Using QwtRasterData for displaying the raster data resultant from R language

From here:http://cran.r-project.org/web/packages/ggmap/ggmap.pdf

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ggmap plots the raster object produced by get_map.

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From: http://qwt.sourceforge.net/class_qwt_raster_data.html

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QwtRasterData defines an interface to any type of raster data

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So, following way the data resultant from get_map is saved in a rda (raster) file.

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mapImageData <- get_googlemap (c (lon=-74.0087986666667, lat=40.7106593333333), zoom=15)
save (mapImageData, file="savedMap.rda")

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Will it be possible for me to display that resultant raster data on QwtRasterData class?

• What more information should I present here to know whether it can be done and how?
• Should I present a sample of raster data?
• Do I need to convert that raster data in a particular format before it can be loaded on the Qt widget?

QwtRasterData assumes that you have a regular matrix of data values, one for every cell in the matrix. It then maps this (x,y,z) data to a spectrogram using bilinear interpolation to create colors for the pixels between raster points. QwtRasterData doesn't display anything; QwtPlotSpectrogram does that, using the data in QwtRasterData.

So, you need to parse the rda into a QwtRasterData structure, then decide on the color mapping to be used for displaying the spectrogram. Note that for the color mapping to work properly, you must set the z range such that min z and max z map to 0 and 1 on the color map, respectively.

I have no idea what an rda file looks like, so you will have to determine how to parse it.

And you probably want to use QwtMatrixRasterData; parse your rda file into a QVector< double > array of size (nRows * nCols), where each value in the vector is the value of z at that point. Use the "setValueMatrix()" and "setInterval()" methods to define the real-world x- and y-ranges of the data so the spectrogram can plot it properly.

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QwtRasterData assumes that you have a regular matrix of data values, one for every cell in the matrix. It then maps this (x,y,z) data to a spectrogram using bilinear interpolation to create colors for the pixels between raster points.

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This is what QwtMatrixRasterData does. QwtRasterData is simply an abstract API to bind the data ( however it looks like ) to a spectrogram.

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So, you need to parse the rda into a QwtRasterData structure, ...

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All what needs to be done is to implement the abstract methods usually fetching the values from any applications specific data structures.

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And you probably want to use QwtMatrixRasterData; parse your rda file into a QVector< double > array of size (nRows * nCols) ...

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When there is no other reason to have the values in memory this should be the easiest way to go.

Uwe