Batman Equation in LaTeX

Based on the answer from Gonzalo Medina, the Batman Equation in LaTeX is nearly finished.

\documentclass[border=10pt, tikz]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{arrows}

\tikzset{
>=stealth',
punkt/.style={
rectangle,
rounded corners,
draw=black, very thick,
text width=6.5em,
minimum height=2em,
text centered},
pil/.style={
->,
thick,
shorten <=2pt,
shorten >=2pt,}
}

\pgfplotsset{
grid style={gray, dashed, very thin},
every inner x axis line/.append style={pil},
every inner y axis line/.append style={pil},
}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
axis lines=middle,
grid=major,
xmin=-9,
xmax=9,
ymin=-9,
ymax=9,
xtick={-8,-7,...,8},
ytick={-8,-7,...,8},
width=12cm,
height=12cm,
]
set contour base;
set cntrparam levels discrete 0.0;
unset surface;
set view map;
set isosamples 500;
splot ((x/7.0)^2.0*sqrt(abs(abs(x)-3.0)/(abs(x)-3.0))+(y/3.0)^2.0*sqrt(abs(y+3.0/7.0*sqrt(33.0))/(y+3.0/7.0*sqrt(33.0)))-1.0);
splot (abs(x/2)-((3*sqrt(33)-7)/112)*x^2-3+sqrt(1-(abs(abs(x)-2)-1)^2)-y);
splot (9*sqrt(abs((abs(x)-1)*(abs(x)-.75))/((1-abs(x))*(abs(x)-.75)))-8*abs(x)-y);
splot (3*abs(x)+.75*sqrt(abs((abs(x)-.75)*(abs(x)-.5))/((.75-abs(x))*(abs(x)-.5)))-y);
splot (2.25*sqrt(abs((x-.5)*(x+.5))/((.5-x)*(.5+x)))-y);
splot (6*sqrt(10)/7+(1.5-.5*abs(x))*sqrt(abs(abs(x)-1)/(abs(x)-1))-(6*sqrt(10)/14)*sqrt(4-(abs(x)-1)^2)-y);
};
\end{axis}
\end{tikzpicture}

\end{document}


Questions and Trouble

The curves are seperated (they should be connected) and the curve is a little bit "bumby". So the functions should be connected and the bumps removed.

Furthermore I would like to fill the batman with an orange colour [orange!30], like it's shown on this plot.

Hopefully you can help ;-) ... kind regards! And thank you very much in advance!

Here is a pure TikZ/PGF/PGFPlots solution. You can declare a piecewise function with \pgfmathdeclarefunction to assure line joint. Your mathematical formula wasn't useful for me, instead I've used this formula.

Code

\documentclass[border=10pt]{standalone}
\usepackage{pgfplots}
\usetikzlibrary{arrows}
\usepgfplotslibrary{fillbetween}

% Below function
\pgfmathdeclarefunction{bA}{1}{\pgfmathparse{-3 * sqrt(1 - (#1/7)^2) * sqrt(abs(abs(#1) - 4)/(abs(#1) - 4))}}

\pgfmathdeclarefunction{bB}{1}{\pgfmathparse{abs(#1/2) - 0.0913722 * #1^2 - 3 + sqrt(1 - (abs(abs(#1) - 2) - 1)^2)}}

\pgfmathdeclarefunction{bpart}{1}{\pgfmathparse{%
(and(#1 >= -7, #1 < -4.03) * bA(#1))+%
(and(#1 >= -4.03, #1 <= 4.03) * bB(#1))+%
(and(#1 > 4.03, #1 <= 7) * bA(#1))}}

% Top Function
\pgfmathdeclarefunction{tA}{1}{\pgfmathparse{2 * sqrt((-abs(abs(#1) - 1)) * abs(3 - abs(#1))/((abs(#1) - 1) * (3 - abs(#1)))) * (1 + abs(abs(#1) - 3)/(abs(#1) - 3)) * sqrt(1 - (#1/7)^2) + (5 + 0.97 * (abs(#1 - 0.5) + abs(#1 + 0.5)) - 3 * (abs(#1 - 0.75) + abs(#1 + 0.75))) * (1 + abs(1 - abs(#1))/(1 - abs(#1)))}}

\pgfmathdeclarefunction{tB}{1}{\pgfmathparse{(2.71052 + 1.5 - 0.5 * abs(#1) - 1.35526 * sqrt(4 - (abs(#1) - 1)^2)) * sqrt(abs(abs(#1) - 1)/(abs(#1) - 1)) + 0.9}}

\pgfmathdeclarefunction{tpart}{1}{\pgfmathparse{%
(and(#1 >= -7, #1 <-3)* tA(#1))+%
(and(#1 >= -3, #1 <-1)* tB(#1))+%
(and(#1 >= -1, #1 <=1)* tA(#1))+%
(and(#1 > 1, #1 <=3)* tB(#1))+%
(and(#1 > 3, #1 <=7)* tA(#1))}}

\tikzset{
>=stealth',
punkt/.style={
rectangle,
rounded corners,
draw=black, very thick,
text width=6.5em,
minimum height=2em,
text centered},
pil/.style={
->,
thick,
shorten <=2pt,
shorten >=2pt,}
}

\pgfplotsset{
grid style={gray, dashed, very thin},
every inner x axis line/.append style={pil},
every inner y axis line/.append style={pil},
}

\begin{document}
\tikzset{batman/.style={domain=-7:7, very thick}}
\begin{tikzpicture}
\begin{axis}[
axis lines=middle,
grid=major,
xmin=-9,
xmax=9,
ymin=-9,
ymax=9,
xtick={-8,-7,...,8},
ytick={-8,-7,...,8},
width=12cm,
height=12cm,
]