d3.js interpolation options

• linear - piecewise linear segments, as in a polyline.
• linear-closed - close the linear segments to form a polygon.
• step-before - alternate between vertical and horizontal segments, as in a step function.
• step-after - alternate between horizontal and vertical segments, as in a step function.
• basis - a B-spline, with control point duplication on the ends.
• basis-open - an open B-spline; may not intersect the start or end.
• basis-closed - a closed B-spline, as in a loop.
• bundle - equivalent to basis, except the tension parameter is used to straighten the spline.
• cardinal - a Cardinal spline, with control point duplication on the ends.
• cardinal-open - an open Cardinal spline; may not intersect the start or end, but will intersect other control points.
• cardinal-closed - a closed Cardinal spline, as in a loop.
• monotone - cubic interpolation that preserves monotonicity in y.

From: https://github.com/mbostock/d3/wiki/SVG-Shapes#wiki-line_interpolate