Diffraction Data Conversion Program
This program performs various operations on density maps and Fourier coefficients. It can convert one form of data into the other and calculate either from atomic coordinates. It can also combine such data from two sources to produce a new map or coefficient file. The data may be either added, subtracted, multiplied, or divided.
The program operates on three different forms of data: Coordinate sets, density maps, and Fourier coefficients. Its purpose is to perform interconversions between these types of data. The conversion between maps and coefficients requires a Fourier transform. The conversion of coordinates to a density map is a straightforward calculation of the density of each atom. The conversion of a map to coordinates returns an atom located at each peak in the map. This is the familiar peak pick operation.
When a map is calculated from coefficients those coefficients are weighted by their figure of merits to produce the ``best" map. If no FOM's are given no weighting is performed.
Most of the work of this program is performed with the PUNCH command.
The Space Groups
When calculating coefficients from a map or set of coordinates all space groups are implemented. This includes space groups with cubic symmetry, centers of symmetry, and mirrors. When calculating a map from coefficients all space groups work except for those which contain mirrors but do not contain centers of symmetry (such as Pm). This means that maps can be calculated in all space groups in which a protein can crystallize.
In all cases rhombohedral space groups must be indexed in the hexagonal setting.