gnuplot 4.6 |
53 |
Automated iteration over multiple columns
If you want to create a histogram from many columns of data in a single le, it is very convenient to use the plot iteration feature. See iteration (p. 70). For example, to create stacked histograms of the data in columns 3 through 8
set style histogram columnstacked
plot for [i=3:8] "datafile" using i title columnhead
Image
The image, rgbimage, and rgbalpha plotting styles all project a uniformly sampled grid of data values onto a plane in either 2D or 3D. The input data may be an actual bitmapped image, perhaps converted from a standard format such as PNG, or a simple array of numerical values.
This gure illustrates generation of a heat map from an array of scalar values. The current palette is used to map each value onto the color assigned to the corresponding pixel.
plot '-' matrix with image 5 4 3 1 0 2 2 0 0 1 0 0 0 1 0 0 1 2 4 3
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2D Heat map from in-line array of values |
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Each pixel (data point) of the input 2D image will be- |
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RGB image mapped onto a plane in 3D |
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come a rectangle or parallelipiped in the plot. The co- |
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ordinates of each data point will determine the center |
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of the parallelipiped. That is, an M x N set of data |
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will form an image with M x N pixels. This is di er- |
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ent from the pm3d plotting style, where an M x N set |
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of data will form a surface of (M-1) x (N-1) elements. |
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The scan directions for a binary image data grid can be |
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further controlled by additional keywords. See binary |
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keywords ipx (p. 76), keywords center (p. 76), |
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and keywords rotate (p. 76). |
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Image data can be scaled to ll a particular rectangle |
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Rescaled image used as plot element |
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within a 2D plot coordinate system by specifying the x |
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and y extent of each pixel. See binary keywords dx |
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Building Heights |
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(p. 76) and dy (p. 76). To generate the gure at the |
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by Neighborhood |
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right, the same input image was placed multiple times, |
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each with a speci ed dx, dy, and origin. The input PNG |
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image of a building is 50x128 pixels. The tall building |
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was drawn by mapping this using dx=0.5 dy=1.5. The |
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50 |
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short building used a mapping dx=0.5 dy=0.35. |
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The image style handles input pixels containing a |
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Downtown |
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NE |
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Suburbs |
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grayscale or color palette value. Thus 2D plots (plot command) require 3 columns of data (x,y,value), while 3D plots (splot command) require 4 columns of data (x,y,z,value).
The rgbimage style handles input pixels that are described by three separate values for the red, green, and blue components. Thus 5D data (x,y,r,g,b) is needed for plot and 6D data (x,y,z,r,g,b) for splot. The individual red, green, and blue components are assumed to lie in the range [0:255].
The rgbalpha style handles input pixels that contain alpha channel (transparency) information in addition to the red, green, and blue components. Thus 6D data (x,y,r,g,b,a) is needed for plot and 7D data (x,y,z,r,g,b,a) for splot. The r, g, b, and alpha components are assumed to lie in the range [0:255].