Drawing in radial layout mode and free layout mode can
be adjusted according to the aspect ratio of the drawing area. To
balance the height and depth of the drawing, free layout mode can
also use tip-over alignment.
Tip-over alignment can be specified explicitly for individual
nodes. The Tree Layout algorithm also has layout modes that automatically
use tip-over alignment when needed.
The tip-over layout modes work as follows:
Several trial layouts are performed in free layout mode.
For each trial, tip-over alignment is set for certain
individual nodes, while the specified alignment of all other nodes
is preserved.
The algorithm picks the trial layout that best fits the
specified aspect ratio of the drawing area.
Use the method setAspectRatio, whose value is a Number.
The tip-over modes are slightly more time-consuming than
the other layout modes.
For large trees, it is recommended that you set the allowed
layout time to a high value (for instance, 50 seconds) when using
the tip-over modes.
To set this mode:
Call:
layout.setAllowedTime(50000);
By using this call, you avoid running short of time for
sufficient iterations of the layout algorithm. Because it would be
too time-consuming to check all possibilities of tip-over alignment
use, heuristics exist that check only certain trials according to
the following different strategies shown in the following figure.

Tip-over strategies
Tip leaves over
To use this tip-over strategy, set the layout mode as
follows:
treeLayout.setLayoutMode(ibm_ilog.graphlayout.tree.TreeLayout.TIP_LEAVES_OVER);
The heuristic first tries the layout without any additional
tip-over options. Then it tries to tip over the leaves, then the leaves
and their parents, then additionally the parents of these parents,
and so on. As a result, the nodes closest to the root use normal alignment
and the nodes closest to the leaves use tip-over alignment.
Tip roots over
To use this tip-over strategy, set the layout mode as
follows:
treeLayout.setLayoutMode(ibm_ilog.graphlayout.tree.TreeLayout.TIP_ROOTS_OVER);
The heuristic first tries the layout without any additional
tip-over options. Then it tries to tip over the root node, then the
root and its child nodes, then additionally the child nodes of these
child nodes, and so on. As a result, the nodes closer to the leaves
use normal alignment and the nodes closer to the root use tip-over
alignment.
Tip roots and leaves over
To use this tip-over strategy, set the layout mode as
follows:
treeLayout.setLayoutMode(ibm_ilog.graphlayout.tree.TreeLayout.TIP_ROOTS_AND_LEAVES_OVER);
The heuristic first tries the layout without any additional
tip-over options. Then it tries to tip over the root node and the
leaves simultaneously; then the root and its child nodes, and the
leaves and its parent; then additionally the child nodes of these
child nodes and the parents of these parents, and so on. The result
is that the nodes in the middle of the tree use normal alignment and
the nodes closest to the root or leaves use the tip-over alignment.
This strategy is the slowest, because it includes all
trials of the strategy tip leaves
over as well as all trials of the strategy tip roots over.
Tip over fast
The fast tip-over provides a compromise between all other
strategies. The heuristic tries a small selection of the other strategies,
not all possibilities. Therefore, it is the fastest strategy for large
graphs.
To use this strategy, set the layout mode as follows:
treeLayout.setLayoutMode(ibm_ilog.graphlayout.tree.TreeLayout.TIP_OVER);
It is possible that all four strategies yield the same
result because the strategies are not disjoint; that is, certain trials
are performed in all four strategies. In addition, the tip-over modes
do not necessarily produce the optimal layout that gives the best
possible fit to the aspect ratio. The reason is that some unusual
configurations of tip-over alignment are never tried because doing
so would cause the running time to be too high.