C. Reducing layout time
Visual Graph was designed to explore large graphs that
consist of many hundreds of thousands of elements.
However, the layout of large graphs may require
considerable time. Thus, there are two main ways to speed
up the layout algorithm: multi-aspect layout of graph and
control of layout algorithms.
The first way in visualizing a large graph is aimed at
avoiding computing the layout of parts of the graph that are
currently not of interest. Interactive exploring of graph is
based on step by step construction of so-called multi-aspect
layout of graph being a set of drawings of some subgraphs
(fragments) of the graph. For presentation of multi-aspects
layout a set of windows which includes a separate window
for visualization of each considered subgraph is used. At
each step of the construction a layout algorithm is applied to
a subgraph being interested to user at this step. To indicate
the interested subgraph the user can select its elements in the
active window or in the navigator (see below). The user can
also define some condition in the filter or in the search panel
(see below). Then the condition will be used for searching of
graph elements which will form the interested subgraph. The
search can be performed both locally (in some part of graph,
e.g. through a subgraph presented in the active window) or
globally (around the entire graph). Multi-aspect drawing of
graph models makes every visible part of the graph smaller,
thus enabling the layout to be calculated faster and the
quality of the layout to be improved.
In order to further reduce layout time, it is possible to
control the layout algorithms, e.g. some layout phases can be
omitted or the maximum number of iterations of some layout
phases can be limited. However, this usually decreases the
quality of the layout. The user can improve the layout by
hand, e.g. by moving of nodes or changing of their sizes or
forms.