7 research outputs found
Upward Planar Morphs
We prove that, given two topologically-equivalent upward planar straight-line
drawings of an -vertex directed graph , there always exists a morph
between them such that all the intermediate drawings of the morph are upward
planar and straight-line. Such a morph consists of morphing steps if
is a reduced planar -graph, morphing steps if is a planar
-graph, morphing steps if is a reduced upward planar graph, and
morphing steps if is a general upward planar graph. Further, we
show that morphing steps might be necessary for an upward planar
morph between two topologically-equivalent upward planar straight-line drawings
of an -vertex path.Comment: Appears in the Proceedings of the 26th International Symposium on
Graph Drawing and Network Visualization (GD 2018) The current version is the
extended on
Morphing Planar Graphs While Preserving Edge Directions
Two straight-line drawings P,Q of a graph (V,E) are called parallel if, for every edge (u,v) in E, the vector from u to v has the same direction in both P and Q. We study problems of the form: given simple, parallel drawings P,Q does there exist a continuous transformation between them such that intermediate drawings of the transformation remain simple and parallel with P (and Q)? We prove that a transformation can always be found in the case of orthogonal drawings; however, when edges are allowed to be in one of three or more slopes the problem becomes NP-hard
Straight Line Movement in Morphing and Pursuit Evasion
Piece-wise linear structures are widely used to define problems and to represent simplified
solutions in computational geometry. A piece-wise linear structure consists of straight-line
or linear pieces connected together in a continuous geometric environment like 2D or 3D
Euclidean spaces. In this thesis two different problems both with the approach of finding
piece-wise linear solutions in 2D space are defined and studied: straight-line pursuit evasion
and straight-line morphing.
Straight-line pursuit evasion is a geometric version of the famous cops and robbers game
that is defined in this thesis for the first time. The game is played in a simply connected
region in 2D. It is a full information game where the players take turns. The cop’s goal
is to catch the robber. In a turn, each player may move any distance along a straight
line as long as the line segment connecting their current location to the new location is
not blocked by the region’s boundary. We first prove that the cop can always win the
game when the players move on the visibility graph of a simple polygon. We prove this by
showing that the visibility graph of a simple polygon is “dismantlable” (the known class of
cop-win graphs). Polygon visibility graphs are also shown to be 2-dismantlable. Two other
settings of the game are also studied in this thesis: when the players are free to move on
the infinitely many points inside a simple polygon, and inside a splinegon. In both cases
we show that the cop can always win the game. For the case of polygons, the proposed cop
strategy gives an asymptotically tight linear bound on the number of steps the cop needs
to catch the robber. For the case of splinegons, the cop may need a quadratic number of
steps with the proposed strategy, while our best lower bound is linear.
Straight-line morphing is a type of morphing first defined in this thesis that provides a
nice and smooth transformation between straight-line graph drawings in 2D. In straight-
line morphing, each vertex of the graph moves forward along the line segment connecting
its initial position to its final position. The vertex trajectories in straight-line morphing
are very simple, but because the speed of each vertex may vary, straight-line morphs are
more general than the commonly used “linear morphs” where each vertex moves at uniform
speed. We explore the problem of whether an initial planar straight-line drawing of a graph
can be morphed to a final straight-line drawing of the graph using a straight-line morph
that preserves planarity at all times. We prove that this problem is NP-hard even for
the special case where the graph drawing consists of disjoint segments. We then look at
some restricted versions of the straight-line morphing: when only one vertex moves at a
time, when the vertices move one by one to their final positions uninterruptedly, and when
the edges morph one by one to their final configurations in the case of disjoint segments.
Some of the variations are shown to be still NP-complete while some others are solvable
in polynomial time. We conjecture that the class of planar straight-line morphs is as
powerful as the class of planar piece-wise linear straight-line morphs. We also explore
a simpler problem where for each edge the quadrilateral formed by its initial and final
positions together with the trajectories of its two vertices is convex. There is a necessary
condition for this case that we conjecture is also sufficient for paths and cycles