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Thread: qwt log scale Y and linear scale X

  1. #1
    Join Date
    Feb 2010
    Russia, Omsk
    Qt products

    Default qwt log scale Y and linear scale X

    Hello. How can I do the next:
    I understand that I need to use QwtLog10ScaleEngine but how?


  2. #2
    Join Date
    Feb 2006
    Munich, Germany
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    Qt3 Qt4 Qt/Embedded
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    Default Re: qwt log scale Y and linear scale X

    The plot on the screenshot is not logarithmic base 10 - so QwtLog10ScaleEngine won't help.

    You need to use Qwt 6.1 ( from SVN trunk or wait until end of this week ). Here you can add your own type of transformation ( QwtTransform ) - but of course you need to understand the transformation used in the screenshot first. For me it looks more like QwtPowerTransform than QwtLogTransform. ( the playground/scaleengine you find an application that plays with transformations - click on the legend to see the effect )

    Another problem is that the axis values are not unique - each value can be found in the upper and in the lower half. But as you know where to put a curve point there seems to be another hidden coordinate system for the y values behind.

    So these are the steps you need to start with:

    • Identify the real coordinate system and how to map coordinates into the systems on the y axes
    • Find the transformation used for each axis


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