Tessellation and Approximation

NURBS surface, poly, and subD tessellation

You don’t need to adjust tessellation for polygon meshes or subdivision surfaces unless those surfaces are displacement mapped.

A NURBS surface is composed of one or more patches. (For more information on NURBS surfaces see Degree of NURBS curves and surfaces in the NURBS Modeling guide.) During rendering, each patch is divided into an appropriate number of triangles to approximate the true shape of the surface.

You can set NURBS tessellation on all or selected objects (see Render > Set NURBS Tessellation on page 327), or on an individual basis by selecting an object and adjusting the settings in the object’s Attribute Editor.

Tessellate NURBS surfaces

View Maya tessellation settings for an object

See Primary vs. secondary tessellation passes on page 40 for information on Maya’s default tessellation settings.

To view Maya tessellation settings for an object

1 Select the object whose tessellation settings you want to view. 2 Open the Attribute Editor (CTRL+a).

3 Click the shape tab (for example, nurbsSphereShape1). The shape node’s attributes appear.

4 Expand the Tessellation section.

Adjust NURBS tessellation settings

NOTE Some of the advanced tessellation parameters can dramatically increase rendering times.

Because the tessellation of NURBS surfaces has nothing to do with the material assigned to the surface (unless the surface is displacement mapped), you can start adjusting tessellation early in the process, anytime after the object is modeled.

To adjust tessellation on NURBS objects

1 Determine which objects in the scene you have to adjust tessellation settings.

See Determine which objects to tessellate on page 43.

2 Display the tessellation triangles so you can visualize your adjustments. See Display NURBS tessellation triangles on page 43.

3 Select the object(s) for which you want to adjust tessellation. If you want to apply settings to All surfaces, skip this step.

4 Select Render > Set NURBS Tessellation > to open the Set NURBS Tessellation Options window.

5 Choose either Selected Surfaces or All surfaces (see Selected Surfaces, All Surfaces).

6 Switch the Tessellation Mode from Automatic (default) on page 328 to

Manual on page 328.

(You can also adjust some of the Automatic tessellation settings to optimize the default settings. See Automatic Mode settings on page 328.) 7 Select either Basic on page 330 or Advanced on page 330 tesselation.

Always start with the Basic settings. Basic lets you adjust a smaller number of settings that automatically determine some of the more advanced settings.

NOTE Some of the advanced tessellation parameters can dramatically increase rendering times, so choose them wisely.

8 Test render to see the results.

Fine-tune the adjustments you’ve just set until you reach an adequate level of smoothness.

TIP To prevent overtessellation of objects, use the Use Smooth Edge on page 330attribute in the Render > Set NURBS Tessellation on page 327 window to increase tessellation only along the edge of the object.

Determine which objects to tessellate

What models are going to be used are usually determined during the pre-production phase of a project. Based on storyboards, you will know their positions in the scene and distance to the camera.

Determine which objects never get close to the camera and which ones either are (for static images) or do (for animated objects).

■ If an object is far from the camera at all times, decrease the default settings. ■ If the object is middle distance away from the camera, leave the default

settings.

■ If the object gets close to the camera at some point during the scene, increase the tessellation settings a little more, but only enough to achieve an acceptable level of smoothness.

Display NURBS tessellation triangles

1 Select the NURBS surface(s) you want to see.

2 In the Tessellation section of the NURBS object’s Attribute Editor, turn on Display Render Tessellation.

Use span-based tessellation

1 In the Tessellation section of the surface’s Attribute Editor, turn on Enable Advanced Tessellation and set Mode U and Mode V to Per Span # of Isoparms. Guidelines are as follows:

To use span-based tessellation

1 Turn on Smooth Edge. Open the Common Tesselation Options section of the Attribute Editor to access the Smooth Edge check box.

Tessellate polygonal surfaces

Adjust polygonal tessellation

To set polygonal tessellation

1 Select the polygonal object for which you want to set tessellation. 2 Click Window > Attribute Editor, in Tessellation Attributes section to

adjust the attributes.

Tessellate subdivision surfaces

Display subdivision surface tessellation triangles

1 Select the object.

2 Click Modify > Convert > Subdiv to Polygons to convert the subdivision surface to a polygonal surface to use as a temporary visualization object.

Adjust subdivision surface tessellation

1 Select the subdivision object for which you want to set tessellation. 2 Click Window > Attribute Editor, in Tessellation Attributes section to

adjust the attributes.

Visualize and render

images

Rendering methods

Interactive Photorealistic Rendering (IPR)

IPR is available only for Maya software rendering and mental ray for Maya rendering.

IPR, a component of the Render View rendering, lets you preview and adjust lights, shaders, textures, and 2D motion blur quickly and efficiently.

IPR is ideal for visualizing your scene as you work because it almost immediately shows the changes you make. You can also pause and stop IPR rendering and select several rendering options to be included or excluded from the IPR process.

4

IPR works a little differently than regular software rendering; if you need to know more about how it works, see How IPR works on page 48.

IPR doesn't support all software renderable features (for example, raytracing or production quality anti-aliasing are not supported). See IPR Limitations (for Maya software renderer) on page 49.

How IPR works

When you start an IPR session, Maya computes the initial IPR image, which is a deep raster format that contains more than just the final picture. Maya performs all the visibility calculations (only once), and stores the results in a file in the iprImages directory.

An IPR image is an IFF image with additional data. It is larger than a regular image file because it stores both visibility and shading data. The data is computed in the following ways:

■ Visibility calculations compute where items are located in the scene, or what is visible to the camera (or to the light, for depth maps for shadowing) at each pixel in the image.

■ Shading calculations compute what color is displayed at each pixel of the image.

NOTE An IPR image is not part of the scene file; it only represents what the scene looks like from a specific camera or light, at a specific time. You can reuse an IPR image as you work on the scene, but remember that the IPR image may be out of sync with the scene as you adjust it and move objects in the views.

The data in this format is used to efficiently adjust shading and lighting parameters in an interactive way.

To adjust IPR options, see IPR Options on page 402. NOTE For advanced users:

You can batch process IPR images ahead of time from the command line, so you can then adjust several frames of the same animation, in which the visibility data may vary from frame to frame.

See To batch render IPR files on page 125 for details.

It takes longer to perform an IPR render than it does to perform a software render because more information is written to disk. The IPR image contains