TikZ：foreach 循环中的行问题

Question

\documentclass[tikz]{standalone}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
  \coordinate (h) at (0, 3);
  \coordinate (O) at (0, 0);

  \draw (O) -- +(-3, 0);
  \draw[-latex] (O) -- +(3, 0) node[right, font = \scriptsize] {$x$};
  \draw[-latex] (O) -- +(0, 4) node[above, font = \scriptsize] {$z$};

  \foreach \x/\s in {-1.5/{-}, 1.5/{+}}{
    \draw (\x, 0) -- +(0, -0.1) node[below, font = \scriptsize] (l\s) at
    (\x, 0) {$\s\frac{\ell}{2}$};
  }

  \draw (l-.center) -- (h);
  \draw (l+.center) -- (h);
\end{tikzpicture}
\end{document}

我的最后两条线是根据标签绘制的，而不是我预期的 x 截距线。这怎么可能正确呢？

Answer 1

您可以coordinate在路径内使用来命名精确的坐标。您正在命名节点以下所需的坐标。

代码

\documentclass[tikz]{standalone}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
  \coordinate (h) at (0, 3);
  \coordinate (O) at (0, 0);

  \draw (O) -- +(-3, 0);
  \draw[-latex] (O) -- +(3, 0) node[right, font = \scriptsize] {$x$};
  \draw[-latex] (O) -- +(0, 4) node[above, font = \scriptsize] {$z$};

  \foreach \x/\s in {-1.5/{-}, 1.5/{+}}{
    \draw (\x, 0) coordinate (l\s) -- +(0, -0.1) node[below, font = \scriptsize] at
    (\x, 0) {$\s\frac{\ell}{2}$};
  }

  \draw (l-.center) -- (h);
  \draw (l+.center) -- (h);
\end{tikzpicture}
\end{document}

输出