Geoscience Reference
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freely in 360 in the steepest slope). While, the data used in this testing method is
the contour and river tributary data, which had been digitised from topographic
map. A Triangulated Irregular Network (TIN) will then be created from the
contour data using ArcGIS software. The TIN surface model is the best raster
surface to model the terrain slope and aspect of the study area that combined with
the river tributary and to create a model the water flow direction.
4 Implementation and Result
The result of this comparison method can be categorised into two. These are based
on the implementation categorised by the data sources, which are SRTM and
Topographic map (secondary data) and ASTER data.
4.1 SRTM Result (Overlay with TIN Surface)
There are three main comparison aspects used to be observed in this SRTM data.
All of them show that D16 algorithm produces much better results than D8
algorithm result. The aspects are:
i.
Accuracy (divergence in ridge area and smoother flow direction model and
less conflict occur)
ii.
Generalisation result
iii.
Edge reliability
4.1.1 Accuracy
Figure
10
a and b clearly shows that D16 can produce more accurate result (sink and
stagnant) based on the TIN surface, higher divergence in hilly area (purple colour
indicated eight additional flow direction options) and able to produce a smooth
water flow direction model compared to D8 algorithm.
4.1.2 Generalization
Besides that, D16 algorithm is capable of generating a better generalisation result
when dealing with bigger pixel size. There are two set of resolution used in this
testing method, a resampled of 30 m resolution and 120 m resolution SRTM data
samples in order to verify which algorithm will produce better generalisation
result. Figures
11
and
12
are the result of D16 algorithm before and after
