Geoscience Reference
In-Depth Information
Recursively, every river stemming from a river that has been deleted is de-
leted too. The reconstruction process avoids that a long river course could
stem from a short one: the scoring in fact tends to build courses using the
longest branches (see
Figure 6
).
2.3.5 Dense rivers pruning
The last step of the process is to detect the regions where rivers are too
dense (rivers are too close to each other) and to delete the less important of
them. The algorithm that we developed uses buffers to find which rivers
are too close to others and uses the same scoring procedure explained be-
fore to assess the importance of a river to decide whether to delete it or
not.
A buffer is built around each river course and the percentage
P
of the area
of this buffer that is covered by other buffers is calculated and assigned to
the river course (the percentage is the ratio between covered area and total
area). All the river courses are then decreasingly ordered by the percentage
P
: the higher the value of
P
and the more this river course is close to other
rivers courses. Starting from the highest
P
, the importance of every river
course is evaluated and, if below certain parameters, it is deemed not
important and it is deleted. When a river course is deleted, all the river sec-
tions comprising it are deleted, its buffer is deleted, and the values of
P
of
the neighboring river courses are updated accordingly; the same happens
to every river course stemming from it.
The process continues until the highest value of
P
is below a certain
threshold
Pmax
or there are no more river courses to be deleted over that
threshold (i.e. all the river courses having
P
bigger than the threshold are
deemed too important to be deleted).
