This file is a debugging file that is not used in normal operations. OVERLAPS.TXT is generated by the OVERLAPS subroutine and is specific to a particular landmark. It is read by LITHOS.f and DISCONNECT_LMFILE.f.
This subroutine creates a file OVERLAPS.TXT that LITHOS uses to search for maplets that overlap a given one (LMKNM). It searches a list of maplets in an input list (INFILE). If a maplet has a resolution times lower than LMKNM it is excluded. If the maplet center differs in position by more than twice the sum of its half width and that of LMKNM, it is excluded as well. The remaining maplets are those over which the overlap searches will be made. The input file is generally LMRKLIST.TXT, but this can be very large. In some circumstances, such as when we are dealing with maplets that are completely inside a BIGMAP, a file USED_MAPS.TXT generated by the BIGMAP program that has all maplets used to construct the BIGMAP can be copied into LMRKLISTO.TXT. This will be read as the input file for this subroutine, and it is guaranteed that only maplets in that file should be in OVERLAPS.TXT.
Another important input file which should be read instead of LMRKLIST.TXT is LMRKLISTX.TXT. In the limit of a very large number of landmarks > 20 K, reading the LMRKLISTX.TXT file when you load a landmark into lithos will result in substantial time savings compared to reading the LMRKLIST.TXT file .
(Compiled by JRW)