An edge ring is a path of polygon edges that are connected in sequence by their shared faces. An edge loop is a path of polygon edges that are connected in sequence by their shared vertices. Edge ring and edge loop selections let you select several edges across a polygon mesh without having to select each edge individually. For more information see Select an edge ring and Select an edge loop.
A variety of criteria is used for edge loop and edge ring selections. This criteria is also used by the Offset Edge Loop Tool and the Insert Edge Loop Tool. Understanding this criteria can help you troubleshoot an issue when an edge selection doesn’t occur as expected.
Edge rings
In Maya, an edge ring must meet the following criteria:
- The faces that connect the edges must be four-sided (quads).
- The criteria for connecting the sequence is that the next edge in the sequence is the (i + 2nd) edge of the shared face, determined in order from the current edge (i).
- The sequence of edges (ring) can form either an open or closed path on the mesh.
- The start and end edges need not share a four-sided face.
When you double-click to select a ring (path) of edges on the mesh, all adjacent edges in either direction of the initial edge selection also get selected along the same contour line of the mesh. The selection only stops when it cannot determine a corresponding adjacent edge on the shared face or when it reaches the end of the mesh.
Edge loops
In Maya, an edge loop must meet the following criteria:
- The vertices that connect the edges must have a valency equal to four. (Valency refers to the number of edges connected to a particular vertex.)
- The criteria for connecting the sequence is that the next edge in the sequence is the (i + 2nd) edge of the shared vertex, determined in order from the current edge (i).
- The sequence of edges (loop) can form either an open or closed path on the polygonal mesh.
- The start and end edges need not have a valency equal to four.
If you perform a double-click selection and two paths of selected edges appear unexpectedly, this usually indicates that the configuration of the four-sided polygons has one or more faces that are shaped in a diagonal fashion. As a result, the edge selection will deviate by continuing in a different direction. One example of this is when two locator lines appear on a single mesh to indicate that the selection has resulted in a U-shaped selection on the polygon mesh (see diagram below).
