Re: QwtPlotMarker/QwtLogScaleEngine conflict

[wreiter <wol...@wi...>]

On 25.01.19 12:42, Uwe Rathmann wrote:
> Hi Wolfgang,
>
>> The initial coordinates are set to (0, 0) which is certainly inside 
>> the axis-range 
>
> No, 0 is not a valid value for a logarithmic scale - due to its nature.
> Start the bode example, press zoom and pan on the canvas towards 
> smaller values - you will see, why you will never reach 0.0.
> If you need to have the 0 you need to write a tranformation, that is 
> linear in some range around 0 ( f.e [-1, 1 ] ) and logarithmic 
> otherwise. But this more advanced stuff.
>
> Of course you could also use a transformation based on pow(10). This 
> has a similar effect, but it can pass 0 out of the box. See 
> https://qwt.sourceforge.io/class_qwt_power_transform.html
>
> Uwe
>
>
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Hello Uwe,


you are correct, this clears up the misunderstanding of the 
QwtScaleEngine. Making the marker logic aware of the current axis 
scaling solves the problem.


Best regards


  --
Wolfgang Reiter
Research & Development
Wintegral GmbH

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