Drawing Unconnected 3D Arc in PGFPlots

Question

I am trying to draw a 3-dimensional half circle arc in PGFPlots using a parametric equation. This is the relevant code.

\documentclass{article}
\usepackage{tikz}
\usepackage{pgfplots}

\pgfplotsset{compat=1.17}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
    axis lines=middle,
    ticks=none,
    view = {135}{20},
    xlabel=$x$,
    ylabel=$y$,
    zlabel=$z$,
    xmin=-1, xmax=1,
    ymin=-1, ymax=1,
    zmin=0, zmax=1,
    unit vector ratio = 1 1 1,
]
\addplot3[domain=-0.25*pi:0.75*pi,red]
({0.5*cos(deg(x))},{0.5*sin(deg(x))},{0.5});
\end{axis}
\end{tikzpicture}

\end{document}

It doesn't look how I want it to, however. I do not want the ends of the arc to be connected. How do I fix this? Thanks in advance!

Answer 1

\documentclass[tikz, border=1cm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
axis lines=middle,
ticks=none,
view={135}{20},
xlabel=$x$,
ylabel=$y$,
zlabel=$z$,
xmin=-1, xmax=1,
ymin=-1, ymax=1,
zmin=0, zmax=1,
%unit vector ratio = 1 1 1,
axis equal,
scale mode=none,
trig format plots=rad,
]
\addplot3[domain=-0.25*pi:0.75*pi, red, samples y=1]({0.5*cos(x)},{0.5*sin(x)},{0.5});
\end{axis}
\end{tikzpicture}
\end{document}

From manual p. 125

If you use \addplot3 expression, mesh/rows and mesh/cols are computed from the values samples and samples y. By default, \addplot3 expression always samples a mesh. If you want it to sample a line, set samples y=1 (or, equivalently, y domain=0:0).