OptionalcallbacksFallback collision radius, in px, used only for nodes that report no circle radius. Nodes with a radius use d3CollideRadiusMultiplier × their radius.
Multiplier applied to each node's circle radius to derive its collision radius (the spacing the sim keeps between nodes). Higher spreads nodes further apart. This is what the "collision radius" physics knob scales via Simulation.setCollisionRadius.
Centring pull toward the canvas centre, applied only to isolated (degree-0) nodes so they don't fly off; connected nodes use d3GravityStrengthConnected.
Centring pull for connected nodes. Kept low by default so link + charge forces find their own equilibrium; raise it to stop a sparsely-linked graph from drifting apart.
Automatically fit the graph to the viewport after a cluster is expanded or collapsed.
Remarks
These may be scalled based on the amount of node and canvas size