You must read an existing SNAP input file to initialize the SNAP\ input variables. SNAPIN will start you off in the Read Input File submenu so that you can read an old shot-try or a SNAP input file of an arbitrary name:
<0=MO> Option for SHOT 51032 @ 3.470 s? <Sh>: RE <1=F> Read from File or Shot-try? <F>: RETURN \* Options are: 1) File 2) Shot-try <1=F> Read from File or Shot-try? <F>: S <2> Shot and try? <51032>: 58505 <3> Try? <1>: 3 TFTR$AW3::[SNAP.TFTR.1065]058505_003.NAME;1 read. or <1=F> Read from File or Shot-try? <F>: F <2> File? <SNAP.DAT>: SNAP.DAT.43 GIBNEY$:[SNAP]SNAP.DAT;43 read.(Note that if you specify a version number in the input file name, precede it with a period instead of a semicolon.)
Whenever you read a file or a shot-try from the archives, SNAPIN\ first reads the HLDAS$:[CURRENT]SNAP.INI file to reset certain standard physics parameters. These are described in Sections 3.4 and 3.8.