Surveying & Built Environment Vol. 22 Issue 1 (December 2012)

SBE
86
Direct Geo-referencing and Orthophoto Correlation with Demarcation District Sheets
CoNCluSIoN
In this paper, two methods (direct
georeferencing and orthophoto
The “direct” method relies on several
long-lasting (1905 ~ nowadays) stable
features as the control points. Those
features’ coordinates can be surveyed
at a centimeter level and can be directly
applied for georeferencing. This useful
method is however limited by the
availability of surviving control points.
The “indirect” method relies on several
long-lasting (1905 ~ 1963) stable
features. From the 1960s aerial photos,
the agricultural occupation patterns
were maintained largely as in the 1905
NT. Based on those widely distributed
common features, the DD Sheet can be
correlated onto the orthophoto, besides,
an assessment of the correlation
accuracy can be provided.
We surveyors understand that the
DD Sheet was a good survey record
depicting agricultural occupations in
the 1900s. As it is limited by the scale
used at the time of survey, surveyors
need to use other technological means
to accurately delineate lot boundaries.
Orthophoto images are certainly a very
correlation) are applied to derive
horizontal coordinates from DD Sheets.
Table 1 lists the merits and demerits of
these two methods in this paper.
Table 1: Comparisons between two applied methods
helpful means. The orthophoto model
used in this paper used 11 accurate and
permanent features. Other village areas
may not have similar conditions. The
Survey and Mapping Office works on
the full coverage of orthophoto images
to Hong Kong. Should this product be
available to industry, surveyors can
easily delineate boundaries with reasons
and accuracy attached.
ACKNoWlEdGMENTS
This paper is supported by PolyU
G-YH52 & BQ-13C funding.
REfERENCES
Dawe H G (1969), Aerial Survey:
Colony of Hong Kong, The
Photogrammetric Record, 6:34, 335-
347.
Empson H E (1969), Correlation
of D.D. Sheets and Survey Sheets,
Drawing Office Instruction No.11, New