Draw vertical lines on matlab spectrogram plot

Question

Does the matlab spectrogram function lock the created figure in anyway? I want to draw vertical lines on the figure but the line function does not seem to do anything. How can I draw a line on a matlab spectrogram?

clc; clear all; close all;
[data, fs, nbits] = wavread(<INSERT WAVE FILE HERE>);
% [data, fs, nbits] = wavread('white_0.05_6sec_aud.wav');


N_data=length(data); N_frame=128; N_half=N_frame/2; N_loop=N_data/(N_half);
output=zeros(N_data,1);
hz=0:(fs/2)/N_half:(fs/2)-(fs/2)/N_half;

spectrogram(data, hanning(N_frame), N_half, N_frame, fs);

x = [6500 6500];
y = [0 5.5];

H = gca;

% set(gca, 'NextPlot', 'add');
% line(x, y);

h = line([6500, 6500], [0, 5.5]);
set(h, 'parent', handles.predicted_ax);

% view(-90,90)
% set(gca,'ydir','reverse')
% 
% [y, x] = ginput(1)


% view(-90, 180);

Answer 1

The spectogram generates a surf and sets the view to (0,90). The surf sets the zlim to some values (dependent on the spectrogram data), and apparently, adding a line to the current plot does not change the zlim (probably because spectrogram locked the axes somehow; should be findable in edit spectrogram). Therefore, in view(0,90), the line completely disappears (rotate the plot; you'll see the line appear somewhere above the surface).

To resolve: the way you add a line defaults to the line having z-coordinates of [0 0], which, for many spectrograms, will be above the range of the axes set by spectrogram.

Issuing

zl = zlim;
axis([xlim ylim zl(1) max(0, zl(2))])
view(0,90)

after the line should then make the line appear.

Also: in my case, the surface over which the line was hovering was mostly blue, as was the line. This doesn't help making it apparent there is a line :) I made it white, which contrasted better with the blue/yellow/red surf below.