MICROSTATION RENDERING: GLOBAL LIGHTING

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Description

Lighting is important to clearly illuminate your renderings in MicroStation V8i. At first sight, the dialog boxes can be daunting, but with a few simple rules you can achieve good results without too many headaches.

Note: with lighting, and rendering in general, it is possible to achieve extremely realistic results with careful setting of your values. For this guide, we will deal with the basics of lighting setup which can normally give very good results. In cases where detailed technical knowledge is required, we will highlight the settings with an “Advanced Alert”.

Default Lighting

To begin, it is a good idea to ignore the complex Light Manager and use the Default Lighting instead. Default lighting uses “hidden lights” built into the dgn file. The results aren’t great, but it is a very good starting point from where you can define your initial materials and set up the scene.

To turn on Default Lighting, tick the box in “Adjust View Brightness”:

Light Manager

Once you have basic materials defined, you can then start to look at setting up proper lighting. Concentrate on getting the lighting right first, although the process will be iterative, as you may need to adjust material definitions as the lighting in your model alters.

Open Light Manager from Visualisation > Home > Lighting > Light Manager dialog launcher (shortcut R 2)

Create a new Light Setup to save and recall your settings by clicking the New Setup icon. If you can’t see the light setups, click the Light Setup List down arrow.

Enter a name for your Light Setup.

Light Manager allows you to set “Global” light sources (sunlight, flashbulbs), as well as adding “Source” lights (spot lights, light bulbs, strip lighting, etc) to your model. In most external situations, global lighting should be all you need. For internal scenes, the closer you can model the exact lighting, the more realistic your results will be.

Global Lights

To turn on the global lights, tick the ON option in each light’s properties.

Brightness

Brightness allows you to adjust the brightness of the image (well, duh). The Brightness settings contain “Display Brightness”, which only affects views that have Smooth display applied to them, and “Global Illumination Brightness” which sets brightness, contrast and gamma correction for rendered images.

The results are pretty self-explanatory. These settings can allow you to quickly and simply change the feel of a rendered image without having to adjust multiple lighting values.

Advanced Alert: Brightness can be adjusted in two ways, using “Brightness Multiplier” and “Adapt to Brightness”. The first option increases or decreases all pixels by the same amount. “Adapt to Brightness” changes the midpoint of the image’s brightness. Imagine a slider moving up and down the Display Range.

Advanced Alert:  Tone mapping adjusts the tonal range by converting the lumen values to a value that a screen can display. Using Photographic Tone Mapping changes the way these values are calculated to make the end result more in line with what the human eye sees. In simple terms, you will get a more realistic range of brightness by having Photographic Tone Mapping on, although unless you are very particular, the differences can be negligible.

Often it is better to leave these settings close to defaults and make any adjustments after generation in image adjustment software (e.g. Photoshop) where greater control can be achieved.

Ambient

This is the “general” level of light in your scene. Used alone it will not give realistic results, but as an underlying addition to your lights it can add light to objects which may not receive enough light. Think of it as the light you would see without any other lights on during a full moon, or the background light of a typical room.

Ambient light does not cast shadows.

Colour: Can be used to set a colour to the ambient light. Be careful when adding colour as your light results can become unrealistic very quickly. Colour can be used to add a stylised look to your rendering.

Temperature: Use this to adjust your colour to approximate a specific type of lighting. Daylight has a colour temperature of 6500K (the setting for 40W Fluorescent lights in Light Manager – i.e. white) although this may vary depending on your location and the time of day. Try values around 5700K for a warmer feel. You can select and option from the drop-down or type in your own values.

Flashbulb

Offers the same settings as Ambient. The main difference being Flashbulb lights the scene from the camera’s eye point.

Low level flashbulb can help bring out the definition of depth and contrast. Too much flashbulb can glare out surfaces directly facing your viewpoint.

Solar

For external scenes, the use of solar light is the most important. It can provide accurate studies of how sunlight will affect your project at any given time of year or day.

Details Tab

As with the other global lights, the Colour and Temperature options are provided. Additionally, you also have:

Shadows:  Turning this option on generates solar shadows. You then have several quality options, from “Sharp” (quick, harsh shadows) to “Soft – Very Fine” which is the most accurate, and slowest, shadow mode.

Note: In low-res previews you may not see any difference in the shadow quality, but don’t be fooled. A good starting point is “Soft – Medium” which should give good results for most every day circumstances. If you need better quality increase the setting up a notch.

Cloudiness: This softens the brightness and contrast depending on the setting. It emulates cloud cover, and how you set it will depend on your time of year and location. For the UK a default start setting would be around 60 (62.5 if you are precise about cloud cover and want to use 5 Octares – ie 5/8th cover).

Air Quality: Represents the haze of the air and affects the solar light, creating hues of colour along the horizon and coloured reflections. For more realistic colours, set a lower value than you would expect. Use Rural or Dry Mountain as a starting point.

Solar Position

Allows you to set your location and orientation in a number of different ways.

We recommend you model using correct orientation wherever possible to make lighting more realistic, although you can reset “North” using the direction setting.

Default is 90° or the Y-axis of your DGN.

Normally set the sun’s position using Type = Time & Location. This will give a true sunlight setting using the date, time and exact coordinates you enter.

You can enter the Latitude and Longitude manually or by using one of the three icons:

“Select Location By City” presents you with a list of major cities.

The UK choices are fairly limited, although additional locations can be added through a text file “globcity.dat” by default located in your C:\Program Files\Bentley\MicroStation CONNECT Edition\MicroStation\Default\Data\ folder.

“Get Latitude Longitude from Google Earth” opens a copy of Google Earth (if it is installed on your PC). Simply pan to the required position and click on it to set the correct location.

Thirdly, you can use a KML file to load the coordinate locations. A KML file stores place markers and can be exported from Google Earth or other similar viewers.

Volume Effects

Volume Effects represent the action of dust particles in the air. The settings here are most obvious when rendering an internal scene where solar light enters the room – through a window or opening.

To add Volume Effects tick the Volume Effects box:

The difference should become immediately apparent.

Without Volume Effects:

With Volume Effects ticked:

The initial result can be extremely harsh, as you can see. The brightness will depend a lot on the level of light in your room – in these examples, the solar light is the only source except for Ambient to clearly show the Volume Effects. To modify the results, you have several controls you can use:

Scatter Colour sets the colour of the dust particles.

Samples improves the accuracy of the Volume Effect. More samples = better results but slower rendering.

40 samples

100 samples

Note: The resolution of your preview will greatly affect what you see. These images were saved at only 400 pixels deep, so the quality of the edges is very approximate, even with a higher sample value.

Scattering is how much the light is dispersed inside the Volume.

Scattering, Density and Attenuation can have very similar effects so use of the three depends on how precise you need to be and the size of your room. Scattering tends to “fade” the light towards the edges of the Volume.

25%

75%

Density represents how dense the dust particles are. A higher value means there is more dust in the air and causes a more opaque result. The difference between this and Scattering can be very subtle. Density is more constant across the complete volume.

25%

75%

Attenuation reduces the brightness of the light throughout the volume; it is a measure of how quickly the intensity fades. The effect will be more noticeable in longer Volumes.

Advanced Alert: Attenuation affects the Volume Effects – the light haze – not the strength of the light itself. To reduce the brightness of the patch of sunlight on the floor, you will need to reduce the Intensity.

Light Shift alters the visible colour of the light that is being scattered as it becomes attenuated. With a small Volume, the effect will be fairly similar to the Scatter Colour, but it will become more marked with a larger room or longer Volume.

Using all settings together can provide subtle light hazing which adds to the subtlety of a render:

Sky Dome

Sky Dome adds light from all directions, emulating the “blanket” of light provided by the sky. Sky Dome offers the same options of Colour Type, Colour, Temperature and Shadow as the other global lights. Sky Dome only adds light into your scene if the Solar light is on and providing light.

It makes the shadows softer and the light more realistic. Normally, for an external scene, you would want to have this on and accept the increased render time.

No Sky Dome

Sky Dome

Advanced Alert: It is possible to achieve less contrasting results for solar shadows without having to use Sky Dome. In the “Expert” tab, change the Shadow Colour setting to a brighter grey. The results aren’t quite as good as Sky Dome, but can be a reasonable compromise for quick renderings.

The same scene as above rendered with R=55, G=55, B=55 shadows. The lighter shadows make a vast difference in contrast between the lit and shaded areas.

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