| Surveying | |
Low Cost GNSS and Geo-referencing of Small Rural Cadastral Surveys
This paper presents challenges faced by surveyors in Jamaica to geo-reference small rural cadastral surveys. An interim solution to the problem is provided. We present here the first part of the paper. The concluding part will be published in the October 2017 issue |
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A recent amendment to the Land Surveyors Regulations (1971) of Jamaica made by the Land Surveyors Board requires that all Cadastral Surveys must be tied to the National Grid. For surveys done in urban areas, a minimum of two (2) boundary points must be used to tie surveys to the National Grid to a positional accuracy of plus or minus 0.1 metre. In the case of surveys done in rural areas, a minimum of two (2) boundary points must be used to tie surveys to the National Grid to a positional accuracy of plus or minus 0.5metre. A temporary exemption, subsequently implemented, allows for surveys done in rural areas, where the Virtual Reference System is not functional and ground control is beyond four hundred metres (400m) of the subject of survey, that such surveys may be geo-referenced to a positional accuracy of plus or minus 3 metres. This presents a problem to define the orientation of the survey, and is one of the aspects of this new requirement which caused some concern to surveyors.
The Surveys and Mapping Division of the National Land Agency has embarked on the production of an island wide digital cadastral map, which will support a myriad of applications, and is one of the reasons why it has become necessary to require surveys to be tied to the national grid, so that this project can be executed more efficiently. Another reason is to support reliable land registration by eliminating dual registration of land.
The implementation of the new amendment will dictate that surveyors acquire Global Navigation Satellite System receivers in order to efficiently meet the new requirements. On the other SURVEYINGhand, the cost of survey grade receivers (Scott, Jones, and James 2016) can be an impediment for some practitioners, who may have to resort to the option of using low cost receivers. However, can these low cost receivers meet the required accuracies as outlined in the Land Surveyors (Amendment) Regulations, 2013? The purpose of this study is to investigate the effectiveness of low cost GNSS in geo-referencing small rural cadastral surveys, by looking at costs and positional accuracy characteristics, using data collected in the field by members of the University of Technology, Jamaica, Surveying & Geographic Information Sciences final year students, the National Land Agency and a private practitioner Mr. Earle Spencer.
Background
Cadastral surveying is that branch of surveying which is concerned with the adjudication, demarcation and survey of land boundaries for the purpose of defining parcels of land for registration in a land registry. The traditional cadastral survey practice typically involve the use of terrestrial survey equipment such as a total station, theodolites and/or a tape/chain, and very often requires the re-establishment of previously existing boundaries points that has gone missing. However of major concern in the current survey practice is the fact that most cadastral surveys are carried out and cadastral plans prepared and lodged at the Surveys and Mapping Division for certification without any requirement for tying the surveys to the National Grid. As a result of this traditional approach, surveys cannot be related reliably to each other, and as a result problems may arise such as dual registration, slow pace of cadastral mapping, and heightened complexity in the re-establishment of land boundaries.
GNSS refers to several constellations of satellites providing signals from space, transmitting positioning and timing data, which when processed, produces positional information for the location of the receiver. The technology is being used in other jurisdictions for the survey of property boundaries and the geo-referencing of land parcels, through adherence to strict legal guidelines and best practices.
Key considerations
The motivation for this study is driven by the following key considerations.
New LS Regulations
According to the Land Surveyors (Amendment) Regulations of 2013, Section 3 subsection C1, surveys are to be tied to the National Grid System. In urban areas, positional accuracy of minimum of 2 boundary points used to connect the urban survey to the Jamaica Datum 2001 shall not exceed, plus or minus 0.1metre, relative to the Jamaica Datum 2001.
Section 3 subsection C2 states that, in rural areas, positional accuracy of minimum of boundary points shall be used to connect the survey to the Jamaica Datum 2001, but shall not exceed, plus or minus, 0.5metre, relative to the Jamaica Datum 2001.
In accordance with the regulation found in under Part IV, section 35D, subsection 3 of the Land Surveyors Act which states “Any Global Positioning System equipment used for the purpose of cadastral mapping, shall be considered inaccurate, if the position it has determined for a point in the National Calibration Network differs by more than plus or minus 0.5 metre from the listed position on the Jamaica Datum 1969 (JAD 69), Jamaica Datum 2001 (JAD 2001) or World Geodetic System 1984 (WGS 84) available in the records of the Surveys and Mapping Division, National Land Agency.”
Where surveys are executed in an area where the VRS not functional and ground control is beyond four hundred metres (400m) of the subject of survey, such surveys may be geo-referenced to a positional accuracy of plus or minus 3metres, by virtue of a temporary exemption. As the ground control is densified and the VRS becomes more accessible, the need for this provision will gradually diminish.
GNSS
Several Global Navigation Satellite System (GNSS) constellations transmit signals which are freely available to users. Some of these constellations are: Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), BeiDou Navigation Satellite System (BeiDou), Galileo, Indian Regional Navigation Satellite System (IRNSS), Quasi-Zenith Satellite System (QZSS), Precise Range and Range Rate Equipment (PRARE), Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS).
The Global Positioning System is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. The first GPS was launched in 1978. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use.
GPS works in any weather conditions, anywhere in the world, 24 hours a day. The GPS position of reference is WGS84. GPS receivers are extremely accurate; however, certain atmospheric factors and other sources of error can affect the accuracy.
Global Navigation Satellite System (GLONASS) was initially developed in the mid 1970’s by the former Union of Soviet Socialist Republics (USSR) based on the experiences with the Doppler satellite system Tsikada. It is made up of 24 satellites, and is operated by the Russian military forces which make it a military system. GLONASS terrestrial reference system is referred to as PE-90.
The People’s Republic of China carried out space activities since the1970s, when it launched its first satellite. China decided to implement an independent navigation system called Beidou. The name Beidou denotes the seven-star constellation also known as Ursa Major, Great Cart, or Big Dipper. This constellation has been used for centuries to identify the Polaris star, which indicates the north direction on the northern hemisphere. The Beidou-2 satellite constellation will consist of 27 MEO satellites with their position of reference been CGCS200.
The Quasi-Zenith Satellite System (QZSS), developed by Japan, provides a regional satellite navigation service in East Asia and Oceania. Although QZSS is primarily an augmentation and a complementary service to GPS, it also has the potential to operate in stand-alone mode providing a regional service. The QZSS coordinate system is known as the Japanese geodetic system (JGS). In May 2006, India approved the implementation of the Indian Regional Navigation Satellite System (IRNSS) to provide an autonomous navigation system for the Indian subcontinent. The space segment consists of seven (7) satellites. IRNSS will provide two types of services, namely, Standard Positioning Service (SPS) which is provided to all the users and Restricted Service (RS), which is an encrypted service provided only to the authorized users. The IRNSS System is expected to provide a position accuracy of around 20 m over the Indian Ocean Region (1500 km around India) and less than 10 m accuracy over India.
The French system Doppler Orbitography by Radio positioning Integrated on Satellite (DORIS) is a one-way uplink system mainly used for the orbit determination of satellites. DORIS became operational in 1990. DORIS instruments are currently in service, and 60 reference stations are operational. The receiver on board the satellite measures the Doppler offsets of these signals every 10 seconds. Based on the measurements, the satellites determine their position with an accuracy of 1m and velocity with an accuracy of 2.5 mms−1 in real time.
The German Precise Range and Rate Equipment (PRARE) is used for orbit determination of satellites like DORIS. It is a two-way system measuring ranges and range rate between the ground segment and the satellites. The master station determines the satellite position in post processing mode with an accuracy of 5 cm and the velocity with an accuracy of 1 mms−1. The system is operational since January 1, 1996.
Low Cost GNSS Receivers
There are many different types or configurations of GNSS equipment ranging from as low as US$150 to US$3,500 or as high as US$ 25,000. Some of the low cost brands of GNSS receivers are manufactured by companies such as Eos Positioning (Arrow), Garmin, Magellan, South, Trimble, Columbus and Wintec and may be used in autonomous mode or differential and single frequency post processed after attaching an external antenna, which adds to the cost of the receiver. Magellan Navigation, Inc. is an American producer of consumer and professional grade global positioning system receivers. Some of the products by Magellan Inc. are the Pro-Mark 3 which is a survey grade system that performs centimetre-accurate static, stop and go, and kinematic surveys, as well as GIS and mapping. There is also the Pro-Mark 500 which does the same thing plus real time kinematic procedures. The Ashtech Pro-Mark is one of the most versatile post-processing solution equipment, designed for easy and efficient land survey applications. It includes a rugged GNSS handheld receiver running a version of the Windows operating system. Magellan also produces a small commercial grade receiver which is targeted at the recreational market.
One of the most common hand held GNSS devices is manufactured by Trimble and called the Geo-Explorer. It is described by the company as a high accuracy handheld device packed full of features that enable fast geospatial data collection anywhere. It may be used in autonomous mode and also in differential mode after attaching an external antenna and post processing the collected data.
Garmin Ltd. is the Swiss parent company of a group of companies founded in 1989. One of the most popular of the Garmin handheld GPS receivers is the compact e-Trex series which was introduced in 2000.
Orientation
The new provisions require that:
Initial orientation of any survey may be obtained by means of observation of control marks:
a. In the National Grid System, Jamaica Datum 2001; or
b. In an adjoining survey, the initial orientation of which was obtained using controls established in the National Grid System, Jamaica Datum 2001.
All other previous provisions, including the use of magnetic north as a means of orienting surveys have been deleted from the regulations. A major consideration now is whether grid north can be achieved to an acceptable degree of accuracy given the temporary relaxation of the standard for rural surveys.
References
[1] Garmin. Garmin. n.d. http://www8.garmin.com/aboutGPS/ (accessed February 19, 2015).
[2] Hofmann-Wellenhof, B, H Lichtenegger, and E. Wasle. GNSS–global navigation satellite systems: GPS, GLONASS, Galileo, and more. Springer Science & Business Media., 2007.
[3] Land Surveyors Board Jamaica. “Land Surveyors Regulations.” Kingston: Government of Jamaica, 1971.
[4] Land Surveyors Board of Jamaica. “Land Surveyors (Amendment) Regulations .” Land Surveyors (Amendment) Regulations. Land Surveyors Board of Jamaica, 2013.
[5] “Land Surveyors Act.” Kingston: Government of Jamaica, 2005.
[6] Magellan. Magellan GPS. n.d. www.highspeedsat.com/magellan-gps.php (accessed February 20, 2015).
[7] Office of the Cheif Surveyor General South Africa. Cheif Surveyor General. n.d. http://csg.dla.gov.za/cadsurv.htm (accessed February 19, 2015).
[8] Schwieger, V. High-Sensitivity GPS – the Low Cost Future of GNSS. Hong Kong, SAR.: FIG, 2007.
[9] Scott, B., Jones, R., and James, K. The implications of the recent amendments to the Land Surveyors Regulations of Jamaica. University of Technology, Jamaica – Final Year Research Project, 2016.
[10] Spectra Precision. Spectra Precision. n.d. www.spectraprecision.com/eng/promark-120.html#.V6K4m7grLIU (accessed February 23, 2015).
[11] Trimble. Trimble. n.d. www.trimble.com/Survey/trimbleGeoXRgnss.aspx (accessed February 24, 2015).
To be concluded in next issue.
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