On logical fisheye views, the distance is not calculated wrt.
coordinates but with respect to the structure of the graph.
Distorting and filtering views are possible.
The typical distance is the length of the shortest path from
the focus node [Fu86].
For compound subgraphs, a combined method must be used
taking into account the primitive edges and the nesting structure [No93].
The reason: a node should not be larger (or filtered later) than the frame it
belongs to.
Logical fisheye views have two advantages:
They reflect the structure of the graph,
because a logical fisheye view does not depend on the node
positions.
A graphical fisheye might filter a node that is closely related
to the focus node by the fact that it is accidentally placed far away
from the focus point.
They allow to calculate the layout after the fisheye effect.
Layout calculation becomes the faster the more nodes are filtered away.
Furthermore, the space occupation might be better if the layout
is calculated afterwards.
As disadvantage, logical fisheye views don't have similarities with
optical physics.
Human beings are not used to deal with such effects.
For instance, moving the focus point of a logical fisheye view
might change the graph so much that the layout afterwards cannot
be compared with the layout before.
