This command reads a density map fromfile, which should be provided as a cubic grid of intensities, in the X-PLOR ([Brünger, 1992]) or MRC format. The size of the cubic grid is given byem_map_size. The density map resolution and the map voxel size are given byresolutionandvoxel_size, respectively.

When fitting the probe into the EM grid, the probe structure is converted first into probe density, by using the function indicated in thedensity_typevariable. Each atom can be represented by one of several atomic density functions, including, the uniform sphere model ('SPHERE'), the Gaussian function ('GAUSS'), a normalized Gaussian function ('NORM'), a hybrid Gaussian/sphere model ('HYBRID'), and an interpolation to the closest point on the grid ('TRACE'). The recommended function is'SPHERE'.

filter_typeis used to filter the values of the EM density during this calculation. Filters that can be used are:'THRESHOLD'for a lower threshold (any density value below the first value set infilter_valueswill be set to 0);'SQUARE'for a square filter; and'LAPLACIAN'for a Laplacian filter.'NONE'is the default option, and means that no filter is used.

When calculating the cross-correlation coefficient between a probe model and the density map,ccf_func_typespecifies if you want the normalized cross-correlation coefficient ('CCF'), or the local cross-correlation coefficient ('LCCF').

**Example:** See **density.grid_search()** command.