How to extract only the data points from BodePlot plot?

I am trying to fix the Phase plot part of BodePlot, as it does not wrap correctly. And there is no option that I can use to tell it to wrap.

So, instead of doing the full plo开发者_Python百科t myself, (I can do that if I have to) I am thinking of first making the BodePlot, grab the data points, do the wrapping on the data (once I get the x,y data, the rest is easy), then I need to put the new list of points back into the plot, and then use Show to display it.

The part I am stuck at, is extracting the points from FullForm. I can't get the correct Pattern to do that.

This is what I go to so far:

hz=z/(z^2-z+0.3);
tf=TransferFunctionModel[hz,z,SamplingPeriod->2];
phasePlot=BodePlot[tf,{0.001,2 Pi},
       ScalingFunctions->{Automatic,{"Linear","Degree"}},PlotLayout->"List"][[2]]

You see how it does not wrap at 180 degrees. It is more common in dsp that Bode phase plot wraps. Here is what it 'should' look like:

So, this is what I did:

 FullForm[phasePlot]
Graphics[List[
  List[List[], List[], 
   List[Hue[0.67, 0.6, 0.6], 
    Line[List[List[0.0010000243495554542, -0.2673870119911639], 
      List[0.0013659538057574799, -0.36521403872250247], 
      List[0.0017318832619595053, -0.46304207336414027],
      ....

I see the data there (the x,y) But how to pull them out? I tried this:

  Cases[FullForm[phasePlot], List[x_, y_] -> {x, y}, Infinity];

But the above matches in addition to the list of point, other stuff that I do not need. I tried many other things, but can't get only the list of points out.

I was wondering if someone knows how to pull only the (x,y) points from the above plot. Is there a better way to do this other than using FullForm?

Thanks

Update:

I just find a post here which shows how to extract data from plot. So I used it:

   points = Cases[Normal@phasePlot, Line[pts_] -> pts, Infinity]

You could do try nesting the replacement rules, for example

phase2 = phasePlot /. 
    Line[a_] :> (Line[a] /. {x_?NumericQ, y_?NumericQ} :> {x, Mod[y, 360, -180]});
Show[phase2, PlotRange -> {Automatic, {-180, 180}}, FrameTicks -> Automatic]

Output:

The list you are looking for appears to be wrapped by Line[], and it seems to be the only case in your plot. So you could use

Cases[phasePlot, Line[list_] :>  list, Infinity]

Edit: When I posted my response, the page refreshed and I saw that you came across precisely what I had proposed. I'll leave my response posted here anyway.

Edit2: Szabolics pointed out that FullForm[] has no effect, so I removed it from my original posting.