Geoscience Reference
In-Depth Information
(a)
(b)
Legend:
New added directions
Existing directions (D8)
Involved pixel
Not involved pixel
Fig. 9
D16 algorithm approach
3 Developing New D16 Algorithm Framework
The basic structure of the new D16 algorithm is the phase of designing a con-
ceptual model and introduction of new equations, which are derived purposely to
overcome the limitations of the current SFD or D8 algorithm. Figure
8
shows the
overall framework on how the new D16 is being tested with D8 algorithm from
three sources of raster data up to the output phase of accuracy level. Then, any
necessary enhancement will be implemented through the concept and new equa-
tion of D16 algorithm based on the limitation of D8 results.
The input raster data should be in a two dimensional planar surface and for this
study, Rectified Skew Orthomorphic (RSO) Kertau (a local projection system for
west peninsular Malaysia) is used to project the data into a spatial referenced
system. After resampling the raster-based data into a required pixel resolution, it
will then undergo a conversion process to produce a vector-based data in point
form features.
The vector-based data representation is used in this study because users can
easily visualize and detect the flow direction movement as represented by the
arrow, but not in raster-based presentation. The point layer of D8 result is rep-
resented as arrow symbol with different angles based on the D8 concept illustrated
in Fig.
4
. These point features will undergo the process of resampling pixel and
convert to point using ArcGIS software.
On the other hand, D16 algorithm should be converted from point features into
Comma Separated Value (CSV) format with ID, coordinate (X, Y), and height as
the attributes. This CSV file will be the input data for D16 algorithm because this
compiler tool is prepared in Ruby programming language which is not supported
by ArcGIS software.
The study involved a comparison of several approaches by using different
sources of raster data so that the output result of D16 algorithm is valid for almost
all GIS raster data. The concept and formulae of D16, D16 coding for external tool
and method for comparing the algorithms will be discussed in this section.
