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## A* turning and unit direction

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### #1PantherBoy  Members

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Posted 17 July 2012 - 09:38 PM

Hello all,

I'm currently spending some time trying to improve my pathfinding library and was looking for some ideas on how to deal with direction of units and their turn radius.

For example if a unit had its back to the target, a straight line path wouldn't be suitable as returned by A* (assuming no clear path between unit and target) as the unit would have to rotate around, and the turn radius could potentially make it follow a path that touches grid cells that where not in the original calculated clear path and over cells has a blocking obstacle.

My original thinking was to factor the direction cost into the heuristic function of the A* algorithm but its getting pretty messy and not very reliable so I thought id ask if others have implemented anything similar, thinks this is the wrong approach and has better ideas or even can point me to any helpful papers/articles.

Thanks!

### #2PantherBoy  Members

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Posted 17 July 2012 - 09:43 PM

Sorry I'm not sure how but I double posted by accident, the other double post has now been deleted

Edited by PantherBoy, 20 July 2012 - 04:05 PM.

### #3snowmanZOMG  Members

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Posted 21 July 2012 - 10:01 PM

I have also been investigating various pathfinding solutions that take into account a turn radius and agent orientation. The most useful article I've seen so far on this matter is http://www.gamasutra...pathfinding.php where they essentially make the orientation information a part of their search state space and rule out certain tiles based on the given turning radius during the search.

It's a rather old article, but I think lots of the information there is still relevant. There's also a presentation floating around on aigamedev about some pathing goodness from Company of Heroes, but if I recall, that presentation is a little light on details with regard to their vehicular movement.

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Posted 22 July 2012 - 11:46 PM

The CoH one was done by Chris Jurney. There's a good article on it in AI Game Programming Wisdom 4.
Dave Mark - President and Lead Designer of Intrinsic Algorithm LLC

Professional consultant on game AI, mathematical modeling, simulation modeling
Co-advisor of the GDC AI Summit
Co-founder of the AI Game Programmers Guild
Author of the book, Behavioral Mathematics for Game AI

Blogs I write:
IA News - What's happening at IA | IA on AI - AI news and notes | Post-Play'em - Observations on AI of games I play

"Reducing the world to mathematical equations!"

### #5PantherBoy  Members

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Posted 24 July 2012 - 07:32 PM

Thanks snowmanZOMG and IADaveMark, that Chris Jurney article seems very interesting and looks like it discusses exactly what I was after. The bad news is the book is out of print and used copies seem to be retailing upwards of $400 on amazon . The demand for that book must be very high, wish there was an ebook version I could buy. I'm going to have to try and find someone who has it and can lend it me ### #6GlenDC Members 549 Like 0Likes Like Posted 25 July 2012 - 05:07 AM You can still find the book on the world wide web. If you don't wanna pay because your a poor student or don't have the money for it for other reasons than you can always download it. This is not wrong in my opinion to do, it's just like sharing books, like they do with small books in the metro stations Oh, and thank you snowmanZOMG for your shared information! Edit: Damnit can't find a correct version of the ebook version. Does anyone have a working ebook version of it available online ? Edited by GlenDC, 25 July 2012 - 07:05 AM. ### #7IADaveMark Moderators 3524 Like 1Likes Like Posted 25 July 2012 - 08:45 AM The publisher said they are working on a Kindle version at the moment. Trust me, hilarity ensued when the bots bid the price up to$400.
Dave Mark - President and Lead Designer of Intrinsic Algorithm LLC

Professional consultant on game AI, mathematical modeling, simulation modeling
Co-advisor of the GDC AI Summit
Co-founder of the AI Game Programmers Guild
Author of the book, Behavioral Mathematics for Game AI

Blogs I write:
IA News - What's happening at IA | IA on AI - AI news and notes | Post-Play'em - Observations on AI of games I play

"Reducing the world to mathematical equations!"

### #8GlenDC  Members

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Posted 25 July 2012 - 09:16 AM

Awesome, than I can read it on my lovely Kindle. Thanks IADaveMark for the information. It's pretty insane that the price is so high oO

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