<p>Excuse my wording. I will use the picture below to explain what I mean. I want to use the surface normals for each arrow shown like below to draw lines parallel to each plane like the image shown below the first one. Therefore I want to obtain point coordinates given in black dots.</p>
<p>Assuming I have a unit normal (u, v, w) to each plane, how can this be accomplished?</p>
<p><a href="https://i.sstatic.net/gNw3x.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/gNw3x.png" alt="enter image description here" /></a></p>
<p><a href="https://i.sstatic.net/4zPy7.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4zPy7.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2020-11-16T05:48:17.233Z
Normals dont tell how far that plane is. But im sure same ai has a depth estimate too.
joojaa
CC BY-SA 4.0
2020-11-16T05:59:34.917Z
yes i have depth maps. so how can i do that if i have the depth information?
user1696420
CC BY-SA 4.0
2020-11-16T06:14:05.347Z
Depth + knowledge of camera FOV is 3D data
joojaa
CC BY-SA 4.0
2020-11-16T14:45:31.320Z
so in effect the surface normal has no use in this application?
user1696420
CC BY-SA 4.0
2020-11-16T15:32:49.373Z
Well, it can make triangulation easier. Its also useful for a system to validate the data.
joojaa
CC BY-SA 4.0
2020-11-17T01:12:30.807Z
You still gonna need the normal after you find a point on the plane through the depth map, I think. How else you gonna find the black point then?
gallickgunner
CC BY-SA 4.0
2020-11-17T01:37:59.410Z
@gallickgunner I actually don't understand why normal + origin (where normal sticks out of) is not enough. I am trying to build a plane (a rectangular region) which I can use for homography. I can visually select four points manually, but I want to automate this process via normals and if necessary, depth maps. Do you have any conceptual advice I can try to work on?
user1696420
CC BY-SA 4.0
2020-11-17T02:04:46.483Z
Well I'm not familiar with homography. But if it's only about picking four points on a plane you need a normal and a point on the plane. You can get a point through the depth map (search for recalculating world space position from depth map values) and you already have the normal. Now all you need to do is find a vector parallel to the plane. Just cross the normal with any vector that's not parallel to the normal and you'll get that. Now add this vector with any length to the point vector (one gotten through depth map) and you have different points on the plane.
gallickgunner
<projections>
Can surface normal be used for obtaining points on a plane?
user1696420
# Can surface normal be used for obtaining points on a plane?

(Asked by: username_0 on 2020-11-16)

Excuse my wording. I will use the picture below to explain what I mean. I want to use the surface normals for each arrow shown like below to draw lines parallel to each plane like the image shown below the first one. Therefore I want to obtain point coordinates given in black dots.

Assuming I have a unit normal (u, v, w) to each plane, how can this be accomplished?

[![enter image description here](https://i.sstatic.net/gNw3x.png)](https://i.sstatic.net/gNw3x.png)

[![enter image description here](https://i.sstatic.net/4zPy7.png)](https://i.sstatic.net/4zPy7.png)

**Tags:** projections

> **Comments:**
> **username_1**: Normals dont tell how far that plane is. But im sure same ai has a depth estimate too.  
> **username_0**: yes i have depth maps. so how can i do that if i have the depth information?  
> **username_1**: Depth + knowledge of camera FOV is 3D data  
> **username_0**: so in effect the surface normal has no use in this application?  
> **username_1**: Well, it can make triangulation easier. Its also useful for a system to validate the data.  
> **username_2**: You still gonna need the normal after you find a point on the plane through the depth map, I think. How else you gonna find the black point then?  
> **username_0**: @username_2 I actually don't understand why normal + origin (where normal sticks out of) is not enough. I am trying to build a plane (a rectangular region) which I can use for homography. I can visually select four points manually, but I want to automate this process via normals and if necessary, depth maps. Do you have any conceptual advice I can try to work on?  
> **username_2**: Well I'm not familiar with homography. But if it's only about picking four points on a plane you need a normal and a point on the plane. You can get a point through the depth map (search for recalculating world space position from depth map values) and you already have the normal. Now all you need to do is find a vector parallel to the plane. Just cross the normal with any vector that's not parallel to the normal and you'll get that. Now add this vector with any length to the point vector (one gotten through depth map) and you have different points on the plane.  

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## 0 answers

