Using QwtRasterData for displaying the raster data resultant from R language

[TheIndependentAquarius]

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

ggmap plots the raster object produced by get_map.

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

QwtRasterData defines an interface to any type of raster data

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

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

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?

[d_stranz]

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.

[Uwe]

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.

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

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

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

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

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

Uwe