Re: [ccp4bb]: Big Endian vs Little Endian for CCP4 Map Files

["David J. Schuller" <djs63@cornell.edu>]

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On Sun, 27 Oct 2002, Ashwin.Padmanabhan wrote:

> Am facing a problem as with reading the map file generated by the FFT
> program.  Neither my code or the Swiss PDB viewer is able to read the CCP4
> map format generated by the FFT program.  Apparently the Map file generated
> is of the Little Endian format while my code or Swiss PDB expect Big Endian
> formats.  Is there a field in the CCP4 file which tells me whether the file
> is in Little Endian or Big Endian.  I have come across both kinds.  Any
> suggestions as to how to address this problem??

Yes, there is a field in the file header which specifies Big-endian vs. 
Little-endian.  I take it "your code" does not use the CCP4 subroutine 
libraries to read the map file?  Endian recognition should be automatic.
You can read about this in $CDOC/libfft.doc and find the subroutines in 
$CLIBS/maplib.f

One solution would be to run a genuine CCP4 program on the map file on the 
target machine, to force output to the appropriate endian-ness. Something 
like MAPMASK or EXTEND might do it.  A CCP4 program reading a map should 
recognize and read the Endian-ness of the input map, and should write the 
output map in the native mode of the machine you're running on.

cheers,

=======================================================================
"Being a true scientist, Ralph wanted to make his own dangerous experiments."
                                                      - Hugo Gernsback
=======================================================================
                        David J. Schuller
                        modern man in a post-modern world
                        MacCHESS, Cornell University
                        djs63@cornell.edu