Rendering grass and other organic 3d objects like trees, and plants into your scenes will often bring your rendered images to the next level of realism. It is generally not feasible to place every blade of grass in your 3d scene and thankfully there are a couple of Sketchup plugins around that automate this process for you. The one that I have used every now and then is called Make_Fur which is available for free from the Sketchucation plugin store. To download it you simply need to create an account with Sketchucation, download their plugin store extension and then find Make_Fur from their list and click install.
It then becomes a matter of creating a grass component, either some grass shaped geometry or a PNG photo of some grass blades with a transparent background (removed in an image editor) and then using the plugin to randomly place the component on a designated face. You can see by the results in the image below, created from a long grass variety with seed-heads, that it works very effectively and there are options in the plugin to randomise the scale and lean of the grass blades to create a more natural look. You can download this Sketchup model from the download files link at the top of the article.
The problem with this particular plugin (and the plugin author fully acknowledges this) is that it places a vast number of polygons into your 3d model. The grass components need to be quite dense in order to cover the ground surface and when you suddenly add 100,000 odd polygons in the form of grass blades into your model, it will reduce Sketchup’s performance to a slow crawl on even the fastest computers. While layering your model carefully will help, the effect on performance will see most people put adding realistic grass into their renders into the too-hard basket and opt for a less convincing 2d texture map or doctor their finished renders with a photograph of some real grass taken from approximately the same angle.
An alternative to Make_Fur is a commercially available plugin for Sketchup called Skatter. Skatter is an amazing plugin that considers all the problems of rendering huge numbers of polygons and then conveniently bypasses Sketchup’s interface so that these polygons only show up when activated in the rendering engine. What this means is that you can have vast grassy fields or forests of trees in your rendered images but with little or no effect on Sketchup’s performance. If you do a lot of rendering, this feature alone is well worth the money. Before I get carried away though, it should be noted that not every rendering engine supports this function; thankfully Twilight Render is supported so anyone who has done my Sketchup For Visualisation short course or intends to in the future can use this plugin to full effect.
As well as this important feature, Skatter has many other options to optimise your models so that you are not rendering your grass components unnecessarily. For example when creating a field of grass, you can set a fall-off rate so that grass blades are less dense as you get further away from the camera. You can set the grass field to match your camera’s cone of vision so that it does not generate grass outside of your scene. There is a lot of control over your Skatter components and you can layer up multiple types of grass or vegetation so that there is a considerable variety of foilage in your scenes, changing the scattering parameters such as scale, rotation, density to ensure there is enough coverage of your base surfaces. You can even concentrate your grass blade density around the borders and edges of pavements where you often need extra grass blades to hide the ground surface underneath. I did find that my best computer which I use for rendering did at times struggle with some of the preview generations and would occassionally hang, but in general, the plugin appeared to be pretty stable; the most important feature in any piece of software!
And it is not just about grass either. You can use either of these plugins to create leafy vines on walls, a forest of trees, street lights around roads, fields of pebbles or rocks, even shagpile carpets just to give you a few ideas. Whatever you attempt to render, like anything it requires a bit of fiddling with the settings and component textures to get it right. You can see my efforts on this page to create a lush green lawn and an abandoned railway scene with dry yellow grass and rocks with the plugin.
To sum up, while it does require a bit more effort to get photorealistic grass into your 3d renders, it is definitely achievable with Sketchup and you can get some amazing results with Skatter, Make_Fur and the many 3rd party rendering engines that are available.
You can download a 15 day trial or purchase a licence for Skatter from here: http://getskatter.com/