ほとんど連投になってしまい申し訳ないのですが，Tikzについてです． 3次元極座標をかこうとしています（図参照．）．しかし，余計に弦が現れます．コードは以下の通りです． \begin{tikzpicture} \begin{axis}[% axis equal, view={110}{25}, width=10cm, height=10cm, axis lines = center, xlabel = {$x$}, ylabel = {$y$}, zlabel = {$z$}, ticks=none, enlargelimits=0.3, scale uniformly strategy=units only ] \addplot3[% opacity = 0.5, surf, shader=interp, fill=lightgray, draw=none, z buffer = sort, samples = 30, variable = \u, variable y = \v, domain = 0:180, y domain = 0:360, ] ({cos(u)*sin(v)}, {sin(u)*sin(v)}, {cos(v)}); \addplot3[mark=none, color=black, line width=0.5pt, variable y=\v, y domain=0:90, samples=20, smooth] ({cos(60)*sin(v)},{sin(60)*sin(v)},{cos(v)}); \addplot3[mark=none, color=black, line width=0.5pt, variable=\u, domain=0:360, samples=50, smooth] ({cos(u)},{sin(u)},{0}); \addplot3[only marks,mark=*,mark size=0.8pt] coordinates {({cos(60)*sin(45)},{sin(60)*sin(45)},{cos(45)})}; \addplot3[ ->,>=stealth, postaction={ decorate, decoration={ markings, mark=at position 1 with {\arrow[scale=0.8]{>}} } } ] coordinates {(0,0,0) ({cos(60)*sin(45)},{sin(60)*sin(45)},{cos(45)})}; \addplot3[dashed] coordinates {({0},{0},{cos(45)})({cos(60)*sin(45)},{sin(60)*sin(45)},{cos(45)}) ({cos(60)*sin(45)},{sin(60)*sin(45)},{0}) (0,0,0)}; \addplot3 [variable y=\v,y domain=0:45,samples=30,smooth] ({0.5*cos(60)*sin(v)},{0.5*sin(60)*sin(v)},{0.5*cos(v)}); ¥node[left] at(0,0,0.5) {$\varphi$}; \addplot3[variable=\u,domain=0:60,samples=40,smooth] ({0.5*cos(\u)},{0.5*sin(\u)},{0}); \end{axis} \end{tikzpicture}
