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PRODUCT LIFECYCLE MANAGEMENT COMPETENCY CENTRE

RENDERING

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Table of contents

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1.0 OBJECTIVES Nowadays, images are everywhere: advertisings, movies... If you have good pictures, you’re able to make easier communication and also it help you to pay attention of customers. The objective of this course is to help you to make better images. This course involves: • • • • • •

Some remind about physics. Some knowledge about raytracing and associate vocabulary. Materials Lighting Photo Studio workshop. Real time rendering.

1.1 PHYSICS A very simplest way to explain what is the light is to tell that the light is made up of balls called photon. Quantity of energy of a ball depends on wavelength λ. If a ball is big, it means it had a lot of energy so the wavelength is small (from blue side spectrum). On the contrary, small balls have less energy and the wavelength is high (from the red side spectrum). From a monochromatic light, all balls have same size, but light from a bulb have balls from several sizes.

The colour of an object is not actually within the object itself, it depends on how object interact with light. So, it depends basically on material characteristics of the object. If a material of an object absorbs all colour except blue, so the blue will be reflected to your eye and the object will appear blue.

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For transparent object, some colors will be transmitted through the object and others will be reflected.

Ray light

Red reflected ray to your eyes

Transmitted ray

Red glass

1.1.1 SPECULAR REFLEXION Reflexion is called specular when all incident rays are reflected, but in reality some rays are absorbed or diffused by the material. Quality of the reflexion depends on quality of planarity of the surface. If defaults are less the size of the wavelength then the surface reflected all rays.

1.1.2 DIFFUSE REFLEXION But when the surface of an object had a lot of defaults then reflected rays are going in several directions (so it’s diffuse)

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Some representative refractive indices

1.1.3 REFRACTION A ray which goes through a transparent object is deviated regarding refractive index of the material of the object.

Material

n

Vacuum

1 (exactly)

Helium

1.000036

Air

1.0002926

Carbon dioxide

1.00045

Water Ice

1.31

Liquid Water (20째C)

1.333

Cryolite

1.338

Acetone

1.36

Ethanol

1.36

Teflon Glycerol Acrylic glass Rock salt Crown glass (pure) Salt (NaCl) Polycarbonate Flint glass (pure) Crown glass (impure) Bromine Flint glass (impure) Cubic zirconia Diamond Moissanite Cinnabar (Mercury sulfide) Gallium(III) phosphide

1.35 - 1.38 1.4729 1.490 - 1.492 1.516 1.50 - 1.54 1.544 1.584 - 1.586 1.60 - 1.62 1.485 - 1.755 1.661 1.523 - 1.925 2.15 - 2.18 2.419 2.65 - 2.69 3.02 3.5

Gallium(III) arsenide

3.927

Silicon

4.01

1.2 RENDERING ON CATIA V5 Because of the multitude of the rays coming from different light source, to calculate a photorealistic image according to each material and lights composing the scene, will be very long to calculate in reality. So to reduce considerably the time to calculate this image most of rendering software are making ray tracing. Instead of going from the light to the camera, the computer calculates from camera to light source. A virtual image is created in front of the user (final image) and from each pixel composing this image, the software launch a ray to the light source. So, the pixel colour will depend on object material touch by the ray. Like this, the computer calculate only rays view by the eye of the user, it reduce a lot the rendering time.

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Light

Camera

Catia is using third party software integrated in Photo Studio workshop call Mental Ray v3.3. Photo Studio is able also to do Final gathering, global illumination, caustics, depth of field, halo, and cartoon. We will see later in what can improve these features.

2.0 MATERIALS When you apply a material to a part, it gives to Catia information for Analysis but also for Rendering. You can find a lot of ready to use material in Catia but you can also customize them to make them much more realistic when rendering. We use a part that can show you effects simultaneously on a cylinder, a box and a sphere. We apply a Plastic material under 2 white light and we customize it to see effects of each options.

Let see, which the different lighting option of a material have.

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2.1 AMBIENT

Ambient give the abilities to a material to be self Illuminating. There is less shadows on it. By clicking on 3 dots buttons you can select the material colour.

Ambient = 0.10

Ambient = 0.60

Ambient = 0.95

2.2 DIFFUSE By clicking on the chain we can unlinck the color between Diffuse and Ambient. But there is few material with a different color for Ambient and diffuse.

Ambient (Blue) = 0.95 / Diffuse (Red) = 0.95 So let it link with ambient color, we let it blue. PLMCC, JSS Academy of Technical Education, Noida

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Diffuse colour will be the one send back to your eyes.

Diffuse = 0.10

Diffuse = 0.50

Diffuse = 0.95

2.3 SPECULAR Specular on a material is the light reflects. You can also choose another colour than generally white to give effect of a different light colour.

Ambient = 0.3 / Diffuse = 0.8 / Specular (Red) = 0.6 Let see on the table under impact of a value with a white specular.

Specular = 0.10

Specular = 0.50

Specular = 0.95

For example, for a matt material put specular value at 0.

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2.4 ROUGHNESS Lower this value is, smoother the material is, so shininess is less diffuse.

Roughness = 0.10

Roughness = 0.50

Roughness = 0.90

Don’t use values more than 0.90, it give strange results.

2.5 TRANSPARENCY / REFRACTION Transparency and refraction are coming together, because if you’re using refraction without any transparency, you’ll get nothing more in your picture. Below refraction = 1

Transparency = 0.20

Transparency = 0.60

Transparency = 0.80

Refraction = 1.20

Refraction = 1.50

Below transparency = 0.6

Refraction = 1

You can refer to 1.1.3 to have some ideas of refraction value. PLMCC, JSS Academy of Technical Education, Noida

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2.6 REFLECTIVITY

Reflectivity = 0.10

Reflectivity = 0.50

Reflectivity = 0.90

At 0.9 material is so reflective that it looks like a mirror...

2.7 TEXTURING Don’t waste too much time to go through texturing to get marble or rock aspect because you can get good one from default materials. You can use texturing as well for materials like marble, but you can use it as a way to add bump on your material. Possibilities are very interesting to add scratch etc... See example below.

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Complexity 1 to 8

Perturbation 1 to 8 (Complexity 8)

Gain 0.1 to 1.3

Amplitude 0.1 to 0.9 (bump 1)

Bump -10 to 10 (amplitude 0.1)

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You can also use image as a texture on your part, like below. Use Image in type, and use the appropriate mapping type (planar, cylindrical, sphere...) and size.

Images use

Results

Parameters (same for both)

You can move and scale the image on your object by the position and scale U & V, bump can give a little roughness also.

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3.0 REALTIME RENDERING Now you have a good knowledge and idea of materials parameter, now let see Realtime rendering workshop. It’s nothing more than a workshop where you can add a camera view, lights and an environment to create your scene. There is no output rendering here, rendering will be made in real time on the main window. The only thing to do is to active, in custom view mode, shading material...

What you get by default

What you get in realtime rendering (if you apply material)

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But there is some limitation in realtime rendering : - No refraction visible - Reflectivity is fake (just a texture apply) - If reflectivity is more than 0.2 you will not see the texture you have apply (can’t show textures and reflectivity in same time) But since R16, CgFx from Nvidia is implemented in CATIA and it improve Realtime rendering if your graphic card is strong enough (see paragraph 3.4 for more information)

3.1 CAMERA Under construction

3.2 LIGHTS Under construction

3.3 ENVIRONMENT I don’t advice you to use it, because, material possibilities are less on environment than using a plane part in an assembly with a material applies on it.

3.4 CgFx As we told in paragraph 3.0 you cannot see texture if reflectivity is more than 0.2. But, if you activate in Tools/Options/Display/Performance/Miscellaneous: Enable OpenGL Shader

You will be able to get both texture and reflectivity in real time rendering.

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Once OpenGL Shader enabled you can also use CgFx shader, to get more realistic real time rendering. Edit your material and select in texture “External Shader�, then you can select a .fx shader. You can find shaders in : C:\ProgramFiles\DassaultSystemes\B17\intel_a\startup\materials\shaders\

You can select for example in Painting\CarPaint\ the CarPaint.fx file

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Now with CgFx shaders, you can render bump, reflectivity, textures in same time in real time rendering.

4.0 PHOTO STUDIO Under construction

5.0 CASE STUDY Under construction

5.1 5.2 5.3 5.4 5.5 5.6

METHODOLOGY SET THE SCENE APPLY MATERIALS SET CAMERAS SET LIGHTS FINAL RENDER

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