE SPS851 reference station, the GNSS TRIMBLE SPS 881 mobile station and the TCU operation unit with the SCS900 software). During the experiment the system showed high working accuracy, speed and productivity while achieving labour force saving on geodetic works, operator works and reduction of costs on realization of the project. It implies from the results of the conducted experiment that carrying out the earthmoving works with the automatically operated machine is very accurate with respect to the objective conditions of carrying out the earthmoving works (table 1, part 1, column 3. Approximately 200 m3 of soil on the surface of 560 m2 were removed when realizing the earthmoving works. It implies from the results of the check measurements that the earthmoving works were carried out very accurately with the automatically operated dozer and that the terrestrial scanning is the most accurate method. Automatic operating of the earthmoving machines can be definitely recommended both in terms of the achieved accuracy and in terms of economy of running the machine. REFERENCES [1] Projekt Lahovice, technical report of company Trimble, 2007 [2] KŘEMEN, T. - KAŠPAR, M. - POSPÍŠIL, J.: Operating Quality Control of Ground Machines by Means of the Terrestrial Laser Scanning System. In: Image Engineering and Vision Metrology [CD-ROM]. Dresden: ISPRS, 2006, ISSN [3] JEŘÁBEK, K. VONDRÁČKOVÁ, T.: Koncert pro dozer a GPS. In: Stavební informace 1-2/2008, ročník XV, ISSN ACKNOWLEDGEMENTS This paper has been supported by GAČR no. 103/06/0617 Influence of Use progressive Techniques to a Speedup of Technological and Measuring Processes. BIOGRAPHICAL NOTES Ing. Tomáš Křemen is a doctoral candidate and an assistant lecturer at Czech Technical University in Prague. Testing of terrestrial laser scanning systems and their applications are his specialization. 9/10

10 Ing. Bronislav Koska is a doctoral candidate and an assistant lecturer at Czech Technical University in Prague. Optoelectronic methods of 3D measuring surfaces of objects are his area of interest. Prof. Jiří Pospíšil has 30 years of research practice at CTU in Prague, chairman of branch of the Czech Association of Surveyors and Cartographers, authorised expert in electronics with specialisation in optoelectronic measurement systems, optical quantum generators (lasers) and receptors of their radiation. He is intensively interested in 3D scanning since year CONTACT Ing. Tomáš Křemen CTU in Prague Thákurova 7 Prague CZECH REPUBLIC Tel tomas.kremen@fsv.cvut.cz 10/10