# Find the Collision Point: HOW?

• One massively long rectangle as the ground. It's VERY long.

A ball lands on it, and I want to play a puff of smoke particle animation at the landing point.

How do I find that contact point?

• @Deeeds The Collided behaviour can output the coordinates of the collision point. I’ve never used it, but I’m pretty sure you should be able to use it. Best way might be to spawn a temporary particle object at the point.

• @Aidan-Oxley how/where do I get those coordinates?

• @Aidan-Oxley Further, how do I then position a particle system at that point? It seems that particle systems don't have positional settings, only anchor settings, so they can't exist in the world without a parent object. Which is a little strange.

• @Deeeds it’s the output for the collide behavior. However it is relative to the object so to make it world coordinates you would need to do a little math. What you could do is have one of the colliding objects play the particle(with behavior) and then the output would be all you’d need. Or you could have a particle object and then you should be able to set its position to the collide point (converted to world coordinates).

• @iTap-Development Argh, I see. So particles can be dragged into the world... and then.... oh... starting them after that is a nightmare.

I think I've figured this out.

Create a dummy (invisible) object. Move it to the point of the collision, activate a particle system on that dummy object. This is the collision point.

• @iTap-Development btw, that collision info, from my testing, looks to be in world units already. I think. I have the ground object getting the collision information, putting the dummy object at that location, and then starting the particles "on" that dummy object.

• @Deeeds but why not have one of the colliding objects play it, with an anchor of the the collide point? More efficient.

• @iTap-Development How do you create an anchor at the collide point? The anchor point is in percentages, the collision point is in units.

• @iTap-Development more to the point, why should I need to do such ridiculous maths to find and then USE a location of a collision? If collision points aren't the single most important piece of information a physics library ever produces, they're second.

• @Deeeds I’m confused...what’s the difference between collide pout and collision point?

• @iTap-Development Nothing. Where a collision happens is where some things have collided.

• @Deeeds but before you said one was percentage and one was units?

• @iTap-Development From memory, Chipmunk produces collision objects that report the location of collisions on the involved objects and world space. I'm not sure why something like this hasn't been surfaced in a welcoming, enjoyable, endearing and empowering way, regardless of how Chipmunk handles collisions.

• @iTap-Development anchor points are in percentages.

• @iTap-Development sorry, typo.

• This post is deleted!

• @Deeeds just checked, it looks like output is world units. So you would have to convert for play particle. That sucks.

• @iTap-Development I don't understand what you're saying. World Units are the useful ones, I thought. Given that, I can move an object to that point and do something with it.

Without the edge information and absolute coordinates on that edge (of an object) relative information is of little to no use. That I can think of. Polygon shapes in hyperPad have too many problems anyways... no way to snap lines to angles, etc.

• @Deeeds ok...I guess I’m confuse too🤷‍♂️