QwtContouring question

how can I get the data value at a given (X, Y) point in QwtRasterData? This (x, Y) may not be one of the points in QwtRasterData value( x, y ) interface...In another word, is it possible to do cursor tracking on QwtRasterData?

Thanks

QwtRasterData::value(...) returns a value for all x/y positions inside the bounding rectangle. This is how it is defined - otherwise your implementation is insufficient.

A QwtRasterData object that sits on a 2 dimensional array always has to do an internal resampling ( in most cases simply next neighbour ) because the pixel positions never meet the raster.

Uwe

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Originally Posted by Uwe

QwtRasterData::value(...) returns a value for all x/y positions inside the bounding rectangle. This is how it is defined - otherwise your implementation is insufficient.

A QwtRasterData object that sits on a 2 dimensional array always has to do an internal resampling ( in most cases simply next neighbour ) because the pixel positions never meet the raster.

Uwe

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Hmmm, I lost my reply made yesterday...

From your internal resampling data, can I get back your resampled value at location (x, y)? If so, how?

Thanks

The scaleMaps ( QwtPlot::canvasMap() ) translate between pixel and plot coordinates. If you use a QwtPlotPicker (overload QwtPlotPicker::trackerText() ) the picker does the translation for you.

Uwe

Quote:

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Originally Posted by Uwe

The scaleMaps ( QwtPlot::canvasMap() ) translate between pixel and plot coordinates. If you use a QwtPlotPicker (overload QwtPlotPicker::trackerText() ) the picker does the translation for you.

Uwe

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I don't need the coordinate, I need the value at the coordinate. That said, I give you the coordinate, and I need the contour or raster data value at that coordinate. Can that be done?

Thanks.

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Originally Posted by lni

That said, I give you the coordinate, and I need the contour or raster data value at that coordinate.

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This is QwtRasterData::value(double, double).

Uwe

Quote:

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Originally Posted by Uwe

This is QwtRasterData::value(double, double).

Uwe

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What I want to know is if you can return me the sampled value at location not in value(x, y), value( x, y) is what I give to you so there is no reason for me to ask for that.

I want to know if you can give me value( x + dx, y + dy )...thanks

Quote:

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Originally Posted by lni

I want to know if you can give me value( x + dx, y + dy )

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Qwt has no samples at all. It can't give you no value at no position. The only one who knows them is your implementation of QwtRasterData. What's so hard with accepting this ?

What Qwt knows is the coordinate system and how to translate it to pixel positions. I don't know what dx/dy is supposed to be, but maybe this is what your question is about ?

Uwe