Here we summarize the steps necessary for joining two existing grids available in NEIGH format.
First, run program PREJOIN, which renumbers the nodes of one of the input grids and outputs the two grids in a NEIGH file as if they formed a single grid. However, the two components (sub-grids) of this output grid are not yet connected to one another.
Secondly, use the Editor, with the output NEIGH file from PREJOIN as input, to stitch together the two sub-grids as required. Some nodes may have to be deleted if the two sub-grids overlap; conversely, extra nodes may have to be added if there is a substantial gap. Connections between nodes of the two sub-grids may be established using {TOP.EDIT}ADDLINE or the node-merging capability available through {TOP.EDIT}MOVE. To use the latter, which is very convenient where there are pairs of adjacent nodes from the two sub-grids, it is first necessary to invoke {TOP.CONFIG}GRIDMERGE (see section on Editor).
When joining grids in this way, it is helpful to begin the editing session with the two sub-grids displayed in different colors. This can be done by suitable choice of the SECONDARY COLOR INDEX , as explained in the description of Editor option {TOP.CONFIG}LINES earlier in this chapter.