QwtSymbol problem

[lin3398032]

Hi,

How to set limit symbol number in the curve?

I created symbol in my curve like below.

curve->setSymbol( new QwtSymbol( QwtSymbol::Style(1) ,
				QBrush( curveColor ), QPen( curveColor ),       
				QSize( 3.0, 3.0 ) ) );

curve->setSymbol( new QwtSymbol( QwtSymbol::Style(1) ,
				QBrush( curveColor ), QPen( curveColor ),       
				QSize( 3.0, 3.0 ) ) );

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When I show the curve, it appears thousand of symbols in my curve. Like below picture.
Capture.jpg

But, I only want to show 20 symbol in my curve. How to implement it?

Thanks a lot!