Change data sign in pgfplots

Question

I'm dealing with a 3d plot. Let's consider the following MWE:

\documentclass{article}

\usepackage{pgf,pgfplots,pgfplotstable}
\pgfplotsset{compat=newest}
\usepgfplotslibrary{colormaps}
\usepgfplotslibrary{groupplots}
\usetikzlibrary{arrows.meta}

\begin{filecontents*}{data.dat}
       rx         ry       rz
-24.86780    0.00000    1.000
-24.41886    0.00002    1.000
-23.97329    0.00010    0.999
-23.53110    0.00022    0.998
-23.09230    0.00039    0.996
-22.65693    0.00061    0.994
-22.22498    0.00087    0.991
-21.79648    0.00118    0.988
-21.37144    0.00153    0.985
-20.94988    0.00192    0.981
-20.53182    0.00236    0.976
-20.11727    0.00285    0.972
\end{filecontents*}

\begin{document}

\begin{figure}[htbp]
    \centering
 
    \begin{tikzpicture}
    \begin{axis}[
        title = Trajectory,
        xmin = -25, xmax = -19,
        ymin = -1, ymax = 1,
        zmin=0.8, zmax=1,
        xtick distance = 5,
        ytick distance = 1,
        xlabel={$downrange$},
        ylabel={$crossrange$},
        zlabel={$altitude$},
        y label style={sloped},
        x label style={sloped},
        grid = both,
        grid style = {dotted},
        minor tick num = 1,
        major grid style = {lightgray!75},
        minor grid style = {lightgray!75},
        width = 0.85\textwidth,
        height = 0.50\textwidth,
        view={65}{40},
        %scale only axis,
        legend cell align = {left},
        legend pos = north east
    ]


    \addplot3 [smooth, black, ultra thick] table [x = {rx}, y = {ry}, z = {rz}] {data.dat};
    \addplot3 [smooth, black, loosely dashed, ultra thick] table [x = {rx}, y = -{ry}, z = {rz}] {data.dat};

    \legend{
    n1 (k),
    n1 (j),
}
 
\end{axis}
\end{tikzpicture}
\caption{plot}
\end{figure}



\end{document}

I would like to know how I could add a new plot, in addition to the one I've written, where the sign of every y is inverted. I've tried both y={-ry} and y=-{ry} inside a new addplot, but it doesn't work. I suppose that in the first case the algorithm doesn't find any column named "-ry", that's why it reports the error, while I have no idea for the latter case.

Is there any strategy to change the sign of the values of a single column without creating a completely new data table?

Answer 1

You're after

y expr= -\thisrow{ry}

rather than y=-ry. In y expr (and similarly x expr, z expr) you provide an expression where you access the data in the file with \thisrow{<column name>}.