Problem using setAxisScaleDraw and QwtPlotZoomer

Hello,

I have to plot curves using QDateTime as x-axis. I'm using setAxisScaleDraw and using my return as below:

Code:

---

return QDateTime::fromTime_t( v ).toString( "hh:mm:ss" );

---

It's working fine and plotting everything right. I added a QwtPlotZoomer to my software to perform the zoom possibility, and it's working also fine.

The problem is: when I try to zoom a small part of the curve, for example, if I want to zoom some part that is less than one minute, my x-axis keeps with one minute size and my curve goes to the center of the screen, it doens't use the whole plot area.

Example:

The figure below, I have current and voltage plotted, and I zoomed just one part, represented using blue arrows.

Attachment 7975

The figure below is the result of the first zoom, showed at figure above:

Attachment 7976

It's possible to see that QwtPlotZoomer is working fine and also the scaleDraw. I zoomed a big part, then it works fine. The third figure (figure below) shows the result of the last zoom (figure above):

Attachment 7977

And then I zoomed again the last figure, just a small part. And I get my problem, my last zoom is just 3 seconds, but the x-axis keeps with almost one minute and my graph goes to the center of the plot area (figure below):

Attachment 7978

My question: is there a limit for the scaleDraw? I tried to use milliseconds, but I couldn't find a way to do that, I don't know exactly how it works. I would like to use always the whole plotting area, and don't have this small piece of curve. Someone has any ideia why it's happening that?

I hope someone can understand my problem and help me, if you have any questions I can try to explain again.

Qwt classes only know about doubles - the fact that those are somehow related to date/time values is completely in your code.

Uwe

Uwe, sorry, but I didn't understand what you meant.
Can you explain again?
Thanks

Quote:

---

Originally Posted by cesroc

Uwe, sorry, but I didn't understand what you meant.

---

Eliminate the effect of using date/time temporarily and use a usual QwtScaleDraw object - so, that you can compare the visual result more easily to what happens when you zoom in.
Then check what rectangles are selected by the zoomer ( use the debugger, or connect to the signals of QwtPlotZoomer/QwtPlotPicker ). Then we have more information about where to look for the problem.

Note that you are using the inofficial patch for more than 4 axes. Maybe this is a problem related to using a wrong axis index because of it.

Uwe

Hello Uwe,

If I eliminate the date/time the problem persists. The same result. I checked the rectangles and it's right. I tried to use the rectangle's first and last point as x-axis and It doesn't work. It prints as I showed before, just a small piece on the screen's center. I don't think my problem is because of the patch, because I'm using the MultiYAxis patch, I'm applying just for the y-axis, I don't have and use a patch on my x-axis. I have just the two x-axis that Qwt provides, top and bottom.

Do you have any other idea?

Thanks in advance

Please simplify your code as far as possible and find values for the scale, that you can show the problem with a simple call of setAxisScale. Then try the same with a version without using the multi-axes patch.

When the problem is still there upload your demo code as it is and I will have a look at it. If the problem is gone without the multi-axes patch upload a tarball with your patched Qwt version too.

Uwe