SITE MEASUREMENT WITH COMBINATION OF POCKET PC AND GLOBAL POSITIONING SYSTEM FOR PRELIMINARY ARCHITECTURAL DESIGN PROCESS TODSPOL TEDRUMPUN, WALAIPORN NAKAPAN Master of Science Program in Computer-Aided Architectural Design, Rangsit University, Thailand. [email protected], [email protected]

Abstract. This paper presents an alternative method of site measurement for an early design phase. In an early design phase, we consider geomantic information, a kind of technical information crucial for design decision, which can be gathered by a survey. The frame work of this project is originated from a problem of Thai architects’ practice, where we propose GPS system for survey solution. In present day, GPS technology presents various tools to use in survey. However, a high precision GPS device is extremely costly. In this paper we propose low cost devices that give information precise enough to use in an early design phase. To increase accuracy of information, differential equation is used to reduce error of signal altered by atmosphere. Also, information from GPS contains world coordinate information: latitude, longitude, altitude and time, which allows creating 2D map and 3D land form. Architect can instantly use results of site information for many purposes, such as on-site meeting, early design planning and layout design.

1. Introduction In present day, many Thai architects prepare their project design material by basing on the land shape on the back of a title deed to a piece of land. They have to turn this land map to digital data to work with while waiting for site measurement report from survey engineers. Site survey report is quite expensive and use a lot of man hours, where architects spend a along time waiting for. During this time, architects must attend a site meeting or a site visit and get some perspective of the site. They use some basic measurement techniques such as tape measure, foot step measure, etc. to check out the (in)

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TODSPOL TEDRUMPUN, WALAIPORN NAKAPAN

accuracy of site dimension from the title deed. After that architects start preliminary design, create concept, layout and master plan, but the accuracy of this early design is very poor. First of all, information on the title deed is often inaccurate since the government allows up to 20% error. Besides, the original documents scale is too small; from 1:2,000 to 1:5,000. When enlarged to a useable scale such as 1:500 or 1:200, the result unavoidably contains some errors in shape and size. Moreover, the information on this 2D map does not contain at all some other useful information such as existing building, tree, stream, pond, road etc. If the project locates on a sloped area, 3D information such as the land contour is also crucial for the accuracy of the design. This routine procedure of Thai architects to prepare their early design land map cannot provide a satisfactory solution at all. 2. Use Alternative Technology solve problem While looking for a new method to solve the information inadequacy, we are interested in Global Positioning System (GPS) technology. This technology allows us to identify position of everything out of its signal shade, wherever the sky can be seen. Nowadays, many transportation businesses use GPS to guide and control vehicles such as trucks, ships, airplanes and even automobiles to a destination because of its useful potential (The Complete Vehicle Management System. March 7, 2000). Further more NAVSTAR (NAVigation Satellite Timing And Ranging – the name given to GPS satellites) has recently turned off the Selective Availability (S/A use for jamming signal precision in condition to military activity and terrorist). This means any public with a GPS receptor have a free access to this accurate information. Global Positioning System technologies provide useful potential of world coordinate information: Latitude, Longitude, Altitude, and GPS Time. The Cartesian coordinate inaccuracy is now reduced to 15 meters RMS (RootMean Square) from 100 m. horizontal and 156 m. vertical in the past. If we have a good instrument or use a Differential GPS equation, we can reduce the inaccuracy to 2.5 m. RMS (Wichiencharoen, C. & Satirapod, C., 1997). The accuracy rate will increase to a larger piece of land; if we expect site accuracy to no more than 5% error from survey report, the site must be at least 50*50 m2. However, if project site was independent, project doesn’t need to refer its position to others, the information is precise-itself.

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SITE MEASUREMENT WITH COMBINATION OF POCKET PC AND…

3. Low cost device, easy to use and carry around High precision GPS device is extremely costly. That’s why we turn to a low cost device. Handheld device units can be used to collect coordinate information, process, and display into 2D & 3D graphics such as boundary, perimeter, existing coordinate, 3D landform etc. In our approach, we consider the potential of a PDA (Personal Digital Assistants) with a high speed processor, a color display and a GPS receiver unit. By adding a computer program to process all required information, a simple PDA, affordable by most architects, can be changed to a site measurement device. 4. The System DGPS system requires two parts of GPS receiver unit: a static receiver (reference received) and a dynamic receiver (field receiver). Static receiver is used for tracing various data every epoch. Data will be then sent to field receivers.

figure1. Show DGPS Basic system

The following elements of system are proposed (figure1): 4.1. Control station GPS receiver or reference receiver is static part to receive GPS signal. As signal are not unstable because of physical effect (called GPS Errors), Ionosphere, Troposphere, Multipath Error (http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html). Control station will record variation of data each epoch and send to other part of the system to correct raw coordinate. These control stations are available all

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TODSPOL TEDRUMPUN, WALAIPORN NAKAPAN

over Thailand for use in government activities by sending correct GPS data via radio transceiver. In nearly future, Thai Government will open radio frequency source to public then everyone within the frequency range can use the system without Control station. In this experiment, we must create our own control station by using a laptop computer and send correction data to kinematics GPS receivers via wireless network. In case of signal shade or out of range, we can correct received data using an asynchronous system. 4.2. Kinematics GPS receiver or field receiver is a mobile device moving across the site to collect data. We can use more than one field receiver to save time of collecting site information. Data can be distinguished into two groups by their characteristics: - Single point: tree position, pole, altitude of ground record and display as point value, - Group of points: building, road, pond, perimeter etc record and display data as an object. Raw data will be recorded and are editable for update. Group of raw data can hided or displayed for easy to work in small screen. Raw data must be recalculate by using correction data from control station via wireless network (Synchronous) call Real Time Kinematics or get correction data later (Asynchronous). Information can be used in meeting presentation immediately on PDA units or sent to regular computer in standard data format of CAD application (.dwg, .dxf, .txt). This information is then read to be used in the next phase of the design. 5. Programming Design 5.1. CONCEPT

As DGPS system requires two part of function as server and client. We consider designing an application that contains both functions for easy to use in every type of computer. Both path of system receive same massage from GPS Satellites (The National Marine Electronics Association-NMEA massage) and translate to coordinates value (X, Y, Z) at the same epoch. Program will record data and send to the other path. (Figure2.)

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Figure 2. System Devices Diagram

In real-time mode, field receiver will collect point data and recheck variation of data at reference receiver in order to compute accuracy value and then display precise 2D map or 3D land form. In asynchronous mode, field receiver collects point data and record. Data can be displayed in 2D map or 3D land form but the results may not precise since raw data are not yet corrected. After that field receiver can get corrected data from reference receiver and recomputed all data. This final data is more precise. (Figure 3.) Reference receiver contains following functions: - Collect points and calculate variation of data, - Convert data units , - Process data, display and save, - Send corrected data to field receiver via wireless device, - Synchronous data from field receiver. Field receiver contains following functions: - Collect points or group of data, - Convert data units , - Process data, display, edit, update and save, - Receive corrected data and recomputed (DGPS), - View results in 2D or 3D modes,

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TODSPOL TEDRUMPUN, WALAIPORN NAKAPAN

Real Time Mode

Asynchronous Mode

Figure 3. System Data Flow Diagram

5.2 APPLICATION FUNCTIONS

Application functions are shown in Figure 4. There are three parts for this application. 1.

File: group of functions containing command of device and file system such as devices setting, satellites status, unit setting, create new project, open old project, compute data, import and export data, recomputed DGPS equation, etc.

2. Edit: group of functions containing command of editing collected data such as: add data, edit data and erase data. Collected data may be group of data (land form, existing building, pond, boundary etc.) or individual data (tree position, pole etc.) 3. View: group of functions containing command of display results, in 2D modes (Figure 5).

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Figure 4. Application Functions Diagram

Figure 5. GPS Status and collect data modes

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TODSPOL TEDRUMPUN, WALAIPORN NAKAPAN

Figure 6. 2D map mode and 3D Land form mode

The expected results of this experiment are: 1. Propose an alternative method to get useful site information, 2. Reduce waiting time for engineer reports form a few months to a day with no extra cost, 3. Display information in 2D & 3D graphics, which helps architect making a good design decision, 4. Propose a mobile system easy to carry around in wild area and friendly to use with high performances. 6. Conclusion. GPS technology is a good option for architects. It proposes useful geomantic information for an early design phase. It brings us close to reality design without waiting for traditional site survey. However, GPS technology continues to develop. In the future, it is predictable that the technology will give us more precise devices with lower cost. Finally this system can be stand alone by receive corrected data form government provide that we can add only radio receiver to system devices. The following problems are found in this experiment: - PDA battery runs out in 2.5 hours. Collecting data must be finished in time or use battery more than one unit.

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Building perimeter data may not precise in condition of multipath error. Then we ask “How can data be collected without multipath errors?”

This device is under development. The next step of this experiment is the precise rates of this system and develops it more precise for acceptable use. New GPS technologies such as wireless and blue tooth devices lead us to new procedure of surveying system. References Global Positioning System Standard Positioning Service Specification: 2nd Edition, June2, 1995. Available on line from United States Coast Guard Navigation Center Hoffmann-Wellenhof, B. H. Lichtenegger, and J. Collins. 1994. GPS: Theory and Practice. 3rd ed.New York: Springer-Verlag. Institute of Navigation. 1980, 1884, 1986, 1993: Global Positioning System monographs. Washington, DC: The Institute of Navigation. J. David Boal, December 1992: Guildlines and specifications for GPS surveys Release 2.1., Director & Dominion Geodesist Geodetic Survey Division Surveys, Mapping & Remote Sensing Sector EMR Canada Leick, Alfred. 1995: GPS Satellite Surveying. 2nd. ed. New York: John Wiley & Sons. Leick, Alfred: GPS Satellite Surveying. 2nd ed. A wiley-international Publication, 1997 National Imagery and Mapping Agency. 1997. Department of Defense World Geodetic System 1984: Its Definition and Relationship with Local Geodetic Systems. NIMA TR8350.2 Third Edition. 4 July 1997. Bethesda, MD: National Imagery and Mapping Agency. Available on line from National Imagery and Mapping Agency NAVSTAR GPS User Equipment Introduction. 1996. Available on line from United States Coast Guard Navigation Center Parkinson, Bradford W. and James J. Spilker. eds. 1996: Global Positioning System: Theory and Practice. Volumes I and II. Washington, DC: American Institute of Aeronautics and Astronautics, Inc. Paul R. Wolf, Charles D.Ghilani: Elementary to GeomaticSurveying: An introduction. 10TH ed. Prentice Hall, 2002 Rizos, C. and Satirapod, C. (2001): Differential GPS: How good is it now?, Measure & Map, 15, 28-30. Rizos, C. and Satirapod, C. (2001): GPS with SA off: How good is it?, Measure & Map, 12, 19-21. Rizos, C., Satirapod, C., Chen, H. and Han, S. (1999): GPS with multiple reference stations: surveying scenarios in metropolitan areas, 6th South East Asian Surveyors Congress, Fremantle, Australia, 1-6 November, 37-49. Satirapod C., Wang J. and Rizos C. (2001): Modelling residual systematic errors in GPS positioning: Methodologies and comparative studies, IAG Scientific Meeting, Budapest, Hungary, 3-8 September. Satirapod, C. (2001): Improving the accuracy of static GPS positioning with a new stochastic modelling procedure, 14th International Technical Meeting of the Satellite Division of the U.S. Inst. of Navigation, Salt Lake City, Utah, 11-14 September.

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TODSPOL TEDRUMPUN, WALAIPORN NAKAPAN Satirapod, C., Ogaja, C., Wang, J. and Rizos, C. (2001): An approach to GPS analysis incorporating wavelet decomposition, Artificial Satellites, 36(2), 27-35. 4 / 6 Satirapod, C., Rizos, C. and Han, S. (1999): GPS single point positioning: An attractive alternative?, 4th International Symposium on Satellite Navigation Technology & Applications, Brisbane, Australia, 20-23 July, paper 47. Satirapod, C., Rizos, C. and Wang, J. (2001): GPS single point positioning with SA off: How accurate can we get?, Survey Review, 36(282), 255-262. Satirapod, C., Wang, J. and Rizos, C. (2001): A new stochastic modelling procedure for precise static GPS positioning, Zeitschrift fur Vermessungswessen, 126(6), 365-373. T.A. Musa, J. Wang, C. Rizos, C. Satirapod: Stochastic Modelling for Network-Based GPS Positioning. Presented at SatNav 2003 The 6th International Symposium on Satellite Navigation Technology Including Mobile Positioning & Location Serivces.,Melbourne, Australia 22–25 July 2003 T.J.M. Kennie, G. Petrie: Engineering Surveying Technology. John Wiley & Sons, 1989 The Complete Vehicle Management System: March 7, 2000. [On Line] http://www.cselectronics.co.uk/ Wang, J., Satirapod, C., and Rizos, C. (2002): Stochastic assessment of GPS carrier phase measurements for precise static relative positioning, Journal of Geodesy, 76(2), 95-104. Wichiencharoen C. and Satirapod, C. (1997): Accuracies obtainable from commercial GPS hardware and software, Thailand Journal Engineering (in thai), October.

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