The first CATIA Hackathon in China attracted a group of car design players. In CATIA Hackathon, each team, with a configuration of "1 mentor + 2 designers + 4 modelers + 1 CATIA expert", was to complete a "Future Driving Experience" design within merely TWO DAYS, during which each team endeavored to advance the design progress and attain the design objective with innovation, quality, and completion. After the previous Team B article, let's take a look at the design concepts and processes of Team A.
Filipe Braganca the mentor, with all Team A members, was brainstorming
The design of Team A is called SEC-X. S stands for Supra, E for Energetic, C for Conversion, and X for Experience; The team asked themselves, what is the core value of mobility in the future, with the accomplishment of autopilot and many more technologies. Their answer was — Break Through: SEC-X has two modes, driving mode and exploring mode. Through the transformation between the two, the attention of the crew will be shifted to bring a breakthrough experience.
SEC-X exterior concept - driving mode
In driving mode, SEC-X lowers the rear down, switches to manual driving mode, gets a better aerodynamic shape, and also enables the driver to drive in a racer's posture.
SEC-X exterior concept - exploring mode
In the exploring mode, SEC-X rises the rear up, switches to the autopilot mode, provides the driver better visibility so that he/she can browse the information on the roof of the car, and enjoy the scenery along the way.
SEC-X interior concept
In the whole design process, each application module of 3DEXPERIENCE empowers designers and digital modelers to help them make a better design in just two days of CATIA Hackathon. Next, we will expand the story behind each design process in detail.
I. Concepts & Sketches
Exchanging preliminary ideas.
Sketches
II. Model construction based on Mechanical Design, Human Design and Imagine & Shape
Imagine & Shape (hereinafter referred to as IMA) module is famous for its flexibility, rapidity, and high quality. In the design process of SEC-X, IMA is not only a modeling tool but also helps the promotion of the concept with its real-time G2-continuity modeling ability.
Interior surfaces by IMA
As we all know, in addition to the modeling ability, the mechanical, assembly and other functions of CATIA are also killer apps. In fact, mechanical-related functions are not only the patent of engineers but are also sharp weapons of designers.
The following two figures show the two modes of SEC-X. Through Mechanical Sys. Design, Assembly Design, and other modules, with the help of CATIA structure tree, can rotate the upper cabin together with everything inside simultaneously, without any additional operation. At the same time, the upper and lower limits of rotation degree can also be designated to switch accurately between the two modes, helping ensure the compatibility of multiple modes.
The rear of the car is raised in the exploring mode.
The rear lowers down in driving mode
The same method is also applied to explore the way of skylight's opening and closing.
In the design of vehicles, ergonomics is also an important factor. With the help of Human Design, we can also store the different actions and postures of passengers/drivers. Focusing on human behavior, designers can ensure that the design of the vehicle can meet the various needs of the driver/passenger. Cooperating with the Mechanical Sys. Design and Assembly Design, we are also able to design how the parts in the car match the actions of the person. Following pictures shows how the seat fit the driver's actions:
Exploring Mode
Driving Mode
Switch between different positions
Adjust the angle of the seat
III. Parametric texture development with xGenerative Design
The renderings at the overture should have illustrated the expressiveness of parametric patterns. Given that the use of XGD and its cooperation with apps like ICEM have been discussed in detail in previous Hackathon articles, we will not go in-depth here.
IV. Detailed explanation of materials in CATIA
Having finished modeling, we are to shade the model. Shading & material plays a vital role in visual communication & validation: the manifestation of texture, details, and emotions would be impossible without good shading & materials. So, we're going to explore how to make & apply materials in CATIA Live Rendering.
By opening the create material panel, a bunch of options pop up. In fact, materials such as Clear Glass, Basic, Car Paint, etc., can be regarded as simplified instances of Complex material, which based on the idea of physical rendering (PBR, Physically Based Rendering).
Complex material, as the name implies, is very complex. So it has the powerful ability to describe most materials. The significance of providing simplified materials is that for specific types of materials (such as plastic, glass, metal), specific parameters are often fixed as there's no need for modification. These contextually unnecessary parameters are thus given their default values and hidden, only limited parameters are exposed to users. Therefore, once we understand the principles of parameters in Complex material, we will master the overall logic behind other CATIA materials. Therefore, later on, we will dive into the essential parameters of Complex Material.
If we want to make a richer and more realistic material, we can also import Substance materials in CATIA. In the example of this article (i.e. shading SEC-X), most materials are Substance materials. On the basis of understanding Complex material, we will also see how to use and adjust Substance material in CATIA to acquire visual attraction and plausibility of a higher level.
So first of all, let's briefly go through the basic principles of the material (some advanced parameters are skipped).
Diffuse
First of all, let's take a look at the well-known Diffuse parameter:
We all learned the concept of diffuse reflection in high school. In PBR rendering, however, things are more than that simple. In fact, objects with smooth surfaces may also have Diffuse, while objects with rough surfaces do not necessarily have Diffuse (such as rough metal, as discussed later). In fact, the phenomenon of diffuse is formed by the irregular rebound of light through the interior of the object, as shown in the figure:
Image from "Real-Time Rendering, 3rd Edition", A K Peters 2008
This picture shows how lights interact with non-metallic surfaces. We can see from the figure that the light reflected directly by the surface is called Specular. We note that in addition to Specular light which directly reflected by the surface, the other part of the light refracted enters the object, absorbed by the particles narrowly beneath the surface, and the rest are scattered out of the surface in all directions.
Image from "Real-Time Rendering, 3rd Edition", A K Peters 2008
As shown in the figure, candles are typical of this kind of scattering. However, experienced readers must have noticed that this is not what we often call the Diffuse, but the so-called subsurface scattering (later called SSS)!
In fact, there is no essential difference between Diffuse and SSS in principle, as shown in the figure:
Image from "Real-Time Rendering, 3rd Edition", A K Peters 2008
The green circle in the figure represents the size of a pixel. When the situation is like shown in the upper left, the exit point of all scattered rays are within one pixel, and we can simplify the situation to the upper right picture, that is, the position of the scattered lights exiting the surface is equivalent to the position where the incident light touches the surface (i.e. exit point = incident point). At this point, the scattered light is Diffuse. Generally speaking, plastic, wood, paint, rubber and other materials are satisfied with this situation.
When the situation is shown in the figure below, a lot of scattered rays exceed the range of one pixel, and the scattered light is called SSS. This is the case of candles, soap, jade, human skin, and other materials.
Careful readers must have found that the previous schematic diagrams are all about "non-metallic materials." So, how does metal surfaces interact with lights? In fact, the situation is very similar, or even more simplified, as shown in the figure:
Image from "Real-Time Rendering, 3rd Edition", A K Peters 2008
For (pure) metal surfaces, the light refracted into the surface is immediately absorbed by free electrons in the object, so there is (almost) no Diffuse and SSS, observers can only metal surfaces by accepting Specular.
Below, we will apply the above theory to the three parameters related to Diffuse in the Complex material:
- Diffuse Color refers to the inherent color of an object. In general, it is the color scattered by the object without any absorption or transparent/translucent and is directly irradiated by a pure white light source. According to what has just been discussed, the Diffuse Color of pure metal should be black or very dark color. Alloy, rust and other materials are not pure metal, so a certain amount of Diffuse Color will work.
As you can see, if a high Diffuse is applied to the conductor, the result will be implausible.
- The value of Diffuse Weight is between 0 and 1. Generally speaking, it describes how much refracted lights exit the surface (as Diffuse), rather than be absorbed. When the value is less than 1 (p. S., if no texture map, the value is usually less than 1), indicating that part of the energy is absorbed after the light is refracted into the object.
- Diffuse Glossiness describes the directional tendency of Diffuse rays. The higher the Glossiness, the flatter, and darker the object will appear. For more accurate explanation, simply search Oren-Nayar for further understanding.
Diffuse Glossiness increases gradually from left to right
Specular
We've discussed the difference between Specular and Diffuse/SSS earlier, and we've generally explained the principle of Specular.
Image from "Real-Time Rendering, 3rd Edition", A K Peters 2008
But this picture seems to conflict with what we have learned in high school: the surface in the picture looks like a smooth surface. For a smooth surface, its specular should look like this:
That is to say, the reflected light should not be forked. So, is our earlier explanation wrong? Why reflected lights (specular rays) fork even when the surface looks smooth?
In fact, the principle is similar to what we used to distinguish Diffuse from SSS. Take a look at the figure below:
Macroscopically, the surface of the ball is smooth, while on the microscopic scale, the concavity and convexity of the surface will cause parallel light to be reflected in different directions. However, because the concavity and convexity are extremely microscopic and far less than one pixel, we also combine these incident rays and assume that all reflected lights are emitted from the same point, and we have our previous diagrams. The degree of bifurcation determined by the roughness/glossiness of the surface (Specular Glossiness): the rougher the surface, the more divergent the reflected light, and vice versa, as shown in the following figure:
Just like what we did when exploring Diffuse, we can divide the materials into two categories: metal and non-metal:
As you can see, for typical non-metallic materials, the Specular Color should be white (in complex CMF, this limit can be broken. But common household appliances, building materials, etc. follow this rule); for metal materials, Specular Color can have a color tendency (although it is often of extremely low saturation. Materials like gold or copper are rare).
However, just set up the Diffuse Color (as mentioned before, the metal Diffuse Color must be very dark，even black) and reflect the color is not enough to reach the effect shown above.
In order to convert a material between metal and non-metal, in addition to the parameters of Diffuse Color, Diffuse Weight, Specular Color and Specular Weight mentioned earlier, there is a vital parameter to adjust — Index of Refraction (later called IOR). The IOR of non-metals should often be set relatively lower (about 1.33 to 2.0, a few materials, such as gems, have an IOR of 2.0 +), while metal materials tend to be very high (practically higher than 10, although in real-world the IOR of metal is a complex number).
Next, let's take a look at the difference between not adjusting IOR and adjusting IOR when converting a metal material to a non-metallic material:
Similarly, let's take a look at the difference between not adjusting IOR and adjusting IOR when a non-metallic material is adjusted to a metal material:
Seeing these, we can't help but ask, why is this IOR so adept, and what kind of change has it brought about by adjusting IOR? Let's start with an experiment: we turn off the diffuse, set the specular color to yellow (gold), and then adjust the IOR to 1.45 (the IOR value of the general plastic), 2, 5, and 25 (metal), respectively, as shown in the figure:
Here, taking the rendered map of IOR=25 as the base map (notice the layer panel), we extract the spheres of different IOR separately and place them on them (in this case, IOR=1.45 as an example), and then change the blending mode to "subtract". As the name implies, this hybrid pattern is used to calculate the difference value of each pixel between the upper and lower layers. The methods are as follows:
Since the image is not stored as a linear floating point value, but a 8bpc image with Gamma correction, the following results represent only trends, not physically accurate results
In this way, we get the differences of each pixel between the balls of different IORs and the metal ball of IOR=25, to clarify the affect of IOR. The results of the operation are shown as follows: the left column is the original renderings of the balls, and the right column is the value of the differences between the left column and the ball of IOR=25. Note the differences at gaze angle (shown in the red circle) and near the center (shown in the green circle):
Let's take a look at this diagram:
The last row of spheres is pure black, which is quite natural as it shows the difference between the sphere of IOR=25 and the base map (whose IOR is also 25).
As the IOR rises, we can see that the differences are decreasing (that is, the spheres in the right column get darker and darker as the IOR on the left increases). Behind the overall darker trend, however, we find that the changing part is mainly near the center (shown in the green circle), while the marginal part (shown in the red circle) is always pure black. This means that no matter how the IOR is adjusted, no matter whether our material is metal or not, the specular on the edge of the material is no different from that of IOR=25. And we can clearly see that when IOR=25, regardless of the edge and center, the specular is extremely strong. As a result, we can conclude that no matter how the IOR is adjusted, the specular at the edge maintains a very high intensity, and only the specular intensity of the central part is changed. This phenomenon is called the Fresnel effect (Fresnel Effect).
- Note: the "edge" here actually refers to the part where the tangent direction of the surface is almost parallel to the line of sight (i.e. the normal direction is almost perpendicular to the sight direction). The specular intensity of the "central" part (that is, where the normal direction is parallel to the sight direction) is called F0. Changing IOR is actually changing F0.
For non-metallic materials, F0 is about 2% to 5%, and a few (such as gems) can reach 8%. For metal materials, F0 is between 70% and 100%.
Let's take a look at a set of renderings and feel the Fresnel effect intuitively:
You can see that from top to bottom, as the sight direction is more and more perpendicular to the blue plane, the reflection of the yellow ball and the environment on the blue plane are getting weaker and weaker.
Through the above analysis, we have basically learned how to set the material of homogeneous (that is, no texture) transparent objects. Before the summary, we still have another small experiment.
In the above description, are there any doubts about the division of labor between Specular/Diffuse Color and Weight? Let's take a look at what kind of role they play. For Specular Color and Specular Weight:
As you can see, as long as the product of Specular Color and Specular Weight remains the same, the final effect will not change. if you want to verify accurately, you can try to set the blend mode to difference in Photoshop as we experimented with IOR before to see if the result is pure black. Similarly, for Diffuse Color and Diffuse Weight, as long as the product of the two remains the same, the final effect becomes the same. Take a look at the figure below:
Separating the two (i.e. Color & Weight) have its own advantages and disadvantages. Advantages include:
- The intensity of Specular and Diffuse can be adjusted quickly by Weight parameters, or be turned off without changing the color tendency of Specular and Diffuse.
- Because objects in the physical world absorb the incident light (energy loss) more or less, there are few pure white Specular and Diffuse (that is, both Color and Weight are 1). Therefore, keeping the Weight parameter at 0.9 (or below) can relatively ensure the plausibility.
- Even if a texture is applied to Color channels, the strength of Specular and Diffuse can still be tweaked by the Weight parameter.
There are also shortcomings:
- In some cases, more parameters to adjust is not that convenient;
- The increase in the data required to describe the material slows down the rendering speed to some extent (especially when the material and the scene is complex, and when real-time preview).
- Based on this, many scenes that require high rendering speed (such as games) generally choose to merge Weight and Color, that is, from Specular Weight, Specular Color, Diffuse Weight, Diffuse Color to Specular and Diffuse, where:
- Specular = Specular Weight * Specular Color
- Diffuse = Diffuse Weight * Diffuse Color
- The PBR maps you download from the network are basically Specular and Diffuse, no longer subdivided into Color and Weight parameters.
After understanding the above facts, you can adjust these two sets of parameters according to their own needs.
Summary
For regular opaque objects, you can follow these steps to create:
1. Adjust Specular Weight and Diffuse Weight to 0.9 (or adjust to values such as 0.8 according to your preferences or needs)
2. Determine whether the material is metallic or non-metallic
- If it is made of metal, then:
- Turn Diffuse to very low or close directly
- Set IOR to more than 10
- Tweak Specular Color (optional)
- If it is a non-metallic material, then:
- Set IOR to 1.33-2
- Set Specular Color to white
- Configure Diffuse Color
3. Adjust Specular Glossiness and Diffuse Glossiness according to visual effects, maps, or physical data
4. Further adjust Specular Weight and Diffuse Weight according to your needs
Refraction / Transparency
Limited by space constraints, the parameters related to Transparency are not explained in depth here. You can hover over the name of the option, and there will be tips with images & texts:
Welcome to explore by yourselves with the help of the tips and the previous comparative experimental methods.
However, it is important to point out two small points that are not mentioned in the tips and may not be easy for you to discover on your own.
First of all, in order to get the physically correct result, Specular Glossiness and Transparency Glossiness should be consistent. Let's take a look at the comparison:
As we can see, plausible results can be achieved only when Glossiness is consistent.
Similarly, if you want to get physically correct results, the IOR in Reflectance should be consistent with the IOR in Volume (reflecting IOR and refracting IOR), as shown in the figure:
The reason why these two sets of parameters need to be consistent is that both reflected and refracted light occur on the surface (see figure below), while the Glossiness (smoothness) and IOR (ability to deflect light) on the same surface are the same.
Remember this picture?
In addition, among the common non-metallic materials, only gems' IOR > 2. At this point, we can try to add some dispersion through the Abbe Number:
Reading here, I believe you already have understood the logic behind most materials.
Practice: Shading SEC-X
We've already finished model of SEC-X. Now, let's shade it.
Glass Shield Material
First, let's create a new Clear Glass material for the top cover so that we can see through it. Simple & easy.
Lights Material
Lamp material is not difficult either. Create a new emissive material and then assign to lights shown above.
Titanium Substance Material
First, create a Substance material through the Create Appearance Data from Substance command. The interface is shown in the figure. Here we can select a brushed titanium material from the disk. Sometimes the Convert to Specular/Glossiness button appears in the Select a Substance Graph to Import tab, simply click it.
One of the benefits of Substance material is that while we have detailed materials, we still maintain a considerable degree of freedom of modification (compared to using maps). Here, we first set the Output Size to the highest level to make sure there are enough details.
Take the Roughness material as an example. First we can try setting Roughness to its minimum. As you can see, we get a specular smooth material.
Similarly, we can set the Roughness to white (maximum), and the result looks very rough.
Of course, for the final effect, let's set the Glossiness to medium value and get the effect shown in the figure above.
Car Paint Material
We are going to create a car paint material for the chassis and the bottom part of the cabin. Since we focused on the Complex material earlier, we simply create our car paint directly through Complex.
The basic parameters, such as Diffuse, Specular, have been discussed in detail before, thus we are not going to repeat them here. Compared with the ordinary material, the car paint material mainly has the following options:
- Edge Color: many car paint edges will become darker, but because we are making black paint, for the time they can be pulled black;
- Flake: sparkling sequins, necessary for pearlescent paint;
- Coat: the varnish of the surface, improving the sense of quality to some extent, as shown in the figure below (note the brightening near the edge and the concurrence of both sharp and fuzzy reflections)
Carbon Fiber Substance Material
Once again, we use the Create Appearance Data from Substance command to import Substance materials. This time we continue to explore the possibility of Substance materials by creating a carbon fiber material for the interior.
First of all, we can adjust Output Size and Tile to achieve the accuracy of the details we need, in order to create texture.
We can then try to adjust the Metallic from 0 to 1. As the name implies, Metallic describes how metallic or non-metallic a material is. 0 means non-metals, whereas 1 means metal.
However, any value other than 0 and 1 is not recommended. The reason is complex, a "TL;DR" version is, that values other than 0 and 1 can hardly correspond to any material in the physical world, making it difficult to guarantee authenticity and consistency in different lighting environments.
Other Materials
We also use Substance material to create Alcantara, weave and other materials. But CATIA can do much more with Substance materials.
Ocean Material
Yes, we can also use Substance materials to quickly build the environment to convey feelings, by creating materials such as wooden floors, cement, grassland, tundra, and even the sea.
As usual, create a Substance material. In order to ensure enough detail, we set the Output Size to a maximum of 2048. Because the material here is not very standard, there is no Tile option to use. Here we can consider raising the Scale in the Material Application Mapping tab (see figure below):
In order to make the ocean surface more stereoscopic real, we can turn on Displacement and Bump in Height Map and Normal Map, respectively.
Lighting and Camera Settings
Next, we can adjust the camera to the perspective we appreciate, and then store the current view through the Create Camera command. We can also manage and modify the various parameters of the camera through the Manage Camera command.
Once the camera has been determined, we can also use the Manage Ambience command to apply our favorite HDRI maps and configure lights through Manage Lights.
Finally, we can also turn on Bloom, DoF (Depth of Field), Tone Mapping and other special effects, and then finally render.
Creative Design xGenerative Design Natural Sketch
