Render > Set NURBS Tessellation


Render > Set NURBS Tessellation >

With this window:

Automatic Mode settings

Some of these settings appear and work for the Basic settings of Manual mode also.

Use Frame Range

Available only in Automatic (default) Mode.

The tessellation computed by Automatic tessellation depends on the distance of the surface from the camera. When the surface or camera is animated, this relationship changes over time.

Generally, when the surface is closest to the camera you need the best tessellation (the most triangles). If you know which frame this is, use Current Frame. Otherwise, Maya computes this for you by running up the animation for a specified frame range, evaluates the tessellation at each frame, and sets the tessellation attributes to provide optimal tessellation.

A progress bar at the bottom left of Maya’s window indicates the runup progress. You can also interrupt the runup for the tessellation evaluation by pressing the Esc key. During the interruption, the tessellation values are set and are valid up until the frame at which it was interrupted.

Render Settings

Maya uses the frame range set in Render Settings window.

Time Slider

Use the time slider to adjust the frame range as necessary.

Current Frame

Evaluates the best tessellation for the current frame.

Compute From

Available only in Automatic (default) Mode.

All Renderable Cameras

The default. Computes the automatic tessellation from the point of view of all renderable cameras.

Current View

Computes the automatic tessellation from the current view only.

Curvature Tolerance

You can determine how smooth the nickeling of the tessellation needs to be. When you adjust this setting, Maya automatically sets the Chord Height Ratio (an Advanced setting that is hidden, but automatically sets it in both Automatic (default) mode and Manual mode).

In more complex scenes with many small objects, set the smaller objects to Low Quality. (This table applies only for manual mode; automatic mode sets the chord height, depending on the distance from the camera.)

Low Quality

Chord Height ratio = 0.987

Medium Quality (default)

Some nickeling may occur, but a significantly lower polygon count is produced. Chord Height ratio = 0.990

High Quality

Chord Height ratio = 0.994.

Highest Quality

The result is very smooth edges with no nickeling. Chord Height ratio = 0.995.

No Curvature Check

No attempt to smooth out nickeling is made and only the initial sampling for the tessellation is done.

U Division Factor, V Division Factor

Before adjusting these settings, adjust Curvature Tolerance to get the results you want.

When you adjust this setting, Maya automatically multiplies the values by the Per surf # isoparmsin 3D (an Advanced setting that is hidden, but automatically sets it in both Automatic (default) mode and Manual mode).

The higher the values, the more polygons produced. The U Divisions Factor and V Divisions Factor attributes should contain approximately the same value.

Use Smooth Edge

Use this to increase the number of triangles only along the boundary of an object. This lets you smooth the edges or prevent cracks between shared curves of adjacent surfaces without tessellating across the entire object, which incurs a high rendering time.

The higher the ratio, the smoother the edges and the higher the polygon count.

If you get artifacts in highlights along curved parts of the surface close to an edge, don’t use this attribute.

Smooth Edge Ratio

Adds more triangles where required in areas of curvature along the edges of the surface. The edge is the boundary of the NURBS surface, where one of the U or V parameters takes on its most extreme value. (This does not address the silhouette edges based on how the object is viewed from the camera.)

While extra triangles are primarily added along the edge, some are also added to the interior of the surface as needed to prevent cracking at T-junctions within the surface.

The ratio is the length of the tessellated triangle and the curve of the boundary.

Edge Swap

Helps to divide quadrilateral surface spans into optimal triangles by swapping the two vertices on a quadrilateral used to create triangles. This is a secondary criteria, but it uses minimal resources.

Manual Mode

Select one of the following options:


Basic settings appear when you select this option. For descriptions of these settings, see Automatic Mode settings.

When you adjust Basic settings, Maya automatically sets the Advanced settings (which are hidden for simplicity) as follows (see Advanced Tessellation settings for details):


Advanced settings appear when you select this option. For descriptions of these settings, see Advanced Tessellation settings.

Advanced Tessellation settings

Available only in Manualmode with the Advanced option selected. If you have set the Curvature Tolerance (in either Automatic (default) mode orManualBasic mode) to the highest setting and the object is still not smooth enough, use these settings to have more control over tessellation.

Mode U, Mode V

These are Primary Tessellation attributes (see Primary vs. secondary tessellation passes). These settings tell Maya how to tessellate the surface. The U and V values represent the U and V parametric dimensions of the NURBS surface. You can set these values differently to produce tessellation for each direction of your surface.

Per Surf # of Isoparms

Ignores the number of surface spans and lets you specify the number of subdivisions you want to create. The result is a sparser number of isoparms on the surface than number of spans. Essentially, this setting pretends that everything is equally spaced.

Per Surf # of Isoparms in 3D

Same as Per Surf # of Isoparms, but attempts to space the isoparms equally in 3D space (instead of parametric space). Good for converting NURBS to polygons. This mode produces more evenly distributed triangles than other modes.

Per Span # of Isoparms

This is the most common mode. Divides each span, no matter how large or small, into the same number of subdivisions. Very small spans are divided into the same number of subdivisions as very large spans. The default setting is 3. Per span settings help to prevent cracks between joined surfaces where the spans match, which is particularly important for character building with multiple surfaces.

Best Guess Based on Screen Size

Creates a bounding box around the NURBS surface, projects it into screen space, and calculates the number of pixels in the space. Maya uses this number to guess at the per surface # of isoparms. The maximum value is 40. With this mode, the more screen space the object uses, the higher the value.

This is not good for animation if the camera or the object is moving because the bounding box would change constantly. If the bounding box changes so does the tessellation and texture jitter as a result. (Problems with highlights may occur as well.)


If you have a complicated NURBS surface and have Display Render Tessellation turned on, this setting could delay the update of the display, so be patient.

Number U, Number V

The actual values associated with Mode U, Mode V.

Use Chord Height

Turn on to enable the Chord Height slider value.


Use the Chord HeightorChord Height Ratio orMin Screen option, but not a combination of them.

Chord Height

Chord height is a physical measurement based on object space units; it’s perpendicular distance at the centre of a triangle edge to the curve that defines the surface. If the actual distance measured is greater that the Chord Height value, the triangle is subdivided. Once it is subdivided, it will be checked again against the same criteria and the process will continue until the criteria is met. Chord height is measured in Object Space. The default is 0.1.

Chord Height is based on a default unit and doesn’t always work well for very small models as the chord height values on a small model will be smaller still.

When chord heights are calculated, if any are larger than 0.1, Maya subdivides the triangles and recomputes. This subdivision process continues until all triangles meet this criteria. The smaller the chord height, the better the approximation of the triangle to the surface curve. (This may be useful for industrial designers concerned with the accuracy of a model in relation to a prototype model.)


Do not build models too small. Chord height is measured in Object Space. If you build models on a very small scale and then scale them up, the chord length is always relative to the object, not to World Space, which means tessellation criteria can be very expensive on small objects. For small or scaled objects, select Chord Height Ratio.

Specifies the maximum distance the center of a tessellated span can be from the actual NURBS surface.

Use Chord Height Ratio

Turn on to enable the Chord Height Ratio slider value.

Chord Height Ratio

Specifies the maximum ratio between the length of a span and the distance the center of that span is from the actual NURBS surface.

Takes the ratio between the chord height (d) and the Distance (D) between the two points where the triangle intersects the surface, and subtracts it from 1, as shown in the equation:

Chord Height Ratio = 1 - d/D

A Chord Height Ratio value of 0.997 and above produces very smooth tessellated surfaces. The default is 0.9830, which means d is very small compared to D (for example, 0.9830 = 1 - d/D). The closer to 1, the tighter the fit of the triangle to the surface.(This is best used in animations.)

Use Min Screen

Turn on to enable the Min Screen box.

  • Use the Chord Height orChord Height RatioorMin Screen option, but not a combination of them.
  • Don’t turn on Use Min Screen for surfaces that are moving toward or away from the camera during an animation. Min Screen causes the tessellation to change over time and can cause unwanted displacement or texture ‘popping’.
Min Screen

Bases tessellation on a minimum screen size (default, 14 pixels). All triangles created during tessellation must fit within this screen size. If they don’t, the are further subdivided until they do. This option is good for still images with a setting off 11.0. This option is not recommended for animations because the tessellation will constantly change when an object is moving, causing textures to jitter or jump because the shading for a particular pixel will have different tessellations to deal with on each frame.


If you have a complicated NURBS surface and have Display Render Tessellation turned on, this setting could delay the update of the display, so be patient.

Tessellates a surface based on how far it is from the camera and uses the screen space to determine how much tessellation is required (instead of object or world space).

All triangles must fit within the specified area. The default is 14 pixels, which means all triangles must fit within a 14X14 pixel area on the screen. Triangles that do not meet this criteria are subdivided iteratively until they fall within the specified area. The smaller you set this value, the smaller the triangles must be to satisfy the criteria. Lowering this value can dramatically increase memory, so use caution.

Creative Commons License Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License