function modifyRow(row) {
  const {radius, angle, angle0} = row;
  const truedAngle = -1 * angle + Math.PI / 2;
  const truedAngle0 = -1 * angle0 + Math.PI / 2;
  return {
    ...row,
    x: radius * Math.cos(truedAngle),
    y: radius * Math.sin(truedAngle),
    angle: truedAngle,
    angle0: truedAngle0
  };
}
Prepare the internal representation of row for real use.
This is necessary because d3 insists on starting at 12 oclock and moving
clockwise, rather than starting at 3 oclock and moving counter clockwise
as one might expect from polar
@param {Object} row - coordinate object to be modifed
@return {Object} angle corrected object