Rendering SketchUp models with Kerkythea

Quickly creating 3D-models and doing sketchy renderings is clearly the strength of SketchUp. Most of its modeling feature set is even available in the free version and with downloadable Extensions, anything is possible.

One feature that is missing in SketchUp, though, is photo-realistic rendering. But don’t let that stop you…

Kitchen rendering
Kitchen rendering

You can add high-quality rendering to the free SketchUp software even if you don’t have any of the full-featured commercial rendering programs like 3ds max, VRay, maxwell etc. Although there are some commercial rendering solutions available for SketchUp (namely Twilight, Podium, VRay for SketchUp, LightUp, IDX Renditioner, and more – all of these integrate nicely into SketchUp and offer “one-click” rendering. Look at this post for an overview), I suggest you take a look at the freeware Kerkythea. For completeness, it should be mentioned that there are also the free renderers (with export plugins) Indigo and POVRAY, but I (currently) prefer Kerkythea due to its great user interface, fast and great results as well as multiprocessor support.

By the way: Check out my book, “Architectural Design with SketchUp: 3D Modeling, Extensions, BIM, Rendering, Making, and Scripting.” In chapter 5, I describe rendering with Kerkythea (and other rendering software) in more detail.

Kerkythea installs as a separate program and SketchUp models are converted to its XML-based scene description language with a very seamless exporter plug-in (a Ruby-plugin). The rendering engine then provides various rendering methods such as ray tracing, photon mapping, path tracing, BiPT, MLT and also presets for clay and ambient occlusion renderings. It includes a full-featured material editor and additional high-quality materials can be downloaded from the web.

This is a sample image of a SketchUp model rendered in Kerkythea (two light emitting planes, MLT render)

Installation

  1. Download the Kerkythea installer here.
  2. Download the SketchUp exporter plugin and the SketchUp light components here.
  3. Optional: Download Kerkythea sample materials and models (trees etc.) here.
  4. Install Kerkythea.
  5. Close SketchUp. Then install the SketchUp exporter by putting the files into the SketchUp plugin folder (usually C:\Program Files\Google\Google SketchUp\Plugins on Windows). Important: Make sure that you install the plugin files so that the main Ruby file (su2kt.rb) is in SketchUp’s main plugin folder and not in a subdirectory.
  6. Install the light components into SketchUp’s component folder (usually C:\Program Files\Google\Google SketchUp\Components)
  7. Optional: Start Kerkythea and under the File menu, select “Install Library…” to install the material libraries.

Use

The SketchUp exporter download includes a sample file that is very illustrative. It will guide you through scene setup, light creation, modification, animation setup, export and rendering. Go through it and you’ll be up to speed very fast. More tutorials are available here and in their wiki. A very basic workflow goes like this:

  1. Create your SketchUp model. Apply materials and position textures. Textures will be exported and you can refine these materials in Kerkythea’s material editor.
  2. Turn shadows on if you like and/or add Kerkythea light components.
  3. Create animation (formerly tourguide) tabs/views. On export, these will be used to create cameras.
  4. Go to the plugins menu and export the scene. This will create an XML-file and a sub-folder with all the textures. The exporter gives you options to export the selected object only, export the lights or export for a clay render (no textures). Choose as you please.
  5. You can then directly open the model in Kerkythea by clicking OK one more time. If that doesn’t work, revisit the plugin installer documentation. In any case you will be able to open Kerkythea and load the file.
  6. Select a render preset and watch the magic happen. Start with a quick “Photon Map – Quick” preview and work your way up. Also start with a smaller size (800×600 or less). If you have multiple processors in your machine, make sure you use them all as this will speed up rendering.

These are some rendering types that can be done with this software:

Global Illumination:

I used quite “bland” materials here to speed up rendering time. You can set reflectivity or bump in Kerkythea’s material editor.

Ambient Occlusion:

Set the sky color to white or grey, disable the sun and see what happens. Always looks nice.

Image-based lighting (HDRI):

Load a spherical HDR image as a sky image in Kerkythea and you’ll get very realistic lighting conditions.

For far more impressive renderings, check out their gallery.

Tips & Tricks

  • There are two issues with the exporter (SU2KT) that you should be aware of (brought to my attention by “notareal”):
    1. SU2KT sets sun power always to 3.0. After you have opened exported scene go to Settings > Sun and sky > Adjust Sun > Adjust Sky (use physical sky for optimal lighting)
    2. SU2KT uses the so called 0.85 rule with diffuse color because before KT2007 this was needed. Now you can use any color you want, pure white as well, there is no problem in KT with this (look for automatic energy conservation in Patrick’s Material Editor Guide).
  • “Watch your back!” – All faces in SketchUp have front and back sides. Make sure you clean these up (switch all visible sides to front) in SketchUp before you export.
  • SketchUp objects usually have a very low polygon count, which may lead to spheres looking a bit “edgy”. To fix this, highlight the object in Kerkhythea, right click on the material/object in the list, under “Modelling” click on “Weld Vertices” and then let it subdivide the mesh (“Loop Subdivision”) for you.
  • Objects are exported from SketchUp “By Material”. I.e. separate objects in SketchUp by assigning different materials to them. These can simply be different colors, of course.
  • As with any renderer, a large number of reflective and refractive materials (glass, metal, etc.) significantly increase rendering time. Sometimes it may be enough to just use one of SketchUp’s “corrugated metal” textures and rather postprocess the image in Photoshop. Also, depth of field increases rendering time significantly. If you need to have blurred backgrounds, render a depth map in Kerkythea (one of the last settings) and add DOF in Photoshop.
  • Keep light emitting objects simple (i.e. use rectangles only). The higher polygon count of more complex objects will slow down any render.
  • One great tip for Kerkythea materials that I found on the forums: To create a good-looking material, apply one of the basic plastic materials (with the desired reflectivity) and then apply your texture to the diffuse channel.

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