FME Form: 2024.1

# Triangle Strip

A triangle strip is a series of connected triangular faces. These faces are defined by three consecutive points in a point list. The first triangular face contains the first three vertices, denoted below by v_{1}, v_{2}, and v_{3}. A new triangle is formed by connecting the next point with its two immediate predecessors. That is, every additional point v_{i} defines a new triangular face containing vertices v_{i-2}, v_{i–1}, and v_{i}.

For example, the second triangle contains v_{2}, v_{3}, and v_{4}, the third contains v_{3}, v_{4}, and v_{5}, and so on. The following diagram illustrates a typical triangle strip:

In order to maintain a consistent orientation, each successive triangle is defined with opposite orientation. In the diagram above, the vertex order would be (v_{1}, v_{2}, v_{3}) for the first triangle, (v_{4}, v_{3}, v_{2}) for the second, (v_{3}, v_{4}, v_{5}) for the third, and so on. Due to this propagation, the overall orientation of a triangle strip can be determined by the orientation of the first triangle.

For information on how vertex order affects surface normal and front/back surface determination, see Faces. As a consequence of this, some triangle strips can only be directly defined in one direction and cannot be reversed without adding additional geometry under the default right-handed coordinate system (counter-clockwise winding order). In particular, triangle strips with an even length cannot be directly reversed. To mitigate this, triangle strips also store a flipped flag which defines whether the strip should use a left-handed coordinate system (clockwise winding) instead of right-handed.

Triangle strips may store measures on their nodes.

Triangle strips may possess optional front or back appearances, and may be single or double sided.