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This tutorial covers proper modeling and lighting in an interior rendering.

Introduction

You have created an interior model. You click render, the lighting is flat, shadows are lifeless and there are artifacts all over place. the best way to over come this is to setup up your model correctly from the beginning. Also, a very important note about rendering, over 2/3 of the time is in setting your lights up, not in the modeling of the object. So it is best to be patient in getting just the right lighting. Before you jump into this tutorial, it is assumed that you have a basic understanding of Accurender and know where the settings are.

In the following text, AR3 refers to AccuRender v. 3.1.

If you want to use the same AutoCAD models illustrated in this tutorial. The materials for the models can be found in Accustudio MLIB 23. The links are provided below.

  • Tutorial 01 Model (AutoCAD 2000 format)
  • Tutorial 02 Model (AutoCAD 2000 format)
  • Accustudio Materials (models require MLIB 23)


Creating Your Model

There are a few important rules to observe when constructing a model for Radiosity calculation and interior rendering which can be seen in the interior tutorial 01 drawing.

  • Make sure all flat surfaces are continuous. A wall with windows in it is best constructed as a single region so there are no join lines. Plain walls can be 3D faces, thick lines or regions, whichever takes your fancy.

  • Make sure all walls, ceilings and floors meet up exactly rather than overlapping. This will minimize the number of Artifacts occurring at join lines. Cut ceilings and floors round pillars. Don’t worry about details such as skirting, door frames, window frames, coving etc. These will be dealt with later.

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  • Don’t model detail that won’t be seen from the interior viewpoint as it will only slow the rendering down and not contribute anything to the final image.
  • Ideally model window panes as thin 3D faces

Preparing your model for Accurender

Apart from assigning materials to your objects and layers, there are certain object properties that need to be set to ensure that everything renders correctly which can be seen in the interior tutorial 02 drawing. It’s worth mentioning a few words at this point about “Molding and Trim” and “Raytrace Only”:

If you tag an object as Molding and Trim, it won’t cast Radiosity shadows or reflect Radiosity light. It will, however receive Radiosity light. To regain the shadows during Raytracing you must check the Recalculate Lights box.

If you tag an object as Raytrace Only, then it is completely omitted from the Radiosity calculation, neither reflecting nor receiving Radiosity light. This obviously makes the Radiosity calculation faster and avoids unsightly artifacts, however, unless the object is directly lit, it will appear darker as it is not benefiting from reflected light round the room. As a rule of thumb, only use this setting on shiny metal and glass objects.

The decision to include or exclude an object from the Radiosity calculation can be made by answering the simple question; “Will this object make a significant contribution to the distribution of light within the model?”. Be careful though, one chair in a large room may not, but 100 chairs may.

  • Tag everything that is not curved as No Smooth Shading. This ensures that Accurender doesn’t try to “round off” flat surfaces.

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  • Tag skirting, door frames and window frames as Molding and Trim. These are small details which have been placed on top of a large flat surface and have no real contribution to the overall light distribution in the room. Most small objects used to dress an interior should also be tagged.

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  • Tag all chrome and glass objects as Molding and Trim and Raytrace Only. You may be able to get away with just Raytrace Only but there’s no harm in tagging both just to be on the safe side.

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  • Additionally tag windows, window frames and particularly blinds and mullions as Window Covering so that they don’t cast weird shadows from the ambient light coming from outside. Tag window panes as Thin under Type. You can also tag blinds as No Raytrace Shadows if you don’t have direct sunlight coming through the window.

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  • Make sure objects with a directional material applied, such as floor boards are mapped correctly through the Object Properties dialogue box.

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  • Ensure that all objects inserted into your interior such as tables and chairs are Radiosity friendly. For example, a table top should be included in the Radiosity calculation, but the legs should be tagged as Molding and Trim. A glass vase can be tagged as Raytrace Only.

Lighting Your Model

There are hundreds of different options when it comes to lighting, most of which are covered in the Accurender manual. The most accurate simulation comes from Goniometric lights with IES data attached to them which can give you the exact light distribution from a specific light fitting.

However, the main light source in most interiors is the light coming in through the windows and one of the biggest problems can be balancing this with the interior lights.

In the sample drawing interior tutorial 02 there are just two types of light source: Accurender Rectangular lights (600x1200mm) and Daylight.

Basic Accurender lights are very useful for experimenting with as you can change their settings very easily as opposed to Light Fittings which have set values.


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Position your overhead lights a few millimeters lower than the ceiling and tag them as Molding and Trim so as to avoid artifacts. The layer on which you insert your lights should be Black/White in colour otherwise your light source will take on a hue based on the layer colour. Make sure when using grid lights that the mapping origin point of the ceiling lines up with the corner of one of the lights. Set the type and brightness of the light to real world values e.g. 300W Fluorescent.

Daylight Openings simulate the ambient light coming in from outside. They have no settings themselves (apart from being able to obstruct outside light by percentage), they just indicate where the light is coming in from outside. All the settings to do with exterior light are found under the Sun properties.


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Daylight Openings should be positioned outside the window with the center line pointing in. Anything behind the line of the daylight opening will not receive ambient light. Size the Daylight Opening such that it is slightly smaller than the window. If there are blinds in front of the window then alter the Obstructed value accordingly. For large windows it is best to use several smaller Daylight Openings for a more accurate calculation.

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The following settings will make a good starting point for a daytime shot (the results of years of trial and error):

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You may want to alter the Cloudiness setting depending on your background image (see below). For more of a twilight shot simply reduce the Sun and Sky values to 0.05 or thereabouts.

Make sure for the final Raytrace you set Antialiasing to as high as you dare, noise to 0.05 and check Soft Shadows and Recalculate Lights.

Setting the Environment

Many interior renderings are let down badly by the view outside the window, often an inappropriate scene thrown in at the last minute without any consideration for perspective or lighting.

Firstly choose an image that is suitable for the location of the interior with the light coming from approximately the right direction (you can always reverse the image). It may also be desirable to blur the image slightly so it doesn’t dominate the rendering. Also note that most background images will need to be brightened up to create a lighting contrast between interior and exterior.

The image can be placed either with planar, cylindrical or spherical mapping. Planar is the easiest to control as you can see it in the walkabout window before Raytracing and position it accordingly. Always make sure the perspective of the image matches that of your interior view by aligning the horizon lines. One disadvantage, though, is that you will have to keep repositioning the background as you change your viewpoint. Also planar backgrounds don’t reflect in shiny objects in your model, rather they show through the object making it appear transparent.

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Cylindrical mapping is probably the best to use and will reflect in shiny objects. It’s not usually necessary to map it through 360 degrees, 180 is usually more than adequate as can be seen in the sample drawing. Adjust the altitude so that the horizon line of your image is at the correct level.

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Spherical mapping is best reserved for exterior shots and animations as it requires a special spherical image to avoid distortion.

With the image selected and placed appropriately, set the environment background colour to 3 colours which mimic the image. This will ensure you don’t get any horrible cyan reflections in shiny surfaces.

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Final Tweaking

Once you have run your final Raytrace, the fun is still not over. It’s time to hit the exposure controls. Accurender has an auto exposure feature which balances out the overall image sometimes leaving it looking a little flat and lifeless.

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Depending on whether your viewpoint is looking towards the windows or away from them, you will need to adjust the exposure controls to suit.

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There are no standard or suggested values to use as it is purely view dependant. Just remember to use them.

This completes the tutorial.

rev 08.08.2005    ::   For more information visit http://www.accustudio.com/
rev 08.10.2005    ::   Introduction by Daniel Hargreaves

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