Spatial binning
This modifier generates a 1, 2 or 3dimensional grid covering the simulation domain and assigns each particle into one of the uniformly sized bins. It then performs a reduction operation for a selected particle property, mapping the values of all particles contained in a cell to a single output value. This modifier can thus be used to project the perparticle data to a structured grid, for example to coarsegrain the atomistic data and generate a continuous field representation of a particle property. You can choose between different reduction operations, e.g. sum, average (mean), minimum or maximum.
The bin grid can be one, two or threedimensional, i.e. the simulation domain can be subdivided into equally sized bins along one, two or all three of its axes. The spatial bins are always aligned parallel to the simulation cell edges.
Data output options
When mapping the particle values to a onedimensional bin grid using this modifier, you can subsequently access the computed data series in the data inspector panel. From here you can export the bin values to a text file.
When mapping the particle values to a threedimensional grid using this modifier, you can subsequently employ the Create isosurface modifier to render isolevel surfaces of the computed field.
When creating two or threedimensional grids, you can also export the computed grid data to a text file using OVITO's file export function. Pick the "VTK Voxel Grid" format as the output format.
Parameters
 Input property

The source particle property the reduction operation should be applied to.
 Use only selected elements

Restricts the calculation to the subset of particles that are currently selected.
 Binning direction(s)

This selects along which axes of the simulation cell the bins are created and determines the dimensionality of the generated grid.
 Number of bins

Number of bins in each active binning direction.
 Reduction operation

The type of reduction operation to be carried out. Available are sum, mean, min or max. There is an additional option "sum divided by bin volume", which sums over all particles of a bin and then divides the result by the volume of the bin. This option is intended to compute pressure (or stress) within bins from the peratom virial.
 Compute first derivative

Numerically computes the first derivative of the binned data using a finite differences approximation. This works only for onedimensional bin grids. (It is useful to e.g. compute the derivative of a velocity profile to obtain the local shear rate.)
 Fix property axis range

If selected, the plotted property range (or color scale for 2D grids) will be set to the values given in the "From:" and "To:" fields. Otherwise, the minimum and maximum data values will be used to automatically adjust the plotting range.
Acknowledgment
The code for this modifier has been contributed to OVITO by Lars Pastewka.