PREJOIN reads in two or more independently numbered files in NEIGH format and outputs them as a single consecutively-numbered NEIGH format file. There is an option for automatically merging pairs of boundary nodes which lie close to one another. This operation is controlled by specifying triplets of node computational codes (C1,C2,C3) : any node N with code C1 will be merged with the first point M found with code C2, provided that the distance from N to M is less than 20% of the distance from M to its nearest existing neighbour. After PREJOIN has been run, the combined grid should be examined with the Editor to check if all required joins between grids have been made; any further connections required between nodes can be made using the MERGE facility in the Editor, after first turning on the GRIDMERGE option in menu TOP.CONFIG.
In addition to the output grid in NEIGH format, PREJOIN outputs a file PREJOIN.LOG which contains a list of pairs of nodes which have been merged. Since the node numbering referred to in PREJOIN.LOG is that in effect before any merging takes place, it is advisable to do a dummy run with PREJOIN with no merging allowed; the NEIGH file output in that case then has the numbering referred to in PREJOIN.LOG .