In the 3D watershed split plugin, what does the radius setting actually do? Thank you.
The radius will refer to the computation of local maxima to be used as seeds for the splitting, in case there are no seeds image provided. Basically by increasing the radius you will remove close local maxima and then reduce number of seeds, so reducing chance of over splitting. As a rule of thumb the radius should correspond to the approximate size of your object.
You can find basic explanation here.
Hope this helps