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### #Actualslicer4ever

Posted 14 October 2012 - 03:26 AM

Hi everyone. I'm facing some issues while implementing the steering behaviors such as wall or obstacle avoidance. I share these issues with you as some questions and hope you could help me.

1 - Why do we need to use wall or obstacle avoidance at all when we use A* search algorithm as we know that it ignores obstacle nodes in the search.

2 - the implementation of obstacle avoidance I've accomplished is the one explained in the book Programming Game AI by Examples which use steering behaviors for a 2D space. Shoud I take advantages of raycast or collision detection instead for implemening such a behavior in a 3D space or that one is enough?

3 - Any obstacle avoidance behavior explanation I've seen either in the book or on the Internet assumes that the obstacles are circles. what about for rectangular obstacles? Is there any differences in the calculations?

1. A* is a great pathing system for a known environment, if you can design your system in a way that A* is fine enough for avoidance systems, then by all means, solely use A*.

however, sometimes A* can only be used for generating an overview of the path to take, but doesn't describe how the object should reach a node, particularly for highly dynamic scenes, where an fixed A* grid is simply not precise enough. At the end of the day, it's upto you to choose how your objects well get from point A to point B.

2. I can not comment, as i've not read the book.

3. a circle is used because that is simply the shape which you will always end up with. since obstacle avoidance relies on generating one(or two) points that allow's your avoiding obstacle to avoid the other object, you've successfully generated a circle(which is a center point, and a radius, the radius is the distance from the center, to this arbitrary point.)

since any object well have to be decomposed into a circle to be successfully avoided, then it's simpler to only work with circle's when presenting the idea.

but what if we have a rectamgular cube with a long length and short width in the middle of the room? should we consider it as a wall? in this case we can't determine any circle since the length and the width are not the same size.

you can always get a circle from any shape, simply take the furthest point from the center, and you have a circle which encapsulates the object.

does that circle accurately bound the entire object? not exactly, does the collision avoidance system work decent enough? that's up to you. so if you want a better refined circle, you could construct an eclipse, which can be used pretty decently with only a few modifications to the general collision avoidance algorithm

### #1slicer4ever

Posted 14 October 2012 - 03:24 AM

Hi everyone. I'm facing some issues while implementing the steering behaviors such as wall or obstacle avoidance. I share these issues with you as some questions and hope you could help me.

1 - Why do we need to use wall or obstacle avoidance at all when we use A* search algorithm as we know that it ignores obstacle nodes in the search.

2 - the implementation of obstacle avoidance I've accomplished is the one explained in the book Programming Game AI by Examples which use steering behaviors for a 2D space. Shoud I take advantages of raycast or collision detection instead for implemening such a behavior in a 3D space or that one is enough?

3 - Any obstacle avoidance behavior explanation I've seen either in the book or on the Internet assumes that the obstacles are circles. what about for rectangular obstacles? Is there any differences in the calculations?

1. A* is a great pathing system for a known environment, if you can design your system in a way that A* is fine enough for avoidance systems, then by all means, solely use A*.

however, sometimes A* can only be used for generating an overview of the path to take, but doesn't describe how the object should reach a node, particularly for highly dynamic scenes, where an fixed A* grid is simply not precise enough. At the end of the day, it's upto you to choose how your objects well get from point A to point B.

2. I can not comment, as i've not read the book.

3. a circle is used because that is simply the shape which you will always end up with. since obstacle avoidance relies on generating one(or two) points that allow's your avoiding obstacle to avoid the other object, you've successfully generated a circle(which is a center point, and a radius, the radius is the distance from the center, to this arbitrary point.)

since any object well have to be decomposed into a circle to be successfully avoided, then it's simpler to only work with circle's when presenting the idea.