function getOrSet (obj, key, func) {
  let result = obj[key];
  if (result === undefined) {
    result = func();
    obj[key] = result;
  }
  return result;
}
NOTE: The getOrSet function plus the "const xyzGeometries" constants below
allowes the sharing/reuse of THREE geometries between nodes.  The "key"
identifies the radius and/or outer radius+inner radius of the geometry the
node is going to use and if it already exist it isn't duplicated but will
"reuse" the existing geometry of the same configuration.
  FYI: materials aren't shared to allow per node color.
aSqrd-eSqrd, 20-May-2019