The MRC file format. The MRC header, length 1024 bytes, organized as 56 LONG words followed by space for 1080 byte text labels. Header: ------------------------------------------------------------------------------- REC DATA Description ------------------------------------------------------------------------------- 1 NX number of columns (fastest changing in map) 2 NY number of rows 3 NZ number of sections (slowest changing in map) 4 MODE data type : 0 : signed 8-bit bytes range -128 to 127 1 : 16-bit halfwords 2 : 32-bit reals 3 : complex 16-bit integers 4 : complex 32-bit reals 5 NXSTART number of first column in map (Default = 0) 6 NYSTART number of first row in map 7 NZSTART number of first section in map 8 MX number of intervals along X 9 MY number of intervals along Y 10 MZ number of intervals along Z 11-13 CELLA cell dimensions in angstroms 14-16 CELLB cell angles in degrees 17 MAPC axis corresp to cols (1,2,3 for X,Y,Z) 18 MAPR axis corresp to rows (1,2,3 for X,Y,Z) 19 MAPS axis corresp to sections (1,2,3 for X,Y,Z) 20 DMIN minimum density value 21 DMAX maximum density value 22 DMEAN mean density value 23 ISPG space group number 0 or 1 (default=0) 24 NSYMBT number of bytes used for symmetry data (0 or 80) 25-49 EXTRA extra space used for anything – 0 by default 50-52 ORIGIN origin in X,Y,Z used for transforms 53 MAP character string ‘MAP ‘ to identify file type 54 MACHST machine stamp 55 RMS rms deviation of map from mean density 56 NLABL number of labels being used 57-256 LABEL(20,10) 10 80-character text labels ------------------------------------------------------------------------------- Symmetry records follow – if any – stored as text as in International Tables, operators separated by and grouped into ‘lines’ of 80 characters (ie. symmetry operators do not cross the ends of the 80-character ‘lines’ and the ‘lines’ do not terminate in a). Data records follow.