Thread Subject: Log axis on surf plot

I noticed that the plot output in specgram (now obsolete and
called spectrogram) has been changed from 'image(...)' to
'surf(...)'

This is a welcome improvement.

But now I would like to use a log axis for the frequency
axis since my signal covers many decades in frequency
content. I realize the I can just form 'log10(f)' and plot
it as a linear axis but this is difficult to interpret when
analyzing the plot (e.g. what is the freq if log10(f)=0.4 ?)

Is there anyway to get a genuine log axis (1, 10 100, 1000)
in surf?

"Paul " <par@ceri.memphis.edu> wrote in message
news:g92vi9$s6k$1@fred.mathworks.com...
>I noticed that the plot output in specgram (now obsolete and
> called spectrogram) has been changed from 'image(...)' to
> 'surf(...)'
>
> This is a welcome improvement.
>
> But now I would like to use a log axis for the frequency
> axis since my signal covers many decades in frequency
> content. I realize the I can just form 'log10(f)' and plot
> it as a linear axis but this is difficult to interpret when
> analyzing the plot (e.g. what is the freq if log10(f)=0.4 ?)
>
> Is there anyway to get a genuine log axis (1, 10 100, 1000)
> in surf?


[x,y,z] = peaks;
mz = min(z(:));
% I shift the z values in the SURF call below so that all the z coordinates
are positive
% that way, when I change the Z axis to be in log scale, all of the points
have a real logarithm
% and so can be shown on the plot.
surf(x, y, z-mz+1);
set(gca, 'ZScale', 'log')


You may also want to SET the ZTick and/or ZTickLabel properties to customize
the appearance of the axes. Look here for a list of properties of the axes
that you can SET:

http://www.mathworks.com/access/helpdesk/help/techdoc/infotool/hgprop/axes_frame.html

--
Steve Lord
slord@mathworks.com

On Aug 27, 3:26=A0am, "Paul " <p...@ceri.memphis.edu> wrote:
> I noticed that the plot output in specgram (now obsolete and
> called spectrogram) has been changed from 'image(...)' to
> 'surf(...)'
>
> This is a welcome improvement.
>
> But now I would like to use a log axis for the frequency
> axis since my signal covers many decades in frequency
> content. =A0I realize the I can just form 'log10(f)' and plot
> it as a linear axis but this is difficult to interpret when
> analyzing the plot (e.g. what is the freq if log10(f)=3D0.4 ?)
>
> Is there anyway to get a genuine log axis (1, 10 100, 1000)
> in surf? =A0

I've been using surf(log10(f)), turning off the tick marks and labels
for the frequency axis, then creating another axis over that with the
appropriate log scale.
It's a serious pain and is probably not the best way to do it, but it
works.

Paul wrote:

> Is there anyway to get a genuine log axis (1, 10 100, 1000)
> in surf?

Set the axis XScale or YScale or ZScale property to be 'log'.
There are the usual issues about what happens to true 0's
(the points get dropped from the plot) but I don't see any
difficulty otherwise.

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