7

I want to draw the tangent line as well as the normal line for an arbitrary curve as follows.

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pstricks-add}

\begin{document}
\begin{pspicture}[showgrid](6,3)
    \pscurve[curvature=1 1 1](0,0)(1,2)(2,1)(4,2)(6,1)
    \psTangentLine[Tnormal,linecolor=blue](2,1)(4,2)(6,1){3}{0.25}
    \psTangentLine[linecolor=red](2,1)(4,2)(6,1){3}{1}
    \pscircle*[linecolor=green](OCurve){3pt}
\end{pspicture}
\end{document}

enter image description here

Unfortunately, the point through which the above lines pass is not on the curve. What is wrong? And how to solve it?

kiss my armpit
  • 36,086

1 Answers1

7

The problem comes from the fact that you are drawing your tangent on another curve than the original one. The first is defined with 5 points and is not the one defined with 3.

enter image description here

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pstricks-add}

\begin{document}
\begin{pspicture}[showgrid](6,3)
    \pscurve[curvature=1 1 1,linecolor=yellow](0,0)(1,2)(2,1)(4,2)(6,1)
    \pscurve[curvature=1 1 1](2,1)(4,2)(6,1)
    \psTangentLine[Tnormal,linecolor=blue](2,1)(4,2)(6,1){3}{0.25}
    \psTangentLine[linecolor=red](2,1)(4,2)(6,1){3}{1}
    \pscircle*[linecolor=green](OCurve){3pt}
\end{pspicture}
\end{document}
Tarass
  • 16,912
  • While your observation is correct, it doesn't show how to draw the correct tangents. – Christoph May 27 '14 at 17:17
  • Sorry but don't use pstricks for 4 years, and I don't know all this knew commands. I just tried somehing that came out in my memory. Could \psTangentLine syntax support 5 points difined curve ? If yes you have the solution, otherwise ... – Tarass May 27 '14 at 17:28
  • As one can see on page 41 in the pstricks add manual, http://math.sut.ac.th/lab/software/texlive/texmf-dist/doc/generic/pstricks-add/pstricks-add-doc.pdf, one has to immitate the curve with 3 points, otherwise one has to give the mathematical equation of the curve. – Tarass May 28 '14 at 07:22