Problem in increasing the distance between labels in contour plot in a TikZ picture

I am having problem in increasing the distance between the labels in a contour plot in a TikZ picture. I tried a value from 10 to 10000 for the key contour/label distanc just to have only one label on each contour level. All I tried didn't give me the result I want. Is there something that I am missing?

Here is the code I used:

\documentclass[crop=true,border=0mm]{standalone}
\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
axis on top,
title = {$\omega_\phi\left(x, \sigma\right) = \frac{\Gamma}{\pi{R_c}^2}\exp\left[-\frac{\left(x-x_0\right)^2+\left(\sigma-R_0\right)^2}{{R_c}^2}\right]$},
xmin=2, xmax=3,
ymin=2, ymax=3,
view={0}{90},
xlabel = {$x$},
ylabel = {$\sigma$},
]
contour gnuplot = {contour label style={
nodes={text=black},
/pgf/number format/fixed,
/pgf/number format/fixed zerofill=true,
/pgf/number format/precision=1,}},
samples=2000,
contour/draw color={black},
contour/label distance=1000,
]
{1/3.1415927/0.25^2*exp(-((x-2.5)^2+(y-2.5)^2)/0.25^2)};
\end{axis}
\end{tikzpicture}

\end{document}


I couldn't get contour/label distance=1000, to work for my case. The following is the picture of the above code with samples=2000 and contour/label distance=1000,. I would like to have only one label on each contour.

Could someone help me?

-

contour/label distance is a length and needs some units, e.g. you should write 1000pt rather than just 1000. The default value is 70pt. Here are two cruder plots with different values for this parameter:

\documentclass[crop=true,border=0mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
axis on top,
xmin=-1, xmax=1,
ymin=-1, ymax=1,
view={0}{90},
xlabel = {$x$},
ylabel = {$\sigma$},
]
contour gnuplot = {contour label style={
nodes={text=black},
/pgf/number format/fixed,
/pgf/number format/fixed zerofill=true,
/pgf/number format/precision=1,}},
contour/draw color={black},
contour/label distance=1000pt,
]
{exp(-(x^2+y^2)};
\end{axis}
\end{tikzpicture}

\begin{tikzpicture}
\begin{axis}[
axis on top,
xmin=-1, xmax=1,
ymin=-1, ymax=1,
view={0}{90},
xlabel = {$x$},
ylabel = {$\sigma$},
]
contour gnuplot = {contour label style={
nodes={text=black},
/pgf/number format/fixed,
/pgf/number format/fixed zerofill=true,
/pgf/number format/precision=1,}},
contour/draw color={black},
contour/label distance=50pt,
]
{exp(-(x^2+y^2)};
\end{axis}
\end{tikzpicture}

\end{document}


Adding a samples option works, but only up to a certain threshhold. Here is the case with samples=100 which is as expected. If you change to samples=131 then the label spacing changes, perhaps due to some overflow problem.

samples=100

samples=131

% arara: pdflatex: { shell: yes }
\documentclass[crop=true,border=0mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
axis on top,
xmin=-1, xmax=1,
ymin=-1, ymax=1,
view={0}{90},
xlabel = {$x$},
ylabel = {$\sigma$}]
contour gnuplot = {contour label style={
nodes={text=black},
/pgf/number format/fixed,
/pgf/number format/fixed zerofill=true,
/pgf/number format/precision=1}},
contour/draw color={black},contour/label distance=1000pt]
{exp(-(x^2+y^2)};
\end{axis}
\end{tikzpicture}

\begin{tikzpicture}
\begin{axis}[
axis on top,
xmin=-1, xmax=1,
ymin=-1, ymax=1,
view={0}{90},
xlabel = {$x$},
ylabel = {$\sigma$}]
contour gnuplot = {contour label style={
nodes={text=black},
/pgf/number format/fixed,
/pgf/number format/fixed zerofill=true,
/pgf/number format/precision=1}},
contour/draw color={black},contour/label distance=50pt]
{exp(-(x^2+y^2)};
\end{axis}
\end{tikzpicture}

\end{document}

-
Thanks @Andrew. It works fine when the number of samples are low. There is one problem. Since I want to have a smooth contour line, I used samples=2000. Even using contour/label distance=10000pt does not produce the contour levels to have only one label. Could you please comment on the sample size? All my packages are updated to their latest version. –  A2009 Mar 5 '13 at 2:32
You are right, when the number of samples is high, the label distance option seems to not have the desired effect. In my example, samples=130 is fine, samples=131 causes the labels to be misplaced. My guess is that this some arthmetic overflow. Note that samples=100 gives a fairly smooth plot in my example. –  Andrew Swann Mar 5 '13 at 11:46
PS your example compiles without label problems for samples=250 and is reasonably smooth. Testing higher values is taking too much time on my machine. –  Andrew Swann Mar 5 '13 at 12:30