GPS equipment accuracy testing
In general, measurements are only “legal” if they are “traceable” to primary standards of measurement. A GPS measurement is “legally traceable” if: (i) it is carried out using the various test/calibration procedures as required by the Guidelines, and; (ii) the survey has followed the “recommended practices for field and office procedures” as described in the Guidelines.
Zero base line test
The two GPS receivers should be connected to single antenna using an antenna splitter appropriate for the particular brand of receiver and antenna. The slope distance on processing should be less than 3 mm. This test is very simple and should be performed at regular intervals and also before any control survey project is undertaken.
Known base line test
The pair of GPS receivers should be tested by measurement against a known base line of first order accuracy. In India Survey of India has a 13 km base line of first order accuracy near Dehra Dun. Most of the GPS equipment purchased by SOI is tested against this base line. Such test sites can be prepared by number of zero order observations between two inter visible points/stations anywhere by Geodimeters/ Precise EDM instruments. GPS equipment should be checked against such base line periodically. The resulting difference between slope distances should yield accuracy of better than 1 in 50000.
India has a geodetic control network of first order accuracy in which control points are available nearly every 50 km apart. GPS receivers to be tested should be used for observations at such points and processed coordinates can be checked against these. Indian control points known as GTS stations are in Indian system whereas GPS gives coordinates in WGS 84. Therefore a network of at least a braced quadrilateral can be observed, data processed, and adjustment done by least squares. Processing shall yield accuracy also which should be of the first order. This test is most comprehensive and considered the best but it takes considerable time.
It is essential that at least two tests preferably all the three tests should be performed on receipt of the instruments and periodically say every year and before any large control survey project is taken up.
Guidelines for GPS Cadastral urveys in Malaysia
How to perform Zero base line test when technology is evolving so fast that the receiver and the antenna are combined & manufactured as a small unit, in the market like Trimble R8, Unistrong E650?
Good reference from Malaysia GPS Cadastral however is not easy to perform known baseline test in Malaysia as baseline is limited. Most of the baselines were created to cater EDM which needs shaded conditions to perform with less refraction by the heats.
JUPEM is a good organization; however the management seems half sleeping.
No new revised official known geodetic network, since in the nineties, beside GDM2000 network which sometime JUPEM’s lower level staff can not able to cope with technical issue, where JUPEM officers are always busy meeting.
GDM 2000 is good but still not yet fully practical due to now coming to 10 years delayed in delivery the main purpose of practical usage. No software in Malaysia can convert with assurance and confidently from GDM 2000 to local State Cassini and vice versa in every state.
Leave your response!
You must be logged in to post a comment.