# Explanation of Surface Normal?

I know when you raycast, 4 pieces of information are returned, one being the surface normal. Im just wondering what a surface normal is and what I can do with it. I’ve seen stuff on the wiki about reflecting rays using surface normals and I’ve also seen other scripts use them for different things, but I have no idea what it is, what it’s for, or what to do with it.

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I looked around the forums and found another similar forum post that was made back in 2015 that gives an explanation of it. I hope it helps:
https://devforum.roblox.com/t/surface-normal-why-vector3/12654

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On ROBLOX, the Surface Normal returned by the Raycast function is essentially just a Vector that is perpendicular to the tangential surface which the Raycast has hit.

Here is a pretty good visualization of it from Wikipedia: 11 Likes

Does this mean that we can then create another ray which is essentially a reflection of the original ray?

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Still a bit confused, isn’t the surface normal just a point? Like, would there be a significant difference between a surface normal of (3,4,3) and (3,7,3)?

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## What is it?

A surface normal is a vector.

The normal of a surface is a line which points directly outwards, perfectly flat from the surface. It is considered to be an indication of what direction a point on a surface is facing.

So, the surface normal of a flat surface pointing toward the sky would be:

``````Vector3(0, 1, 0)
``````

It’s also important to note that the vector is usually normalised, so the magnitude is set to 1.

## What it’s for

Surface normals are used by the lighting engine to calculate shine. The more similar the surface normal of a surface and the vector to the light emitter are, the more shine is applied. Quick note: I’m not sure if that is exactly what Roblox’s engine does, but it’s how I’ve seen shine calculated in every lighting engine ever, so I guess we can assume it does.

This is the only area which I’ve ever used it. I’ve oversimplified the exact algorithm a bit, so that it doesn’t fill the entire page, but that’s the basics, and it’s a very common use of the surface normal.

## What to do with it

I’ve seen it used for a lot of things, including calculating the bounce of an object, right up to wall bang in an FPS game.

They’re multipurpose, and, with a bit of math, you can use it to do some very cool simulations.

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The surface normal is a vector, which can be imagined as a description of an arrow in 3D space.
In the example given by @jody7777, the arrow is a representation of the vector that is perpendicular (aka normal aka at a 90 degree angle to) the surface at that point. A Vector3 is described as such because it is a vector with 3 components, normally (x, y, z). Now let’s say that the length of the arrow in the above image is 5 units. It is shown to be pointing straight up, in the positive-y direction (if it was pointing straight down, it would be pointing in the negative-y direction).

We can describe this arrow with the vector (0, 5, 0) - it has no unit in the x or z directions, as it is not pointing forwards, backwards, or side-to-side- it is only pointing upwards. Again, if it was pointing straight down we could describe it as (0, -5, 0).

Yes, there would! (3,4,3) can describe an arrow pointing 3 units in the x direction, 4 units in the y direction, and 3 units in the z direction. However (3,7,3) would describe an arrow pointing 3 units in the x direction, 7 units in the y direction, and 3 units in the z direction.

From this we can figure out that the second arrow would point to a location 3 units higher than the first one. We can also figure out that the length (i.e. magnitude) of the arrow (i.e. vector) is greater.

Edit:
It is also worth noting that the Surface Normal returned by the raycast always has a magnitude of 1, which in our analogy means that no matter which direction the arrow is pointing in it will always be exactly one unit long.

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Surface Normal is the direction which a surface faces. The top surface of a non-rotated part will be `Vector3.new(0,1,0)` and the bottom will be `Vector3.new(0,-1,0)`. Basically, this represents the unit vector of the surface, or 1 stud in the direction of the surface.

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Yes, you can calculate the ‘Reflection’ from a ray hitting a surface given you know the initial ray and the surface normal. You can use the law of reflection in order to calculate the reflected ray vector.

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