Catch Me If You Can
Group 20
B94902027鍾政達
B94902067陳建男
B94902080何雨帆
Rules of the Game
Two agents playing human and ghost
respectively
The ghost agent’s goal is to catch the
human agent
The human agent’s goal is to avoid being
caught by the ghost in a round
The Environment
The map will be an 39x39 bitmap input
Human is in the lower right corner at the
beginning
Ghost is in the upper left corner at the
beginning
The Strategy: Human (Ver.1)
Construct a heuristic to define the
“degree of danger” of each node
When ghost appears, plan an escaping
route base on the heuristic
After we reached the goal, if the ghost is
not in sight, keep rotating and scan
State Diagram (Ver.1)
Rotating Scan
Route Planning
Ghost Insight
Goal Reached
Walking
The Heuristic Function
Heuristic(x, y)
= DegreeOfDanger(x, y)
= Combine((DistanceToGhost(x, y),
Compact (x, y))
Definition of Compactness
Check the 7x7 array
centered by (x, y)
Sum up the number
of those bits that are
black (obstacle)
Map of Compactness
Combination of Distance &
Compactness
Naïve way
Danger = Compact – k * Distance
Our way
400 – Compact Compact
Danger = ─────── + ─────
10 * Distance
4
What is this!?
Why Bother?
Compact + Near
Empty + Near
Compact + Far
Empty + Far
＊The ranges between
these four statuses
should equal to each
other
Refinement 1: Rotating State
Full speed of ghost & human are similar
 Turning becomes a deterministic point
 Human should avoid turning as much as
it can
 The “Rotating Scan” state becomes a
vulnerable point!
Refinement 2: Keep Walking
The sight of pioneer 3DX robot is narrow
 It is likely that the ghost is chasing us but
we dose not notice
 Staying at the same point do no good
 Keep walking!
Moving Method
Avoid Collision
Adjust Velocity
No Rotate + Keep Walking = Drift
Drift: No Rotate
Search 10 nodes away
from our current position
base on the direction on
the map
Check if there are any
obsticles between the
node and us
Pick the farrest node as
the “short goal” and go
staight toward it
Drift: No Rotate
Why 10 Nodes?
Drift: Keep Walking
Update the short goal
by watch dog
(we may never reach
the short goal)
Change the speed of
both wheels to adjust
the direction while
forwarding
State Diagram (Ver.2)
Build up the
Compactness
Map
Build up the
Ghost Map
Plan Route
Build up the
NextGoal Map
On Its Way
To the Goal
Ghost Insight
Goal Reached
Refinement 3: Ghost Insight
If the ghost is too close to us
 Rotate becomes time wasting
 Two kinds of “Ghost Insight”: Near & Far
 Changes the direction while moving!
Ghost Insight & Near
Dash Route 1
Dash Route 2
State Diagram (Final Version)
Build up the
CompactMap
Build up the
Ghost Map
Plan Route
Build up the
NextGoalMap
On Its Way
To the Goal
Dash
Ghost: Far
Goal Reached
Ghost: Near
Ghost Insight
The End
Thanks for your attention