Once all individual diffraction patterns have been processed, each
reflection of each pattern is characterized by a duplet of **(h,k)**,
the crystallographic lattice index of the reflection. The integration
step assigned an intensity **(iobs)** and an associated error estimation
**(sigiobs)** to each reflection; a subsequent step used the tilt
geometry to calculate the **z* (zstar)** value as well as its error
estimation **(sigmazstar)**.

The merge process is responsible for first combining reflections from
the individual patterns and then discretizing the irregularly spaced
reflections to obtain a full crystallographic dataset with reflections
organized in **(h,k,l)** triplets. At this point, it is very useful to
think of the combined data as they distribute into lattice lines-
ultimately, it will be those lattice lines which will allow the **z***
to **l** discretization. Generally speaking, each diffraction pattern
contributes to each lattice line, as explained in figure 1. The
merge processing goes back and forth between the lattice line and
individual pattern representation, and thus it is important to
understand how they relate to each other.

The merge process has four distinct steps. In the beginning, reflections from all datasets are pooled, and the crystallographic symmetry is applied. Then, a scaling algorithm takes account of the fact that each pattern is from an individual measurements, meaning that the integrated intensities cannot be just thrown together. Following this step is the tilt geometry refinement, which tweaks the z* values. Finally, the lattice line discretization models the scattered points of each lattice line as a continuous curve, and yields reference reflections at discretized values.

An overview over the merging process is given in figure 2 and a summary of this process from the perspective of a single lattice line is given in figure 3.