Once a particle has been identified, its location must be determined. In line with the overall philosophy, the approach to determining the position of the particle is relatively simple and is based on the centroid of the particle. There are two measures of this centroid: the area centroid and the volume centroid. The area centroid is the centroid of the area occupied by pixels satisfying the required threshold. The Volume centroid is the projection onto the pixel plane of the centroid of the image exceeding the required threshold.
The value specified in this option places a limit on the difference between these two measures of particle position. If this limit is exceeded, the "blob" to which they apply will not be considered a particle.