[0,1]$, such that the drawing at time $t=0$ is $\Gamma_0$ and the drawing at time $t=1$ is $\Gamma_1$. A morph is usually required to preserve a certain drawing standard and pursues certain qualities.

The *drawing standard* is the set of the geometric properties that are maintained at any time during the morph. For example, if both $\Gamma_0$ and $\Gamma_1$ are planar drawings, then the drawing standard might require that all the drawings of the morph are planar. Other properties that might required to be preserved are the convexity of the faces, or the fact that the edges are straight-line segments, or polylines, etc.

Regarding the *qualities* of the morph, the research up to now mainly focused on limiting the number of *morphing steps*, where in a morphing step vertices move along straight-line trajectories at constant speed. A morph $\mathcal{M}$ can then be described as a sequence of drawings $\mathcal M=\langle \Gamma_0=\Delta_0,\Delta_1,\dots,\Delta_{k}=\Gamma_1\rangle$ where the morph $\langle \Delta_{i-1}, \Delta_i \rangle$, for $i=1, \dots, k$, is a morphing step. Following the pioneeristic works of Cairns and Thomassen [@c-dprc-44; @t-dpg-83], most of the literature focused on the straight-line planar drawing standard. A sequence of recent results in [@DBLP:journals/siamcomp/AlamdariABCLBFH17; @DBLP:conf/soda/AlamdariACBFLPRSW13; @DBLP:conf/icalp/AngeliniLBFPR14; @DBLP:conf/compgeom/AngeliniLFLPR15; @DBLP:conf/gd/AngeliniFPR13] proved that 