Pgfplots closes paths in polar plot

Question

I'd like to create an antenna radiation pattern in the form of a polar plot like this one: (image credits: C.A. Balanis; Antenna theory, analysis and design)

What I've done so far is the following code (the data file to make the example work is here):

\documentclass{standalone}

\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
        data cs=polar,
%       restrict x to domain=0:180,
%       restrict y to domain=0:180,
        ymin=-90,
        ymax=90,
        zmax=10.8,
        ]
\addplot3[surf,fill=white] table[x index={1},y index={0},z index={2}]{subarray-3d-plot-dir.csv};
\end{axis}
\end{tikzpicture}
\end{document}

but, strangely, pgfplots closes the paths between the first and the last point, as can be seen by the resulting image:

My questions:

• how to remove the segments that close the paths?
• how to improve the mesh/surface?

Clarification: the data file comes from a simulation software, so I don't have any means to change the way data are written in it.

Answer 1

Two things: You need to tell PGFPlots how many rows are in each block of data by setting mesh/rows=37 (alternatively, you could insert an empty row after each block of data, but since your file is generated by an external program, that's probably not an option here). Also, you need to set mesh/ordering=y varies, since by default, PGFPlots assumes that the x coordinate varies.

\documentclass[border=5mm]{standalone}

\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
        data cs=polar,
        ymin=-180, ymax=180,
        xmin=-180, xmax=180,
        zmin=-20, zmax=11,
        unit vector ratio*=1 1 10,
        z buffer=sort,
        view={45}{30},
        width=15cm
        ]
\addplot3[surf, fill=white, mesh/ordering=y varies, mesh/rows=37] table[x index={1},y index={0},z index={2}]{data.dat};
\end{axis}
\end{tikzpicture}
\end{document}