in src/services/dataRenderService.ts [291:310]
private drawOuter(element: Selection<any>) {
let outlineArc: any = arc()
.innerRadius(this.settings.outerLine.showStraightLines ? this.innerRadius : this.outerRadius)
.outerRadius(this.outerRadius);
let outerThickness: string = this.settings.outerLine.thickness + "px",
color: string = this.settings.outerLine.color;
let outerLine = element.selectAll(DataRenderService.OuterLine.selectorName).data(this.dataPoints);
outerLine.exit().remove();
outerLine = outerLine.merge(outerLine.enter().append("path"));
outerLine
.attr("fill", "none")
.attr("opacity", 0.5)
.attr("stroke", color)
.attr("stroke-width", outerThickness)
.attr("d", <ArcDescriptor<any>>outlineArc)
.classed(DataRenderService.OuterLine.className, true);
}