# 3D coordinates behind a camera

**URL:** https://forum.kirupa.com/t/3d-coordinates-behind-a-camera/95416
**Category:** Uncategorized
**Created:** [November 25, 2003, 2:17pm UTC](https://forum.kirupa.com/t/3d-coordinates-behind-a-camera/95416 "2003-11-25T14:17:49Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![YonkersDeluxe](https://avatars.discourse-cdn.com/v4/letter/y/bbe5ce/32.png) [@YonkersDeluxe](https://forum.kirupa.com/u/YonkersDeluxe)
#### Post date: [November 25, 2003, 2:17pm UTC](https://forum.kirupa.com/t/3d-coordinates-behind-a-camera/95416/1 "2003-11-25T14:17:49Z")

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Hi,  
I’ve just been playing around with the 3D tutorials, thanks for  
that!

I just have a problem when a point goes _behind_ the camera:  
if point.z \< 0.  
It’s ok if there’s an MC that just becomes invisible - but if I try  
to draw a line to this point with the drawingAPI, the point’s screen  
x/y coordinates are weird.  
I can’t figure out how to modify the scaleRatio to get correct  
values.  
Here’s a code snippet:

var scaleRatio = focalLength/(focalLength + z);

```
screen_x = x * scaleRatio;
screen_y = y * scaleRatio;

```

Hope the problem is clear.

greets, Y