map averaging

[ez005078 at othello.ucdavis.edu]

Hi Netters,
    I'm attempting to combine some electon density maps with a program
and
generate a weighted average map. These are from a single structure and
one from a simmulated annealed omit map. The latter has a slightly
different origin and extent, the grids are the same, how can these be
properly processed given these differences. I note that CCP4 has a
program 'extend' that would allow creating an appropriate extend common
to all - does any one know of a program that will transform the origins.

The magnitude of the differences are relatively small ex.
 Grid    =         80        80       640
 Origin  =        -14        -8       -32
 Extent  =        109       101       128

cf
 Grid    =         80        80       640
 Origin  =        -13        -8       -31
 Extent  =        108       101       129

     Any suggestions shall be greatly appreciated, thanks.
                  Joe Maxwell