<p>If you want to use the traditional x is towards right and y is up you are used to in math and physics classes. Now if you follow a right handed coordinate space, which is also commonly used. Then the direction of the z follows from the x and y direction.  In this sceme positive z is pointing out from the screen.</p>

<p>Now you can also choose a left handed coordinate system in which case the z is reversed. Its just a matter of choosing which convention you want to use. </p>

<p>Likewise if you choose y to be down, ala traditional windowing math then z is reversed even if you use right hand rule.</p>

<p>None of these conventions are set in stone you can do whatever you want. A bit like you can choose row major or column major matrixes. You just need to know what comvention you follow.</p>

CC BY-SA 4.0
2019-12-09T19:45:18.977Z
2019-12-09T19:53:16.833Z
2019-12-09T19:53:16.833Z
joojaa
<p>I wonder what is the reason that when z increase, the objects appear far away and when z is negative, the object is behind the camera?</p>

CC BY-SA 4.0
2019-12-09T21:15:10.840Z
To answer the title question: it is not.
lightxbulb
<3d><projections><rasterizer>
Why is the z direction away from the screen/viewer?
Voko
# Why is the z direction away from the screen/viewer?

(Asked by: username_0 on 2019-12-09)

I wonder what is the reason that when z increase, the objects appear far away and when z is negative, the object is behind the camera?

**Tags:** 3d, projections, rasterizer

> **Comments:**
> **username_1**: To answer the title question: it is not.  

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## 1 answers

### Answer by username_2 on 2019-12-09. Score: 1

If you want to use the traditional x is towards right and y is up you are used to in math and physics classes. Now if you follow a right handed coordinate space, which is also commonly used. Then the direction of the z follows from the x and y direction. In this sceme positive z is pointing out from the screen.

Now you can also choose a left handed coordinate system in which case the z is reversed. Its just a matter of choosing which convention you want to use.

Likewise if you choose y to be down, ala traditional windowing math then z is reversed even if you use right hand rule.

None of these conventions are set in stone you can do whatever you want. A bit like you can choose row major or column major matrixes. You just need to know what comvention you follow.


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