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What are the differences between ray tracing and ray casting? Ray casting technology uses raster images with no ray splitting or reflections. Ray tracing, on the other hand, typically refers to that technology that uses the physical properties of light.
Are you confused with the technicalities? Well, here are some major differences between ray casting and ray tracing compiled for your better and easy understanding. Read on.
- Ray casting is a process to create and calculate rays depending on the object it hits but ray tracing is a process to create them depending on the reflection or refraction path of the ray.
- Ray casting is a collection of casted and tracked rays based on geometric constraints but ray tracing is done individually.
- Ray casting is not recursive but ray tracing is recursive in nature and is therefore quite slow.
- Though the ray casting process is faster than ray tracing, it is not as precise as ray tracing which uses different algorithms and formulas.
The 11 Differences Between Ray Tracing and Ray Casting
1. Creation and Calculation
Fundamentally and non-technically, ray casting involves a process whereby rays are created and calculated on the basis of what object it hits, or if anything it hits at all.
On the other hand, ray tracing involves a process where the rays are created and its path is traced on the basis of its reflection or refraction after hitting an object and all through the scene.
This process allows determining the type of light that may arrive at the source from the other way.
In ray casting, the rays are cast and tracked as a collection based on particular geometric constraints.
For example, for a 320 x 200 display resolution only 320 rays are traced in ray casting because there are 320 horizontal pixel resolutions in the display.
On the other hand, in the ray tracing technique every ray is traced individually so that every pixel or point on the display can be traced by a single ray.
For example, for a 320 x 200 display resolution, a total of 320 x 200 = 64,000 rays are traced by the ray tracer.
The ray casting process is not recursive in nature because the engine stops when a ray hits an object for the first time.
It then uses an ordinary lighting model to find out the incoming illumination empirically. Therefore, in essence, ray casting is ray tracing but without any ‘child rays.’
On the other hand, ray tracing is recursive, which is why it is slow. This means that recursive propagation is created for several other rays by a specific ray shot out from the viewing position through the viewing plane.
It helps in determining the illumination of the point that has been intersected primarily.
In the ray casting method what is hit by a single ray segment is found out. Therefore, in simple words it is nothing but searching the hit incrementally all along the ray from the eye.
On the other hand, ray tracing is a process where numerous ray casts for each pixel are required. Typically, it is calculated by using an equation directly.
5. Formula Precision
The formula used in ray casting is not exact in most of the cases.
On the other hand, the formula or algorithms used in the ray tracing technique are pretty accurate in most of the cases.
The ray casting process is much faster in comparison to ray tracing since it needs to trace less number of rays. This makes it very useful for real time processes.
On the other hand, the ray tracing process is much slower in comparison and is therefore not suitable for real time processes.
According to the above example, it is about 200 times slower than the ray casting process.
The ray casting process can be carried out only on simple geometric shapes due to its one or more geometric limitations.
On the other hand, ray tracing techniques can be followed to render images of almost any shape.
In the ray casting process, the images that are finally rendered are not stored on the disk.
Typically, it stores only the map and as for the corresponding images to those maps, these are normally produced on the fly.
On the other hand, all the images that are rendered in the ray tracing process are typically stored on the disk and are loaded as and when these are required.
As of now, there is not too much hardware available that is fast enough to render the images after ray tracing on the fly.
9. Number of Rays
Usually, in ray casting there is less number of rays to trace due to a few geometric constraints. Typically, this particular technique is actually an implementation of ray tracing with a special purpose.
On the other hand, there are lots more rays to handle in ray tracing that may come from all possible directions and also move in different ways after hitting an object. Therefore, it is a much more complex technique.
10. Secondary Rays
In the ray casting process, no secondary rays are used. This means that these specific features are either not employed or, if they are, it is done by using some other types of algorithms, which probably are more inaccurate.
On the other hand, in the ray tracing process the secondary rays are used. These rays typically help the ray tracer to compute particular shadows, reflection, refraction, and the probable indirect illumination.
11. Quality of Images
The resulting images in the ray casting process are not very realistic since it does not take reflection and refraction of light into account. Therefore, the images are often displayed in blocks.
On the other hand, the images rendered via ray tracing technique are very realistic, often too realistic with shadows and reflection clearly displayed.
Which is Better – Ray Tracing or Ray Casting?
Ray casting and ray tracing are two different technologies that are used for one particular purpose – for rendering better images.
However, with better and more precise algorithms used, ray tracing happens to have a specific edge over ray casting, making it a significantly better, though complex, technology.
If you are wondering how that is, the following facts and points discussed will make things clearer to you.
Typically, ray casting is a process that is exactly the opposite of rasterization. Here, everything technically starts from the virtual screen rather than the 3D shapes or vectors.
A ray is projected starting from a pixel of the screen till it intersects with a triangle.
The cost is however related directly with the number of pixels of the screen.
It is considered to be really a cheap way to find the first triangle that is intersected by a ray but, in the end, it turns out to be more expensive than rasterization.
By design ray casting will ignore all those specific triangles that are not within the field of view.
Still, it can be used to continue after the ray hits the first triangle on its way in order to take a tiny part of the color of the next triangle.
This helps in creating a clear and less jagged border for a triangle and handles transparency more accurately.
On the other hand, ray tracing, though it follows the same concept, continues with the reflection of the ray after it hits a triangle and moves into a different direction.
A number of reflections can be considered in this process and it is this number that determines the ‘depth’ of ray tracing.
The calculations are exact in terms of color pixels because it is computed on the basis of the light source and the reflected rays along with all the polygons it reflects off in order to get to a particular screen pixel.
The images rendered by ray tracing are more realistic.
It looks just the same as the things that you see around you in your room which are all illuminated by a stream of light that is reflected off their surfaces enabling you to see them.
If you follow the path of the beam of light from your eye backwards to the objects and further to the light source, it is said that you are doing ray tracing.
Therefore, ray tracing is essentially an eye oriented process which involves following a stream of light, in pixels, to find out the objects that fall on its way.
Ray tracing is also a process that follows a pixel from a fixed point and reproduces how it would react when it hits an object.
When you compare the ray tracing process with rasterization you will find that it is quite different, if not hard to implement in real time.
This is because it does not start and end with tracing and processing a single ray.
It also involves tracing and processing its path after it hits an object and reflects thereof.
Now, after reflecting, the single ray, depending on the surface of the object it hits, can turn into ten rays which can further turn into hundreds, thousands and so on.
It may increase exponentially and calculating all of them is very difficult and time consuming.
However, in the case of video games, where there is only a miniscule fraction of a second of time available to render the images, the ray tracing process is hard to implement because you will need 500-Hz hardware for that.
And, as of now, there aren’t many of them available, as said earlier.
Therefore, it is quite natural that real time graphics in most of the cases have to rely on rasterization.
Do not compare this with what the movie makers do because they typically do the graphics works mostly offline and therefore can take their own sweet time to create and render one single frame.
Oftentimes, based on the definitions of both, ray tracing and ray casting may seem very much the same.
In fact, in lots of books and articles, these two terms are often used interchangeably.
However, from the point of view of a game programmer, these two are different and ray casting, in particular, is considered to be a special subclass of ray tracing.
To a game programmer, ray casting is a process which calculates the points of intersections of light with a triangle.
And as for ray tracing, they think it to be a special rendering process that uses ray casting for rendering a 3D object by calculating shadows and reflections along with it.
To them, ray tracing is usually too much a slow process that hinders game development.
Considering the facts above, it can be concluded that ray tracing, very much like ray casting, traces imaginary light rays from the eyes of the viewers to the items in a scene to find out the visibility of the surfaces.
However, ray tracing is better in terms of accuracy and a high level of visual realism while ray casting is a much simpler and faster subclass of ray tracing that involves fewer computing cycles.
In fact, if ray casting involves 10 cycles for rendering a particular image, ray tracing would take thousands of it, and even tens of thousands of cycles for voxel rendering, if done honestly.
As it is evident from this article, ray casting is a specific subclass of ray tracing but both have distinct differences.
Now that you know the differences, you can easily decide whether you would be happy with ray-casted visuals or go for more realistic ray-traced visuals while gaming.