Abstract:
The primary geodetic control network of Sri Lanka, the backbone of geospatial
activities, was established and maintained by the Survey Department of Sri
Lanka. This was established in 1930 using triangulation and was later upgraded
using Global Positioning System (GPS) technology in 1999. Over the past two
decades, most geospatial activities in Sri Lanka have been conducted with
reference to this Sri Lankan Datum 1999 (SLD99). With the ongoing drastic
improvements of Global Navigation Satellite System (GNSS) infrastructure in
Sri Lanka, an epoch-by-epoch realisation of the International Terrestrial
Reference Frame (ITRF) is essential so that spatial data of global, local, national
and regional origins can be easily integrated. This study examined the positional
deviation of Sri Lankan primary geodetic control network stations concerning the
ITRF realisation. A 72-hour GNSS observation campaign was performed over
eight ‘AA-grade’ primary stations, and positional solutions were comparatively
analysed through the Precise Point Positioning (PPP) technique. The results
indicate a significant divergence of around 0.60 m and 1.10 m in the East and
North coordinates, respectively, compared to the existing SLD99 datum. The
deviation in the East direction is higher (around 1.18 m) at Colombo, situated in
the western part of the country, while the deviation linearly decreases towards the
eastern part of the country, reaching its minimal deviation of around 1.07 m at
Ampara. The positional displacement in the Southern region is high (around 0.64
m) at Matara compared to moving along the northward direction, reaching the
lowest value of around 0.42 m at Jaffna. Rather than the timely realisation of
ITRF, the bias in computation and processing during the establishing of the
geodetic control network and utilization of unimproved GNSS technology could
be some reasons for this immense deviation in the Sri Lankan primary control
network. Therefore, this study highlights the timely requirement to upgrade the
Sri Lankan geodetic datum based on ITRF realization with the modern
advancement of GNSS.
