Read mentalray.for.aec.renderings.pdf text version

mental ray in 3ds Max Design for AEC renderings

1

The Basics

Materials

Recommended Material Types

The flexibility of mental ray and the evolution of 3ds Max and 3ds Max Design created some confusion around which material should be used with mental ray. Here is my advice: for 99% of the AEC rendering workflows, you will want to use the A&D material or the ProMaterials (ProMaterials are simplified interfaces driving the A&D material under the hood). The other materials will work, but the A&D material contains mental ray specific optimizations that will guarantee speed and quality over, for example, the traditional Standard material or the legacy Architectural material.

The A&D Material functionality is described in details here: http://www.mentalimages.com/fileadmin/user_upload/PDF/arch_and_design.pdf

Subtle reflections on Wall Paint automatically created by the ProMaterials

The highlights materials are the recommended materials to use for your AEC renderings.. Right: ProMaterial WallPaint, Wood, Concrete and Ceramic at works. (Models: Maximilian Tarpini)

mental ray in 3ds Max Design for AEC renderings

2

Lights and Shadows

Units and Scale

Physically based lighting computation implies that light attenuates using the inverse square falloff law, which simply means the intensity of light declines exponentially with the distance it travels. Therefore, it is crucial that the scale of your scene corresponds to realworld data--otherwise the results will get corrupted. A common mistake for example, is to import an airport at the size of a shoebox or a room at the size of a stadium. In one case, the lighting computation will be too bright, and in the other case, it will be too dark. To verify your scale settings, check the "System Unit Scale" settings in the "Customize | Units Setup | System Unit Setup dialog box":

System Units Setup of 3ds Max Design

Recommended Light Types

The recommended light type are the Photometric lights and the mrSun and mrSky . They simulate realworld values and play nice with indirect illumination computations and camera exposure.

mental ray in 3ds Max Design for AEC renderings

Recommended Shadow Settings

The recommended shadow type for typical architectural rendering in 3ds Max Design is the Ray Traced Shadow type. While this might not have been true in the past, ray traced shadows are faster to compute than shadow maps, less memory intensive and handle transparency better. This is used by default in 3ds Max Design 2010 but not in 3ds Max 2010.

3

Exposure Control

Recommended Exposure Control Settings:

The recommended Exposure Control plugin to use is the "mr Photographic Exposure Control". It is designed to mimic real world camera settings and assumes that the scene environment is physically based as well (Sun, Sky, Photometric lights, proper scale etc.).

The mr Photographic Exposure Control is recommended.

Conclusions / Recap on the Basics:

1. 2. 3. Use an A&D Material or ProMaterials on all objects. Use mrSun and mrSky , Photometric Lights and Raytraced Shadows. Use the mr Photographic Exposure Control.

mental ray in 3ds Max Design for AEC renderings

4

Simplified mental ray render panel

Scene: 00_global.knobs.basics.max

The simplified mental ray render panel is meant to reduce the learning curve for Revit users and accelerate test renders by providing you fine tuning knobs for Shadows, Reflections and Refractions:

Launch the Exposure Control Panel

Glossy Reflection

Edge Antialiasing

Glossy Refraction

Soft Shadow

Enable/Disable Indirect Illumination Cache Indirect Illumination to Disk

mental ray in 3ds Max Design for AEC renderings

5

Exterior Daytime Rendering

Scene: 01_exterior_rendering.max

Daylight System

The Daylight System of 3ds Max Design regroups 2 light sources in the same user interface: the Sun and the Sky. Their intensity and colors are ruled by their orientation in the 3D space, which is affected by the Time and Position on Earth. The blue background is handled by a special shader that must be assigned in the Environment map: 1. 2. 3. Create a Daylight System; make sure it uses the mrSun and mrSky plugins and set the Time and Date. Enable the mrPhotographic Exposure Control and use the Exterior Daytime preset. Assign a mrPhysicalSky shader in the environment Map slot: this will add the nice blue background:

4. 5. Turn ON final gather: this will create the indirect illumination effect and become the Skylight. Render: you should get something like this already:

Background sky comes from the mr Physical Sky environment shader.

Direct illumination from the mr Sun light object

(All Models in this document based on an original file from: (c) 2007 Electric Gobo / Karcher, www.electricgobo.com)

Sky dome contribution comes from the mrSky light object + Final Gather

mental ray in 3ds Max Design for AEC renderings

6

Adding clouds in the sky

The mrPhysicalSky shader has the ability to change color and affect the appearance of the Sun Disk with the haze parameter. This parameter is mapable so it makes an excellent home for cloud maps: 1. 2. 3. Add a sky image in the Haze map of the mr Physical Sky. Don't forget to use the proper projection (Screen or Spherical for example) Increase the Output Value to ~8 to see the effect: this will drive the haze value of the Sky based on the image. Render: the clouds now appear on top of the cloud. They also change color based on the time of the day.

A cloud image (a simple photo) modulates the value of the Haze parameter of the procedural mr Physical Sky

A Haze map must provide values from a range to 0 to ~8 to be effective, hence the "boost" done with the Output Amount.

mental ray in 3ds Max Design for AEC renderings

7

Glare Shader (Bloom)

The Glare Shader is what we know as an "Output Shader". Output shaders are processed on top of the final image, as a post processing step. They can be assigned in the Render Setup dialog.

1. Add a Glare shader in the Camera Effects | Output slot of the Renderer Tab (Render Setup dialog) and instance it in the Material Editor:

2. 3. 4. The Spread parameter is the one that affects the most the image. Render: you should see something like this:

Increase the contrast in the Exposure control to let the Glare shader finding the hotspots.

Glare shader effect. The streak comes from the Streak image.

The Glare Shader adds the small "spark" to the image.

mental ray in 3ds Max Design for AEC renderings

8

Exterior DayTime Rendering Tips and Tricks

1. 2. 3. 4. The illumination on the surfaces is provided by the Sun and Final Gather and not the Environment Map! You do not need many Final Gather Bounces to have a meaningful effect: Final Gather bounces are usually useful for interiors. The ground has an effect on indirect illumination: if you use a very bright green grass, your building will probably turn greenish as well. To get the Glare shader working, you need a high contrast image: the Glare shader analyzes the rendered image and adds the "sparkles" to it. If the image is too faint, boost its contrast with the Burn parameter of the Exposure control. Use the Exposure Preview to quickly preview the image's brightness.

5.

mental ray in 3ds Max Design for AEC renderings

9

Interior Daytime Rendering

Scene: 02_interior_rendering.max

Sky Portals + Final Gather & Multiple Diffuse Bounces

The strategy do adopt with interior renderings is to identify windows and openings with a special light object that is called a "Sky Portal". Its job is to focus rays from the environment through the windows and holes and avoid wasting a lot of rendering time with traditional Final Gather computation.

The mrSkyPortal functionality is described in details here: http://www.mentalimages.com/fileadmin/user_upload/PDF/arch_and_design.pdf

mr SkyPortal Light object positioned in front of a window, pointing inside the room

1. 2. 3. 4. 5.

Once you are satisfied with an Exterior rendering, add a Sky portal in front of the windows of the building. Make sure their arrow point inside the space as illustrated: this indicates the direction of the light flux. Move your camera inside. Change the Exposure control to an Interior Rendering preset: this will adjust the aperture of the camera to interior lighting conditions, which are darker than exterior spaces. Increase the Final Gather diffuse bounces to ~34: this will bounce the light around inside the space.

mental ray in 3ds Max Design for AEC renderings

6. Render: you should see something like this:

10

Exterior is washed out because our exposure control is adjusted for interiors.

Soft and subtle direct shadows from the sky dome come from the mr SkyPortal light

Lighting is only from indirect illumination bounces.

FG bounces determines the number of time light will bounce inside your space. A value from 3 to 5 is typically recommended for interior spaces.

mental ray in 3ds Max Design for AEC renderings

11

Interior DayTime Rendering Tips and Tricks

1. Use the Material Override from the Render Setup | Processing tab to understand the lighting distribution of your space. This will allow you to see the lighting effects on a neutral color as opposed to be distracted by reflections, refractions and textures Note, however, that you need to temporarily hide the glass panes in your windows, as this material override will turn them opaque as well, which will prevent the light from outside coming inside:

An interior rendering with the materials overridden by a neutral diffuse white material

2. 3.

Cache the Final Gather computation to disk: once it is baked to disk, you can rerender without recalculating indirect lighting (which can be time consuming) during material tweaks. Use very low quality settings to tune your materials: the rendered image will be completed faster.

Global tuning knobs allows for faster control on all the scene materials and lights for faster tuning.

4.

The Shadow Samples affects the quality (graininess) of the shadows from the Sky Portals. It is also controlled by the Global "Soft Shadows Precisions" slider in the Rendering panel:

mental ray in 3ds Max Design for AEC renderings

12

Ambient Occlusion

Scene: 03_ambient.occlusion.max

Ambient occlusion has the benefit of enhancing the small details and creates what we commonly call "contact shadows". Ambient occlusion is enabled directly in the A&D and ProMaterials. Typically you will want to enable it for floors, door frames and other areas with fine geometric details.

Typically, light leakage arises due to low density of FG calculation .Objects appear to be floating. Ambient Occlusion will help solving this issue.

Without Ambient Occlusion

With Ambient Occlusion, edges are visually enhanced.

The larger the distance is, the more pronounced the effect will be. Usually, you want to use a distance of ~10 cm.

With Ambient Occlusion

mental ray in 3ds Max Design for AEC renderings

13

Interior Nighttime Rendering

Scene: 04_interior.rendering.photometric.lights.max

Photometric lights

We recommend using Photometric lights for interior renderings because their energy computation is physically based, which makes them ideal sources for indirect illumination calculations. The main reason for this is that the energy used in the indirect illumination process will always be in balance with the energy used for the direct illumination. 1. Start with an Exposure Control preset set as follow. You will readjust later but it's a good starting point: 2. Create Photometric Lights in the space. As a reference here are typical intensities corresponding to real world lighting values:

Class Narrow Narrow Medium Wide Wide Wattage 20 W 20 W 50 W 20 W 50 W Type Spotlight Spotlight Spotlight Spotlight Spotlight Intensity 3300cd 9150cd 3000cd 460cd 1500cd Beam Angle 6 12 25 38 38 Field Angle 12 25 50 75 75

3.

Turn OFF Final Gather and Render: you should get something like this where only the direct illumination is calculated:

Direct lighting only

mental ray in 3ds Max Design for AEC renderings

4. Enable Final Gather, with 34 Diffuse bounces:

14

Indirect lighting was bounced from the contribution of the direct lights. The "splotches" are caused by low quality final gather settings. See the "Fine Tuning Indirect lighting" section for more tips on how to solve this.

With a better FG solution splotches disappear. See the "Fine Tuning Indirect lighting" section for more tips on how to achieve this.

mental ray in 3ds Max Design for AEC renderings

15

Glow and self illumination

Scene: 05_interior.rendering.photometric.lights_self.luminous.max

The A&D material exposes a Self Illumination feature that allows turning materials into a light source. The light transport is done via Final Gather so the quality of its shadows directly depends on the Final Gather accuracy. 1. Enable Self Illumination in a given A&D Material. You can decide if this contributes to Reflections and/or Illumination at the Material level. If you use a texture Map, the texture will modulate the color of the emissivity: A map can be used to simulate video walls of LED

walls

The intensity rules how bright it is. Keep in mind that with Exposure Control enabled, you may find yourself having to go to relatively high values.

2. 3. Turn Off all the lights to see its effect isolated. Render: You should get something like this:

This is where you decide to contribute to the scene lighting or to reflections.

Final gather "sees" the luminous surfaces.

Self illuminated material with contribution to Final Gather rays. No lights used in the scene.

mental ray in 3ds Max Design for AEC renderings

16

Photometric lights turned back on with a color filter.

mental ray in 3ds Max Design for AEC renderings

17

Fine Tuning Indirect lighting

Basic strategy

To fine tune a Final Gather solution we recommend adopting the following strategy:

1. 2. Bake the Final Gather solution to disk using your normal lighting conditions so you can reuse it later and lock it in a Read Only mode. Use a Material Override with a Diffuse White Material: lighting is easier to visualize on a flat white surface. Since you locked the Final Gather solution, you don't have to bother about transparent objects anymore, except for the light coming from outside your building (i/e/ the Sun). Render with the Final Gather Diagnostics Mode (Render Setup Dialog | Processing Tab) to visualize the location of the Final Gather points contained in the FGM file:

3.

4.

Fine tune the interpolation settings: they can be changed even if your Final Gather solution has been locked.

mental ray in 3ds Max Design for AEC renderings

18

Examples

Test A: Low Density, Low Interpolation

"Cloudy" indirect lighting

Density relatively low

Observations:

We can see that the density of the Final Gather points is relatively low. The noticeable cloudiness is visible mainly where the Final Gather points are separated each other by a large distance (where the density is low). Since the Interpolation is also low, the result is the "cloudiness" effect.

mental ray in 3ds Max Design for AEC renderings

Test B: Increased Interpolation

By increasing the interpolation, we "blend" more points together, softening the solution.

19

Density still relatively low: no additional computation time.

Observations:

Here, we simply increased the Interpolation. We end up blending more Final Gather points together, a little bit like a "Blur" in an image. The Final Gather point's density is still relatively low which did not increase the computation time.

Tip:

When a Final Gather solution is locked and read from disk, you can change the interpolation between each rendering without having to recalculate the Final Gather solution.

mental ray in 3ds Max Design for AEC renderings

Test C: Increased Density

With a very large density of FG points, an Interpolation value of 150 is not enough here. A larger Interpolation value is required to smooth out the results.

20

An Interpolation value of ~450 is better: the more FG points you have, the larger the interpolation needs to be.

Observations:

If we where to increase the density of Final Gather points to capture more subtle light effects and details, the Interpolation required is now larger: as we have more points, we need to blend more points together to reach a smooth effect. Notice the "cloudiness" effect appearing again when we used an Interpolation value of 150. To fix it, we need to increase it up to 450!

Note:

The reason for the noise is usually caused by the stochastic nature (randomness) of Final Gather. To solve it you either have to cast more rays per FG points or increase the Interpolation. Note that the Interpolation parameter is essentially a "blur" which can remove or reduce the effect of subtle shadows.

mental ray in 3ds Max Design for AEC renderings

21

NonPhoto Real Renderings (NPR)

Ink & Paint Material

Scene: 06_NPR_InkPaint.max

The Ink & Paint material gives a toon look to objects. It can respond to lighting and shadows or give a completely flat appearance:

Ink & Paint material

Tips:

1. 2. 3. 4. The "Paint Levels" parameter of the Ink & Paint Material determines the numbers of gradients you will get on the material with lighting and shadows. For typical cartoon looks, disable Exposure Control, Final Gather and use "Standard Lights". Physically Based features generally don't play nicely with this type of material The quality of the Ink will improve with higher antialiasing. You can use a Falloff Map to drive the color of the Ink based on distance, direction etc.

mental ray in 3ds Max Design for AEC renderings

22

Ambient Occlusion & NPR

Scene: 07_NPR_AmbientOcclusion.max

Often, it is useful to quickly render a series of draft views of interior shots with no materials simply to explore camera views. To accomplish this one technique consists into using Ambient Occlusion as a way to illuminate a scene to get a feel for the overall depth of the space:

Single A&D Material with an Ambient Occlusion Shader in the Diffuse Color

Single Ink & Paint Material with an Ambient Occlusion Shader in the Paint Color

Tips:

1. An Ambient Occlusion shader does not always have to return black or white. The look above was achieved by returning a dark blue and pale blue color. The distance amount determines how much Ambient Occlusion will occur at the edges. Try to keep a value relatively low (i.e. ~10 centimetres) and increase as needed. Combine Falloff Maps and Ambient Occlusion to develop interesting looks:

2. 3.

One of the Ambient Occlusion's color is modulated by a Falloff Map

mental ray in 3ds Max Design for AEC renderings

23

Eliminating Indirect Illumination Flickering

Reference: 3dsmax.2010.mental.ray.animation.flickering.explanation.mov video Scene: 08.flickering.animation.reduction.max

Prior to 3ds Max Design 2010, animation flickering was caused by two main factors: · · When the Final Gather points are not "locked" on the geometry: they "slide" along the surfaces as the Camera move. Moving objects create Final Gather points that are "floating" or "ghosting" in the 3D space, introducing rendering glitches.

In 3ds Max Design 2010, indirect illumination animation flickering is eliminated by two main techniques: · To handle Camera movements, Final Gather points are shot from several locations along the Camera path. Final Gather become "locked" on the geometry, thus removing the "sliding" effect of those points across frames. This is what we refer as the "FG Projection Mode". To handle moving objects, one Final Gather file per frame is processed in a first pass. When the beauty pass is rendered, Final Gather points are interpolated across multiple frames to "smooth out" the solution. This is what we refer as the "Frame interpolation for Final Gather Maps".

·

FG Projection Mode Tips:

1. 2. To be used if your Camera is animated. If your camera is static, it will not help at all. Works for typical "hero shots" where the Camera has a relatively slow movement (a pan, a dolly in). It will be less effective with long Camera Flythrough or fast camera movements.

mental ray in 3ds Max Design for AEC renderings

Frame interpolation for Final Gather maps Tips:

1. 2. Works only if you bake a unique Final Gather map to disk per frame as a first pass, which are then read as "read only" mode in a second pass. The first few frames and last few frames of your animation will not be able to interpolate to FG files that are missing (ex: frame 0 will expect frames 2 and 1 to be present). Therefore plan to pad your shots with a few extra frames in the beginning and in the end. The mental ray message window will display warnings about missing FG maps if any. As you load several FG maps in memory (one per frame to interpolate across), keep in mind that you also load a lot more FG points to interpolate across. You will need to increase the Interpolation value by a factor of maybe 3 or 5 to reduce the "cloudiness" that may appear. You can define a "bake FG Map" job on a network farm by using the following combination of "Passes" or "Jobs":

Pass 1: enable this to prevent the "beauty" pass from being rendered. You can then submit this as a Backburner job and get your network nodes baking to disk one FG file per frame. Pass 1: enable this to set FG to be in "write" mode. Pass 2: turn this off to get the beauty pass rendered.

24

3. 4.

5.

Pass 2: Use this option to turn FG in a "Read Only" mode.

mental ray in 3ds Max Design for AEC renderings

25

mr Proxies

Proxies are special objects that are designed to minimize the load on the viewport to maintain interactivity and accelerate the scene translation to mental ray. They are also optimized to reduce the overall memory footprint required to render large scenes containing many repetitive objects with millions of polygons. Proxies are "baked" to disk prior to be used by mental ray.

Scene capture: the trees and the grass are prebaked as proxies (image courtesy of Delta Tracing)

Final image (image courtesy of Delta Tracing)

Proxy Workflow:

1. 2. 3. 4. You need a geometric object already in the scene. Create an mrProxy primitive object. Assign it the object you want to bake to disk and bake it. Assign a material to the Proxy object (the material from the baked object will not carry through).

Proxy Tips:

1. 2. 3. Proxies are working on a single object basis at a time. If you grouped objects, you will still need a different proxy per object inside the Group. Use them on high poly count objects, typically entourage elements that you don't need to touch such as trees, cars, grass. For grass, create 23 variations of grass clusters, bake them to proxies and scatter them randomly as instances: from the visual point of view, you will perceive a large grass field. From the renderer point of view, it will still mean 23 objects... Use a MultiMap map to introduce slight random variation on repetitive objects. Many proxies instanced in the scene can have their own material for more variations Animated objects (deforming meshes) can be baked as a proxy too!

4. 5. 6.

mental ray in 3ds Max Design for AEC renderings

26

Linear Color Workflow (Gamma)

Reference: 3dsmax.2010.linear.workflow.mov video

While Gamma is not the topic of this paper, knowing that a material expects "linear colors" as input means that you need to handle Gamma properties which are usually embedded in image files. It is important that you "linearize" or "de gamma" textures as input.

Gamma Pipeline for Texture Input:

Typically, the Gamma pipeline for texture input works as follow:

Image File (*.jpg) (Gamma: 2.2) Image is Gamma corrected (DeGamma 2.2) Material (Material see pixels in Linear Sapce)

Bitmap Map

A Low Dynamic Range Image is loaded from disk, Gamma corrected (linearized) prior to be passed to the Material

Gamma Pipeline for Rendering Output:

Knowing that the Renderer operates in linear space (Gamma 1.0), the rendered image needs to be Gamma corrected (again) at the end prior to be saved on disk or displayed on screen:

Display Device (Gamma 2.2) Image is Gamma corrected (Gamma 2.2) Frame Buffer (Still in Linear Space) HDR Image saved to disk directly without corrections (Gamma 1.0) LDR Image saved to disk (Gamma 2.2)

Renderer (Operates in Linear Space)

An image is rendered in Linear Space. Depending on the target output, it is then Gamma corrected (Low Dynamic Range Images) or not (High Dynamic Range Images).

mental ray in 3ds Max Design for AEC renderings

Gamma workflow tips:

1. 2. If you save your textures out of Photoshop with a sRGB color profile, the closest matching Gamma value is 2.2: stick to this value. Low dynamic range images such as *.jpg files need to be Gamma corrected on input and output: when loading or saving them with 3ds Max, make sure that you load them with a Gamma correction of 2.2 as well:

27

Using the "System Default Gamma" option will take the value from the preferences dialog. The recommended default value is 2.2

3. High Dynamic Range Images should always be loaded and saved with a Gamma Value of 1.0. Since they are HDR, the convention is to assume is that they are always in Linear Space (Gamma 1.0).

mental ray in 3ds Max Design for AEC renderings

28

Additional documentation

The present document is far from being a complete mental ray reference. However, I have collected a few interesting links for you to look at..

Autodesk White Papers and Feature Videos

Revit to Max, Daylight Simulation and Analysis and more... http://www.autodesk.com/3dsmaxdesignwhitepapers Online feature videos: http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=10371032

Mental images documentation

A&D material, Sun and Sky and more... http://www.mentalimages.com/products/mentalray/documents.html

mental ray blogs

http://mentalraytips.blogspot.com/ http://mrmaterials.com/jeffsblog.html

mental ray in 3ds Max Design for AEC renderings

29

Appendix

Exposure Control

What is Exposure Control?

Physically based rendering requires exposure control, also called tone mapping. Tone mapping is the procedure of mapping a numeric lighting intensity in High Dynamic Range (HDR) from the scene into an RGB value of the pixels in the rendered frame. Physical light intensities range from zero to numbers approaching infinity in bright sunlight. The range of contrast available on display monitors is limited compared to this dynamic range, and common image formats are even more limited: JPEG images are eightbit images, ranging from a value of zero for black to 255 for white. In these files, white can only be 255 times brighter than black, a fraction of the range in the real world. Tone mapping helps compensate for the difference in range. Here are a few examples of reallife scenes measured with a luminance meter:

Sky luminance at horizon and zenith: 2600 cd / 360 cd / m2. Luminance on the leaves: 500 cd / m2.

Moonlit backyard, luminance on the roof of the garage: 0.22 cd / m2. Kids" play set luminance (brightest): 0.1 cd /m2.

mental ray in 3ds Max Design for AEC renderings

Assuming that the rendering engine can use realworld units for light sources (lumens, candela, or lux at distance) and realworld units for materials (reflectance), the resulting images will be beyond the range of what a monitor can display.

30

Therefore, it's necessary to compress the calculated image (ranging from zero to infinity) into a displayable image (ranging from zero to 255). This process is called tone mapping or exposure. To enable exposure control in 3ds Max Design, use the "Environment and Effects" dialog box:

Exposure Control Rollout in 3ds max Design

When you change the brightness and contrast controls, the light levels of your scene don't change; only the sensitivity of your camera does. This is far better than adjusting each light source in a scene one by one. If you want to shoot a photo, you would be more likely to adjust your camera's aperture or shutter speed than wait for the sun to set. The exposure controls control light in the same way.

The top image is exposed toward the inside of the room, and the bottom image is exposed toward the outer courtyard. Both are correct the light levels in the scene did not changed; the direction of the exposure is up to you. (c) 2007 Electric Gobo / Karcher, www.electricgobo.com

mental ray in 3ds Max Design for AEC renderings

31

Guidelines for your scene geometry

"Air tight" models

Sometimes, you can find models where walls and windows or roofs don't touch each other properly. This can cause lighting from the exterior of your building to penetrate without attenuation (from glazing for example) and introduce errors in the lighting analysis results.

Windows panes not touching the curtain wall frame, letting direct sun rays inside the model will falsify lighting analysis results.

This building is not "airtight". We can clearly see a hole above the windows under the ceiling.

mental ray in 3ds Max Design for AEC renderings

Smoothing Angles

All 3D geometry--including both edged objects and rounded forms--is made up of polygons. To display them smoothly, 3ds Max interpolates between the surface normals to simulate a rounded form and not a faceted one. When importing a file from another computeraided design (CAD) or 3D application or when working with the Edit Poly modifier, you may find that the information about which normals to smooth by interpolation and which to keep sharp edged with no interpolation can sometimes get lost or corrupted. Instead of reimporting a file or asking your client to resend it, try the Smooth modifier. In most cases, the problems disappear.

32

The cube's faces are smoothed with an angle that's too high, the sphere's faces with an angle that's too low.

This is how the cube and the sphere should look according to smoothing groups.

mental ray in 3ds Max Design for AEC renderings

Flipped Normal

Rendering the face of a geometric shape requires both the vertices that define it and information about its orientation. This can be seen as information about which is the front and which the back of the face, which is done by the surface normal as well. For rendering and lighting analysis purposes, this is critical because light energy will be bounced in the direction of the surface normal.

33

Light is bounced from the direction of surface normals. This is a critical aspect to understand for accurate lighting computations.

When importing a model from a CAD package, you may find that direction information for some face normals gets "lost" or "corrupted". Usually, the modeling package in which the geometry was created may not have provided this information as the entities were created. Use the xView feature to display the face orientation in 3ds Max 2010. If there are only a few faces with the wrong orientation, you can add an "Edit Poly" modifier in 3ds Max Design and use Flip on the affected faces.

The geometry is the same as in the preceding example, but some faces are flipped so they appear to be invisible. Orientation information can be lost or corrupted during import but usually, the modeling program did not taken them into account.

mental ray in 3ds Max Design for AEC renderings

Polygon Count

It is good practice to think about how many polygons an object should consist of before modeling it. This is true for all geometric objects, especially curved and round ones. Each face needs to be rendered, but using many polygons on a round object can quickly add up to inefficiencies, especially if objects are copied within the scene. On the other hand, using too few polygons makes an object appear segmented.

34

Picking a polygon count that is too low for your model gives unsatisfactory results for architectural rendering.

In this example, the bowl's appearance is improved because the shape allows for additional faces without destroying the bowl itself; you could simply add a "TurboSmooth" modifier.

mental ray in 3ds Max Design for AEC renderings

Unwelded Vertices

In some cases, a model might look as if it is closed, but instead each face is separated and the vertices of neighbouring faces are unwelded--that is, not connected. Unwelded vertices can introduce many problems, including large file sizes due to thousands of unnecessary vertices, damage to the object when moving faces or altering the model, and even problems with proper smoothing and normal interpolation, since the faces appear unconnected to 3ds Max. If the "Smooth modifier" doesn't correct smoothing problems, check for unwelded vertices. To weld vertices, simply add the "Weld Vertices" modifier and choose an appropriate radius.

35

Both spheres look the same, but the right one has a row of unwelded vertices. This wastes memory (for example, instancing an object many times) and makes it difficult to modify geometry. Problems appear when moving half the faces with an "Edit Poly" modifier. Welding the vertices corrects the loose edges.

Under certain light conditions you can even see unwelded vertices by studying a render of the object.

Overlapping Surfaces

Watch out for faces that overlap precisely. The renderer cannot determine which one to put in front, and a black pattern artefact will appear. Worse, in the case of lighting analysis, you may end up bouncing more energy than received (double the energy) and get wrong results. Overlapping faces can be introduced by careless modeling or by importing a file, such as a CAD file with versioned geometry overlapping precisely on several layers or by creating a ground plane across your entire model at the same level of the floor finish. Use the xView feature of 3ds Max 2010 to spot them.

Unlike unwelded vertices, overlapping surfaces are easy to spot.

Information

35 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

1324707


Notice: fwrite(): send of 200 bytes failed with errno=104 Connection reset by peer in /home/readbag.com/web/sphinxapi.php on line 531