Editing Trigonometric integral (section)

== Nielsen's spiral ==
[[Image:Nielsen's spiral.png|thumb|Nielsen's spiral.]]
The [[spiral]] formed by parametric plot of {{math|si, ci}} is known as Nielsen's spiral.
<math display="block">x(t) = a \times \operatorname{ci}(t)</math>
<math display="block">y(t) = a \times \operatorname{si}(t)</math>

The spiral is closely related to the [[Fresnel integral]]s and the [[Euler spiral]]. Nielsen's spiral has applications in vision processing, road and track construction and other areas.<ref>{{cite book|last=Gray|title=Modern Differential Geometry of Curves and Surfaces.|publisher=|year=1993|isbn=|location=Boca Raton|pages=119}}</ref>