使用 tikz 角度时的间隙

Question

当我尝试使用以下代码绘制角度 alpha 和 theta 时，我在角度上得到了一些奇怪的间隙或悬垂。这是我第一次使用 tikz 绘制角度，所以我不知道我是否做错了什么。谢谢您的帮助！

\begin{figure}
    \centering
    \begin{tikzpicture}
        \coordinate (test2) at (0,0);
        \draw[->, thick] (0,0) -- (4,0) node[right] (test1) {x};
        \draw[->, thick] (0,0) -- (0,4) node[above] {y};
        \draw[->] (0, 0) -- (2, 2) node[below] (test3) {r};
        \draw pic[pic text = {$\theta$}, draw, -, angle eccentricity=1.3, angle radius = 15] {angle = test1--test2--test3};
        \draw[dashed] (2, 2) -- (2, {2 + 1.25}) node[] (dashed) {};
        \draw (2, 2) -- ({2+1}, {2 + 0.5}) node[] (bold) {};
        \draw pic[pic text = {$\alpha$}, draw, -, angle eccentricity=1.2, angle radius = 30] {angle = bold--test3--dashed};

        \draw[dashed] ({sqrt(8)}, 0) arc[start angle = 0, end angle = 90, radius ={sqrt(8)}];
    \end{tikzpicture}
    \caption{Caption}
    \label{fig:halbachwinkel}
\end{figure}   

Answer 1

角度处的间隙是由于使用节点名称作为定义角度的坐标造成的。如果您将这些节点替换为\coordinate，则一切都会正常工作：

\documentclass[12pt, margin=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{angles, arrows.meta,    % new
                quotes}                 % new

\begin{document}
    \begin{tikzpicture}[
ang/.style = {draw, Straight Barb-Straight Barb, anchor=west,
              angle radius = 8mm, angle eccentricity=1},
arr/.style = {cap=round,-Straight Barb},
                        ]
\coordinate (test2) at (0,0);
% axix
\draw[arr] (0,0) -- (4,0) node[right] (test1) {x};
\draw[arr] (0,0) -- (0,4) node[above] {y};
% vector
\draw[arr, thick] (test2) -- (2, 2) 
    coordinate[label={[inner sep=1ex]270:r}] (test3);
% angle theta  
\pic[ang, "$\theta$"] {angle = test1--test2--test3};
% circle
\draw[densely dashed] ({sqrt(8)},0) arc (0:90:{sqrt(8)});
% angle alpha
\draw[dashed]   (test3) -- ++ (0,1.25) coordinate (dashed) {};
\draw           (test3) -- ++ (+1,0.5) coordinate (bold) {};
\pic[ang, "$\alpha$"] {angle = bold--test3--dashed};
    \end{tikzpicture}
\end{document}