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

The internal orientation parameters are
unavailable. With the knowledge of the
camera RC8 Aviogon 152.4mm lens
(Dawe, 1969), we used approximate
values for the internal orientation
and it worked well (internal accuracy
at about 7 microns). We performed
exterior orientation using currently
identifiable features with surveyaccurate
coordinates. These features
include wells, wall corners, bridges,
graves and sharp path junctions. The
subject agricultural area terrain in this
paper is flat. An auto-generated DEM
for orthorectification is considered
sufficient. The orthophoto image used
in this paper had a tested horizontal
accuracy of 0.3 metre (Tang & Guan,
2010).
Correlation of DD Sheet onto the
Orthophoto of 1963
Correlation in a GIS environment is
done using the geo-referencing function.
Based on the DD Sheet images, the field
bunds were traced to form polylines.
Similarity transformation and affine
transformation were used. In correlation
examples here the affine transformation
was adopted because the Northing and
Easting grid lengths of the adopted DD
Sheet (DD 106) image were found to
vary slightly.
Four blocks of lots were identified with
Surveying and Built Environment Vol 22, 74-87 Nov 2012 ISSN 1816-9554
areas 100m x 100m, 200m x 200m,
300m x 300m and 400m x 400m.
Each block was tested with different
combinations of control points. In
figure 5, showing the test on 100m x
100m, 22 nodes were selected and 3 of
them (No.3, 15 and 19) were assigned
with higher weights. The mean of the
misclosures is 2.0 metres and standard
deviation at 1.6 metres. figure 6 gave
the result using other 3 control points.
The mean is still 2.0 metres.
In figure 7 and 8, for the testing area
of 200m x 200m, the two means are 2.3
metres and 1.9 metres. In figure 9 and
10, for the testing area of 300m x 300m,
the two means are 1.8 metres and 2.1
metres. In figure 11 and 12, for the
testing area of 400m x 400m, the two
means are 2.0 metres and 2.1 metres.
From these tested samples, we could say
only that the subject 1:3960 DD Sheet
can be correlated to the agricultural
occupation in 1963 with a mean
accuracy of 2 metres. Of course, all lot
boundaries can be read under the 1980
horizontal coordinates. The significance
of this exercise is that not only can a
surveyor produce a technically accurate
land parcel boundary based on DD
Sheets and orthophotos, but most
importantly an assessment of accuracy
can also be provided.
SBE
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