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Roland_Y

Member Since 27 May 2012
Offline Last Active Mar 02 2014 08:08 AM

Topics I've Started

Pathfinding with units of different sizes

08 April 2013 - 01:25 PM

Hi all,

 

I am actually working on a general purpose pathfinding library (written in Lua, find it here), mostly oriented for grid-based maps. I was looking for ways to integrate support for pathfinding with units of different sizes.

Actually, I am working with the assumption that all units are square (i.e. their widths and heights in tile units are the same).

 

I came across a very comprehensive article (about Annotated A-star and true clearance values for pathfinding). I succeeded in implementing it, and got it working with a wide range of search algorithms (A-star, Theta*, Dijkstra, DFS, Breadth-first search and Jump Point Search).

 

Yet, there are some small details of implementation I think I am still missing.

First of all, when an agent is 2x2 sized (i.e it occupies 4 tiles on the grid map), what tile can be assumed to be the agent position ? On the same page, clearance based pathfinding will fail in some cases. Let's consider the following map, where 0's are passable tiles, 1's are obstacles and 'x' matches walkable goal to be reached. Let's assume we are pathing with a 2x2 sized unit:

 

  • Situation 1

 

00000000
00111100
001x0100
00100100  
00000000

  • Situation 2

00000000
00111100
0010x100
00100100
00000000

 

For situation 1, tile 4,3 has a clearance value of 2. No problem here. But, for situation 2, tile 5,3 has a clearance value is 1.

So depending on how the agent position is considered, pathfinding will fail while obviously, for each of the two situation, the agent could reasonably fit into the dead-end space.

 

Another scenario, with the same 2x2 sized agent:

 

0000000x
0000000x
0000000x
0000000x
xxxxxxxx

 

Well, assume all tiles are walkable here, so no obstacles. We want the object to reach any of the tile marked 'x', on the rightmost or bottom-most border. Each of these tiles have a clearance of 1, so annotated pathfinding wil obviously fail here again...Well, depending on how the agent's position is taken.

 

How should I work around this issue?

 

Best regards,

Roland.


Pathfinding : Jump Point Search - Straight Moves vs Diagonal Moves

27 May 2012 - 02:58 AM

Hi community,
I'm new here, so please be gentle... :)


Planning working on a 2D RTS, I tried to learn how Astar works.
Indeed, I found articles explaining how Astar could be optimized coupling it with binary heaps,
and algorithms taking advantages of Path symmetry, like Jump Poin Search algorithm.
I made my own implementation and it happened to run fine.
I even made some benchmarks tests with maps from MovingAI Labs.

Yet there is a problem. Everything runs fine when diagonal moves are allowed.
When disabled, no path is returned when the case it involves a diagonal move....
It may be linked to the way I implemented it, then I'm all asking...
In general, how would you oblige the algorithm (JPS) to search for path involving only straight moves (not diagonals moves) to reach a goal ?
Thanks in advance!

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