Problem with quiver plot function

Question

Penny 2018-9-21

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/420190-problem-with-quiver-plot-function

评论： Adam 2018-9-24

I am working on some code which I have been trying to tidy up into functions as I have several versions of it and it's quite repetitive. One of the tasks is a quiver plot, which I have written this function (Qplot) for:

function  Qplot( space, lat, lon, u, v, size, thick )
%UNTITLED6 Summary of this function goes here
%   Detailed explanation goes here
hold on
r = 1:str2double(space):length(lat);
r1 = lat(r);
s = 1:str2double(space):length(lon);
s1 = lon(s);
us = u(r, s);
vs = v(r, s);
q = quiver(s1,r1,us,vs);
q.AutoScaleFactor = str2double(size);
q.LineWidth = str2double(thick);
q.Color = 'k';
hold off
end

This works fine on most versions of the code except one. I have had to take out the Qplot bit out (it's there commented out) and replace it with the content of the function in full, like this:

function pushbutton23_Callback(hObject, eventdata, handles) %#ok<*INUSL>
    h = guidata(gcbo);
    axes(handles.axes2)
    % Qplot(handles.edit22.String, h.latf, h.lonf, h.uf. h.vf, handles.edit21.String, handles.edit23.String)
  hold on
r = 1:str2double(handles.edit22.String):length(h.latf);
r1 = h.latf(r);
s = 1:str2double(handles.edit22.String):length(h.lonf);
s1 = h.lonf(s);
us = h.uf(r, s);
vs = h.vf(r, s);
q = quiver(s1,r1,us,vs);
q.AutoScaleFactor = str2double(handles.edit21.String);
q.LineWidth = str2double(handles.edit23.String);
q.Color = 'k';
hold off

If I use the Qplot function in that one version only, I get this error message, but in no others where I'm doing exactly the same thing:

Struct contents reference from a non-struct array object.
Error in guiglobal>pushbutton23_Callback (line 280)
Qplot(handles.edit22.String, h.latf, h.lonf, h.uf. h.vf, handles.edit21.String, handles.edit23.String)
Error in gui_mainfcn (line 95)
        feval(varargin{:});
Error in guiglobal (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)guiglobal('pushbutton23_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating UIControl Callback

Any ideas?

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Penny 2018-9-24

在 MATLAB Online 中打开

Name           Size                Bytes  Class                             Attributes
eventdata      1x1                   112  matlab.ui.eventdata.ActionData              
h              1x1             468330720  struct                                      
hObject        1x1                   112  matlab.ui.control.UIControl                 
handles        1x1             468330720  struct

ans =

    'figure1'
    'pushbutton52'
    'uipanel12'
    'uipanel6'
    'uipanel8'
    'uipanel5'
    'uipanel4'
    'uipanel2'
    'uipanel1'
    'text1'
    'text28'
    'text27'
    'axes2'
    'axes1'
    'text86'
    'text85'
    'edit28'
    'edit27'
    'pushbutton50'
    'pushbutton49'
    'pushbutton21'
    'edit6'
    'edit3'
    'edit5'
    'edit2'
    'text34'
    'text33'
    'text25'
    'text24'
    'edit23'
    'text55'
    'edit22'
    'text54'
    'pushbutton23'
    'edit21'
    'text53'
    'text39'
    'text38'
    'text36'
    'text35'
    'text32'
    'text31'
    'text22'
    'text21'
    'pushbutton19'
    'edit1'
    'pushbutton20'
    'text2'
    'pushbutton43'
    'text79'
    'pushbutton25'
    'text57'
    'pushbutton12'
    'pushbutton11'
    'pushbutton8'
    'pushbutton7'
    'text14'
    'text13'
    'text10'
    'text9'
    'pushbutton42'
    'text78'
    'pushbutton24'
    'text56'
    'pushbutton6'
    'pushbutton5'
    'pushbutton2'
    'pushbutton1'
    'text8'
    'text7'
    'text4'
    'text3'
    'output'
    'ufa'
    'imAlpha'
    'vfa'
    'data'
    'uf'
    'vf'
    'lonf'
    'latf'
    'flon'
    'flat'
    'imAlpha2'

ans =

    'figure1'
    'pushbutton52'
    'uipanel12'
    'uipanel6'
    'uipanel8'
    'uipanel5'
    'uipanel4'
    'uipanel2'
    'uipanel1'
    'text1'
    'text28'
    'text27'
    'axes2'
    'axes1'
    'text86'
    'text85'
    'edit28'
    'edit27'
    'pushbutton50'
    'pushbutton49'
    'pushbutton21'
    'edit6'
    'edit3'
    'edit5'
    'edit2'
    'text34'
    'text33'
    'text25'
    'text24'
    'edit23'
    'text55'
    'edit22'
    'text54'
    'pushbutton23'
    'edit21'
    'text53'
    'text39'
    'text38'
    'text36'
    'text35'
    'text32'
    'text31'
    'text22'
    'text21'
    'pushbutton19'
    'edit1'
    'pushbutton20'
    'text2'
    'pushbutton43'
    'text79'
    'pushbutton25'
    'text57'
    'pushbutton12'
    'pushbutton11'
    'pushbutton8'
    'pushbutton7'
    'text14'
    'text13'
    'text10'
    'text9'
    'pushbutton42'
    'text78'
    'pushbutton24'
    'text56'
    'pushbutton6'
    'pushbutton5'
    'pushbutton2'
    'pushbutton1'
    'text8'
    'text7'
    'text4'
    'text3'
    'output'
    'ufa'
    'imAlpha'
    'vfa'
    'data'
    'uf'
    'vf'
    'lonf'
    'latf'
    'flon'
    'flat'
    'imAlpha2'

Adam 2018-9-24

在 MATLAB Online 中打开

I can't see any logical reason why calling a function in that case would yield that error while using the exact same variables and fields in place does not.

There are some oddities about the code that make it more likely for bugs to creep in, but these should not cause what you are seeing, e.g.

h = guidata(gcbo);

is totally un-necessary. This is exactly what 'handles' is at this point in the code.

axes(handles.axes2)
% Qplot(handles.edit22.String, h.latf, h.lonf, h.uf. h.vf, handles.edit21.String, handles.edit23.String)
hold on

You should get used to always passing axes handles to plotting instructions such as hold rather than relying on the fact the changing the active axes and then plotting or calling hold will always work exactly as expected.

Passing the axes handle to Qplot and then calling

quiver( hAxes,... )

and

hold( hAxes, 'on' )

is more robust.

I don't see why either of these issues should cause the code not to work in this case though.

You should be able to see the problem with a breakpoint though when you get the error. Look at each of the arguments to the Qplot function in turn on the command line and one of them should throw the error you get. Again though I see no logical reason why this would be the case while calling Qplot, but not when using the pasted code.

Penny 2018-9-24

Handles only covers the axes, that line is needed because I also need to access variables in the h. structure to tell it what to plot.

What might it not do as expected? Turns out that's not the problem here, there was a typo as spotted below, but I am interested in what that does which my current code does not. It seems to robustly always plot to the correct axes regardless of what else I've been doing.

Adam 2018-9-24

在 MATLAB Online 中打开

h = guidata(gcbo);

gives you the handles struct. The exact same one that you get passed into the function as 'handles'.

Generally code using

axes( obj.hAxes )

followed by a load of plot related instructions will work fine, but from time to time you will find a case where the 'current axes' changed without you realising between you calling axes and actually plotting data. I have had numerous occasions when I forgot to give explicit axes handles when I suddenly get an axes appearing in a figure I wasn't expecting it.

So sure, it may work in all cases you have had so far, but it is just good practice to give explicit handles to plot instructions rather than just hope that nothing unexpectedly changes the current axes before you plot (e.g. a user clicking on a different axes will change the current axes too).

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Answer 1

Dennis 2018-9-24

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/420190-problem-with-quiver-plot-function#answer_338164

在 MATLAB Online 中打开

You got a typo:

Qplot(handles.edit22.String, h.latf, h.lonf, h.uf. h.vf, handles.edit21.String, handles.edit23.String)
                                                 ^^ this should be a ,

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