Hi Pascal, The map data is a three dimensional array with dimensions [NC, NR, NS]. On its own, this gives you no information about the grid pitch in the three (crystallographic, not Cartesian) directions, which is determined in fractional coordinates by the number of intervals. That is, along the X direction the sampling interval has size 1/NX. Of course, you need the X, Y and Z lengths (elements 11-13) to convert the fractional coordinate sizes to real space units. There is a further conversion to take into account too: the correspondence between X, Y, Z and C, R, S is not fixed by the format, but is file dependent and described by MAPC, MAPR and MAPS (elements 11-13).
Hope this helps, -- David On 15 September 2011 08:30, Pascal <pascal...@parois.net> wrote: > Hi, > > I am looking at the specifications of the ccp4 map file format and I am > confused with the number of columns and the number of intervals. > > I assume that the number of columns is the grid size but what is the > number of intervals (elements 8-9 in the header)? > > Regards, > Pascal >
