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Homemade skydomes

Dave Donley

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  • Vectorworks, Inc Employee


See the attached file, this is a colored 3D polygon, a two color RW background, and a rectangle that is twice as wide as it is high. Using the File->Export HDRI menu item, you can create homemade colored skydomes with this file.

1. Open the attached file, it should render in FastRW mode (there are three layers with differently-colored backgrounds and ground planes).

2. Choose File->Export->Export High Dynamic Range Image (HDRI).

3. Choose the marquee option, then click the Draw Marquee button.

4. Snap the mouse to the upper left and lower right corners of the guide rectangle to define the marquee as twice as wide as it is high. Click Save. Give the exported EXR file a name.

5. For a 3D model, create a new RW background resource, choose Image Environment (HDRI) from the background popup, and import the EXR file to define a colored sky dome for your rendering.

Note that this is a low-dynamic-range image not HDRI. The background may look dark if you render this with a bright directional light (like thousands of lux). It can be useful to lower the color saturation in the edit RW background dialog, so that the lighting is not overly colorful.

Edited by Dave Donley
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  • Vectorworks, Inc Employee

It will export as deep an image as was rendered, but since the image doesn't really push the pixel values above RGB (255, 255, 255) then it is effectively not high dynamic range. It is "regular" dynamic range. If you overlit the scene then the HDRI export will export those >255 pixel values.

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  • Vectorworks, Inc Employee

Hi again Nicholas:

The thing that makes an image "high dynamic range" is that the pixel luminances are greater than 1, allowing the image to store the full tonal range that one could see in the real world.

To produce a high dynamic range rendering in RW you would just need to provide lighting in the model that would render as a wide range of values. One example could be sunlight coming in to a mostly-dim room.

Note that the low values are part of the range too - since the HDRI stores pixel values using real numbers instead of integers then the difference between red=0.21 and red=0.23 is also maintained in the image. Visually this means that objects in dim parts of the rendering still have their full detail available if you were to brighten up the image to see them better.

Edited by Dave Donley
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  • Vectorworks, Inc Employee

Hello MikeB:

Both. With just the HDRI it would give an even light, like for an overcast day. With a directional you would have both sun and sky.

A dome is also useful not just for sky but for say a plain white lighting that enhances depth for a studio-type rendering.

With final gather in 2008 it is more efficient using HDRIs for sky light coming through windows than to use area lights inside the window frame. So for a daylight interior you only need the skydome HDRI and a directional light and you're ready to render with final gather.

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