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PGW world file contains coordinates which terrain builder reads and automatically aligns the imported satellite tiles into correct coordinates.
Global mapper file → export raster/image format, normally with “create world file” option, it creates a PGW for each tile like sat_A1.pgw, sat_A2.pgw etc.
2 0 0 -2 200000.5 33791.5
First and fourth lines is meters per pixel (dunno why fourth is negative), last two lines are the terrain builder coordinates.
You can also create PGW files manually in proper text editor for example if you import L3DT or other source satellite tiles.
2019-01-20 This worked OK with 40960 resolution satellite on 4 x 4 tiles, but did not work on 5120 or 81920 resolution satellites for some odd reason.