# ArcRotateCamera collision behaviour **URL:** \ **Category:** Bugs\ **Tags:** camera\ **Created:** [September 21, 2021, 9:41pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995 "2021-09-21T21:41:39Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![GeraldoOfTheRiviera](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/geraldooftheriviera/32/20993_2.png) [@GeraldoOfTheRiviera](https://forum.babylonjs.com/u/GeraldoOfTheRiviera)\ **Post date:** [September 21, 2021, 9:41pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/1 "2021-09-21T21:41:39Z")
Hi everyone, not sure if this is a bug or not, but here it goes: When defining an ArcRotateCamera, if there is a collision at the initial position, and we try to re-position the camera to avoid this collision, the radius value seems to be ignored. I’ve made a playground with an example: [https://www.babylonjs-playground.com/#A9PJE6#3](https://www.babylonjs-playground.com/#A9PJE6#3) Locally I was able to fix this by calling computeWorldMatrix() right after calling .setTarget(). However, in the playground example above, this doesn’t seem to fix things. Any thoughts? ---
**Author:** ![sebavan](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/sebavan/32/57_2.png) [@sebavan](https://forum.babylonjs.com/u/sebavan)\ **Post date:** [September 21, 2021, 9:55pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/2 "2021-09-21T21:55:12Z")
Adding @PolygonalSun and @RaananW as they both worked on similar topics recently. ---
**Author:** ![PolygonalSun](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/polygonalsun/32/2704_2.png) [@PolygonalSun](https://forum.babylonjs.com/u/PolygonalSun)\ **Post date:** [September 22, 2021, 9:22pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/3 "2021-09-22T21:22:56Z")
Hey @GeraldoOfTheRiviera, just out of curiosity, what version of Babylon.js are you running locally? ---
**Author:** ![GeraldoOfTheRiviera](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/geraldooftheriviera/32/20993_2.png) [@GeraldoOfTheRiviera](https://forum.babylonjs.com/u/GeraldoOfTheRiviera)\ **Post date:** [September 22, 2021, 10:06pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/4 "2021-09-22T22:06:25Z")
Locally, I’m running babylonjs version 4.2.0. I should clarify, locally my issue is the same as in the playground (radius not being respect), however my setup is slightly different: I’m using an upperRadiusLimit. Here’s what I’m thinking: when I do a computeWorldMatrix() right after my .setTarget(), babylonjs detects a collision, sets a new radius, which is above the one I set for upperRadiusLimit. So when the \_checkLimits function of the ArcRotateCamera is called, the camera radius is set to upperRadiusLimit, and the camera is now in a position where no collision is happening. And then, when I set the new radius, I get the correct radius value (because now the camera isn’t colliding with anything). Or something like that 🤔 If I don’t call computeWorldMatrix() right after .setTarget(), I’m guessing babylonjs detects a collision, this collision sets a new radius value, and babylonjs ignores the values I set for the camera’s radius (and possibly alpha and beta as well). My final solution was: after doing the .setTarget(), setting alpha, beta, radius, I did the following: ```auto arcRotateCamera.checkCollisions = false; arcRotateCamera.computeWorldMatrix(); arcRotateCamera.checkCollisions = true; ``` This way I know collisions won’t affect the position I just set for my camera. ---
**Author:** ![PolygonalSun](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/polygonalsun/32/2704_2.png) [@PolygonalSun](https://forum.babylonjs.com/u/PolygonalSun)\ **Post date:** [September 24, 2021, 6:38pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/5 "2021-09-24T18:38:32Z")
So here’s what I’m seeing. It looks like it’s first adjusting the radius to 1 without updating position. Next, it handles the active collision with the `sphereThatCollidesWithCamera` object, which _would_ modify its radius as it shoves the camera to a valid position (min modified distance should be something like sphere radius [2.5] + cam collision radius [3]). Finally, it would update the camera’s position, with respect to the given radius and current target (still 0,0,0). In the PG, I didn’t see that upperRadiusLimit was set and when I tried setting it myself, it worked as intended. I don’t know that I’m seeing a bug here, per se. ---
**Author:** ![GeraldoOfTheRiviera](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/geraldooftheriviera/32/20993_2.png) [@GeraldoOfTheRiviera](https://forum.babylonjs.com/u/GeraldoOfTheRiviera)\ **Post date:** [September 24, 2021, 9:19pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/6 "2021-09-24T21:19:08Z")
Thanks for the reply! What you’re saying makes sense. > It looks like it’s first adjusting the radius to 1 without updating position. Next, it handles the active collision with the `sphereThatCollidesWithCamera` object Personally, it’s not obvious to me that there would be a collision in the first place, since I just set a new target and radius to avoid said collision. While we’re at it, if we do something like: `cam.setTarget(newTarget);` followed by a cam.getTarget(), we will not get a vector with the newTarget we just set. Does this make sense 🤔? PG: > **[Babylon.js Playground](https://www.babylonjs-playground.com/#A9PJE6%234)** > > Babylon.js playground is a live editor for Babylon.js WebGL 3D scenes ---
**Author:** ![sebavan](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/sebavan/32/57_2.png) [@sebavan](https://forum.babylonjs.com/u/sebavan)\ **Post date:** [September 24, 2021, 9:39pm UTC](https://forum.babylonjs.com/t/arcrotatecamera-collision-behaviour/23995/7 "2021-09-24T21:39:48Z")
Yup I will fix the getTarget in the next nightly