Quads, Tris & N-Gons

When modeling in 3D with polygons, it is important to construct all of your models using quads and triangles.


Triangular Poly (3 Sides)

Triangular Poly (3 Sides)

A triangular polygon is referred to as a tri or triangle, and is a simple three-sided polygon. It has exactly 3 vertices at its corners and 3 edges connecting those points. This is the smallest configuration required to make a polygonal face. 

A Quadrilateral Polygon (4 Sides)

Quad Polygon (4 Sides)

A square or rectangular polygon is referred to as a quad or quadrilateral polygon, and is a four-sided polygon. It has exactly 4 vertices at the corners connected by 4 edges. This is the most desired type of polygon when creating digital models, and many artists like to build their objects using nothing but quads to help make their work more appealing to customers in complex pipelines. 

NGon Poly (<4 Sides)

N-Gon Poly (More than 4 Sides)

An N-Gon is a polygon with more than four vertices and edges. This kind of polygon is not desired by TurboSquid customers and should be avoided. Due to its geometric properties, an N-Gon can always be divided into quads, tris, or a combination of the two; so they are always easy to remove by adding connecting edges between the border vertices.

For CheckMate Pro certification (2.2.1), your model’s topology must be quad-based with no more than 10-15% tris used. To be certified, your model may not use any n-gons.

Why N-Gons Should Be Avoided


Difficulty when subdividing

  • N-Gons subdivide poorly and produce unwanted topology, even on flat surfaces. While it may be quicker to model using N-Gons, it is a bad habit to get into as they disrupt the edge flow of your model, making selection of edge loops more difficult. Having N-Gons often leads to strange rendering or smoothing artifacts that are hard or impossible to eliminate. Instead of leaving N-Gons around in your model, it is better to avoid them altogether since quads and tris will always subdivide properly.

Ngons (in red) don't subdivide cleanly

Yuck! Ngons (marked in Red) don’t subdivide cleanly or predictably


Unwanted behavior when importing and exporting

  • Some applications do not handle N-Gons well or at all. Popular sculpting products like ZBrush, Mudbox and 3D Coat will bring up alert messages when an artist tries to import a model with N-Gons present, and sculpting across those surfaces will produce unwanted results. For customers, Ngons can cause major issues when trying to use your model in multiple environments and as such, need to be avoided.
NGons in 3ds Max -- Unable to Sculpt cleanly in Mudbox

NGons in 3ds Max  —  Unable to Sculpt cleanly in Mudbox

How To Identify N-Gons In Your Models

Select the model.

  1. Go to the Modifier tab in the Command Panel and select the Editable Poly modifier.

If Editable Poly is not available within the existing Modifier Stack, apply an Edit Poly modifier from the modifier list at the top of the stack.

  1. Within the Editable Polygon modifier, enable the Polygon Sub-Object mode (denoted by the red square). You can also hit the 4-key to activate Polygon Sub-Object mode.
Poly Sub-Object Mode

Poly Sub-Object Mode

  1. The Graphite Modeling Tools Ribbon will activate below the menu sets. Within the ribbon, choose the Selection tab
Ribbon Tabs

Ribbon Tabs

  1. At the end of the Selection tab is an option to select By Numeric. Input 4 for sides, click the Greater Than symbol (>) and click the arrow button to the right to execute the selection
By Numeric Settings

By Numeric Settings

Any n-gons will become highlighted in red on the selected model as shown below. Once identified, you can now fix the n-gons so they are converted into quads and tris.

N-Gons highlighted in red

N-Gons highlighted in red


Before you start, make sure you have no actively selected faces on the model you want to inspect.

  1. Go to the Polygons menu set (or the Modeling menu set in Maya 2016 or later).
  2. Click Mesh and then select Cleanup…
  3. When the Cleanup dialog appears:
  4. Within the Cleanup Effect section:
    • For Operation choose Select matching polygons
    • For Scope choose Apply to all polygonal objects (Note: if you only want to check a specific object or set of objects, select them first, then choose the Apply to selected objects option for Scope instead)
    • Ensure the checkbox for Keep construction history is enabled
  5. Within the Fix by Tesselation section:
    • Enable the checkbox for Faces with more than 4 sides
Maya Cleanup Dialog

Maya Cleanup Dialog

  1. Click Cleanup or Apply and Maya will locate any n-gons within your model and highlight them.
Maya_Ngons_with_Menu

N-Gons highlighted on Cleanup

Once identified, you can now fix the n-gons so they are converted into quads and tris.

There are a couple of ways of identifying N-Gons inside of CINEMA 4D

Option 1:
  1. Select your model and go into Edge or Polygon mode
  2. Above the main modeling viewport, select Filter and check the option N-gon Lines

If N-gons exist within your model, CINEMA 4D will create highlighted edges with a greenish (default color) line as a suggestion of how to eliminate them as shown below.

CINEMA 4D Filter Option for N-Gons

CINEMA 4D Filter Option for N-Gons


NOTE:
The default color for the N-gons lines is a bit subtle by default, but can be altered by going to Edit -> Preferences -> Scheme Colors -> Editor Colors -> N-gon Lines to make it a bit more obvious.
Option 2:
  1. Select your model and go into Polygon mode.  This mode will ensure that N-gons are highlighted.
  2. From the main CINEMA 4D menus, choose Window -> Structure Manager. By default, Structure Manager is docked on the right of the Objects window.
  3. In the Structure Manager window, select Mode -> N-gons.
Structure Panel Modes

Structure Panel Modes

The structure panel will update and list polygons by the number of vertices they have. Larger polygons will rise to the top by default. By selecting polygons with more than four points (P5 column and up) C4D will highlight where N-gons exist as shown below.

N-Gons Selected via Structure Panel


Finding N-Gons in Lightwave Modeler is very simple.

  1. Deselect all of the polygons in your model.
  2. Hit the W-key to bring up the Model Statistics panel.
  3. If necessary, hit the Space Bar until you see the Polygon Statistics show up.
  4. Look for the >4 Vertices row. If you see a number greater than 0 listed next to this entry, it means you have N-Gons in your model. To see them, click on the + sign next to the >4 Vertices text.
LW_NGons_Selection

Polygon Statistics for N-Gons

At this point, all N-Gons in your model will highlight and you can go in a repair them, converting them to quads and triangles.