Grass Clump

Overview

The Grass Clump object creates a unique clump of grass. The clump is round and the grass is made up of individual blades which are denser toward the center of the clump. While this object might not stand up to close-up scrutiny, it’s good for near-middle to far distances. Note that the surface shader setting is assigned a Default shader with grey colour values at the time the grass clump is created. You will need to change it to an appropriate colour.

Settings

• Name: This setting allows you to apply a descriptive name to the node, which can be helpful when using multiple Grass Clump nodes in a project.
• Enable: When checked, the node is active and the grass clump object will appear in the scene with the settings below applied to its surface. When unchecked, the node is ignored.

• Population mode: This popup has two options:

Individual Object: This is the default for grass clumps created individually, not part of a population. If you choose this option for grass clump objects that are part of a population the population instances will still render but the grass clump object itself will also show up at its original position.
Member of a Population: This is the default for grass clump objects created as part of creating a population. It means the grass clump objects only render as part of a population. If you choose this option for an individual grass clump object it won't render. If you create a grass clump object as part of a population and then decide to use it on its own you may need to change the popup to Individual Object to get it to render.

• Preview mode: This popup has five options to let you choose how the object should be displayed in the 3D Preview, and sets the most detailed mode that the object can be displayed in. The Object Display Mode button in the 3D Preview controls the mode for the preview as a whole. For example, if you set the Preview mode of the object to Wireframe but the 3D Preview object display mode is set to Show as bounding boxes then the object will only be drawn as a bounding box.

• Preview colour: Enabling this parameter causes the grass clump object to be drawn in the 3D preview using the preview colour when the grass clump object display mode is set to Show as bounding box or Show as wireframe. When set to Show as smooth shaded or Show as textured the preview colour tints the grass clump object’s textured surface. This is useful for making a particular grass clump object stand out in the 3D preview. Clicking on the colour swatch to the right of the parameter label opens the Colour Picker pane.

Grass Clump Tab

• Number of blades: This sets the number of grass blades in the clump.

• Clump diameter: This sets the diameter of the clump.

• Blade length: This sets the maximum length, or height, of the grass blades. The blades are given random lengths up to this value.

Surface Shaders Tab

This tab lets you assign a surface shader to texture the grass clump object.

• Surface shader: Use this setting to assign a surface shader to the grass clump object.

• Displacement tolerance: If you find that rough or spikey surfaces are showing problems at bucket edges, for example spikes having cut off tops, or gaps in ray traced shadows then increasing this value may help. However this can greatly increase render times. Relatively flat surfaces may render more quickly with smaller values. The default value is 1. However this is an advanced setting and you should not change it unless you have specific problem you need to address. If you are having problems try starting with 2 and then increase it by small increments until they're resolved. A value of 4 would be considered a high value.

• Smooth polygons at terminator: This fixes self-shadow artifacts at the lighting terminator of polygonal objects where the smooth normals are inconsistent with the geometric normal. This parameter is enabled by default.

• Darken bumps at terminator: This setting approximates self-shadow of bump maps at the lighting terminator to reduce the chance of seeing a sharp line where the surface falls into shadow. This setting is enabled by default.

Rendering Tab

• Render: An object's render state can be set to Visible, Invisible or Holdout. When set to Holdout, an object is visible in the rendered image as a black shape with an alpha value of zero. When using render layers the object's render state is combined with the group visibility parameter to determine its least visible setting. Invisible is less visible than Holdout, which is less visible than Visible.

• Visible to other rays: When enabled, the grass clump object will be taken into account by all the rays determined by the renderer including those from the camera, direct and indirect lighting, etc. In the example below, a 100% reflective 3D object has been placed behind three coloured spheres in order to mirror the effect of the calculated rays.

• Cast shadow: When checked, the grass clump object will cast shadows.

• Double-sided surface: When checked, the grass clump object surfaces are double sided. A single sided surface is only visible from the "front", which is the direction the surface normal is pointing. If you look at it from the other direction the surface isn't visible. Double sided surfaces are visible from all directions.

• Use smooth normals: When checked, the grass clump object normals are interpolated to make the surface appear smooth. When unchecked, its surface will look faceted

• Render method: This popup has three options.

Default: Ray Tracing is the default rendering method for an object. Typically it results in higher quality and faster rendering. When displacement is applied to a 3D object the render method should be changed to Force Displacement. When the object's render method is set to Default, the object is rendered according to the Ray trace objects setting in the render node.


Force Displacement: When enabled for the grass clumpp object, its surfaces will be subdivided into micropolygons at render time, which allows the 3D geometry to be displaced correctly but at the expense of slightly longer render times. It is useful when you have some objects you want to render with displacement but you don't want to change how all the rest of your objects are rendered, i.e. Ray traced.


Force Ray Trace: When enabled for the grass clump object, its surfaces will be ray traced at render time, even if Ray trace objects is disabled in the Renderer settings. This can be useful when Ray trace objects is disabled in the Renderer in order for other 3D objects to use displacement, but you want this object to use ray tracing for the highest quality rendering and it has not been displaced.

• Sorting bias (metres): This setting gives you control over the order in which objects are rendered when using the micropolygon renderer. This does not apply to objects being rendered with the ray tracer. A large positive value, e.g. 10,000,000 (or 1e7) will usually force the object to render first. A large negative value, e.g. -10,000,000 (or -1e7) will usually force the object to render last, or after the terrain. This can be useful when rendering large objects with displacement, such as a lake object that lies mostly below the displaced terrain. By setting the lake object’s Sorting bias (metres) value to something like -10,000,000 forces it to render after the terrain.

Transform Tab

• Translate: This sets the position of the grass clump object.

• Rotate: This rotates the grass clump object about its origin. The order of the values is heading, pitch then bank.

• Scale: This sets the scale of the grass clump object in the X, Y and Z directions.

Angular Position Tab

This tab has settings which use angles and distance to set the position of the grass clump relative to the scene origin. These settings are an alternative to using the Translate setting in the Transform tab. The diagram below shows how all the parameters relate to each other and the origin.

• Heading: This angle sets the rotation of the grass clump object around the scene origin, in the XY plane, increasing as you turn clockwise.

• Elevation: This angle sets the vertical part of the position. You could think of it as the angle above or below the horizon. 90 is straight up, -90 is straight down.

• Distance: This sets the distance of the grass clump object from the origin, in metres.

Import Tab

These settings apply to .chan/.mov and FBX import.

• Import offset: This setting allows you to offset the positions imported from the file. As an example, you might want the positions imported from the file to be moved 10 metres in the X direction. To do that enter 10 for the X coordinate and import the file.
• Import scale: You can use this setting to scale values imported from the file.
• Import chan file: This setting specifies the file to be imported. When you choose a new file you will be prompted to import the file. If you choose not to import it immediately you can click the Import chan File button to perform the import.