An .prm file is an ASCII file which serves as an input file for the ImageD11. The code below shows an example of how a basic .prm file looks like. Explanations are below.

cell__a 4.6610146
cell__b 4.770392
cell__c 6.634218
cell_alpha 90.0
cell_beta 90.0
cell_gamma 90.0
cell_lattice_[P,A,B,C,I,F,R] P
chi 0.0
distance 551262.3
fit_tolerance 0.05
min_bin_prob 1e-05
no_bins 10000
o11 0
o12 -1
o21 -1
o22 0
omegasign 1.0
t_x 0
t_y 0
t_z 0
tilt_x 0.0
tilt_y -0.00226359983579
tilt_z 0.00381198553699
wavelength 0.2898
wedge 0.0
y_center 1072.82326716
y_size 200
z_center 1017.08073998
z_size 200
cell_sg 62

Information in the prm file are

• Cell parameters: cell_a, cell_b, cell_c in Angstrom; cell_alpha, cell_beta, cell_gamma in degrees (typically taken from Maud refinement and can be refined using ImageD11)
• Lattice type: P = primitive, F = face-centered, A = A-centered, …
• Distance = sample-detector distance in µm (typically taken from Maud refinement and can be refined using ImageD11)
• O-matrix (check the concept of the O-matrix if you are not sure)
• Omegasign = rotation direction (1 = clockwise, -1 = counterclockwise)
• Tilt: Be careful with this one: Tilt in ImageD11 is sometimes not the same as tilt in other software! (usually keep 0 and refined later using ImageD11)
• Wavelength in Angstrom
• y_size, z_size: size of one pixel in y direction and z direction in µm
• y_center, z_center: pixel coordinates of the beam center (usually taken from Dioptas calibration: y_center = Dioptas Center X and z_center = 2048 - Dioptas Center Y and can be refined using ImageD11)
• Supplementary optional parameter cell_sg. You can also provide your material space group. This has to be done manually with a text editor and can not be done using the Graphical User Interface. If the space group is provided, ImageD11 will use xfab for generate unique hkls.