Plotchart is a Tcl-only package that focuses on the easy creation of xy-plots, barcharts and other common types of graphical presentations. The emphasis is on ease of use, rather than flexibility. The procedures that create a plot use the entire canvas window, making the layout of the plot completely automatic.

This results in the creation of an xy-plot in, say, ten lines of code:

    package require Plotchart

    canvas .c -background white -width 400 -height 200
    pack   .c -fill both

    #
    # Create the plot with its x- and y-axes
    #
    set s [::Plotchart::createXYPlot .c {0.0 100.0 10.0} {0.0 100.0 20.0}]

    foreach {x y} {0.0 32.0 10.0 50.0 25.0 60.0 78.0 11.0 } {
        $s plot series1 $x $y
    }

    $s title "Data series"

A drawback of the package might be that it does not do any data management. So if the canvas that holds the plot is to be resized, the whole plot must be redrawn. The advantage, though, is that it offers a number of plot and chart types:

XY-plots like the one shown above with any number of data series.
Stripcharts, a kind of XY-plots where the horizontal axis is adjusted automatically. The result is a kind of sliding window on the data series.
Polar plots, where the coordinates are polar instead of cartesian.
Isometric plots, where the scale of the coordinates in the two directions is always the same, i.e. a circle in world coordinates appears as a circle on the screen.

You can zoom in and out, as well as pan with these plots (Note: this works best if no axes are drawn, the zooming and panning routines do not distinguish the axes), using the mouse buttons with the control key and the arrow keys with the control key.
Piecharts, with automatic scaling to indicate the proportions.
Barcharts, with either vertical or horizontal bars, stacked bars or bars side by side.
Timecharts, where bars indicate a time period and milestones or other important moments in time are represented by triangles.
3D plots (both for displaying surfaces and 3D bars)

PLOT CREATION COMMANDS

You create the plot or chart with one single command and then fill the plot with data:

::Plotchart::createXYPlot w xaxis yaxis

Create a new xy-plot.

widget w (in): Name of the existing canvas widget to hold the plot.
list xaxis (in): A 3-element list containing minimum, maximum and stepsize for the x-axis, in this order.
list yaxis (in): A 3-element list containing minimum, maximum and stepsize for the y-axis, in this order.

::Plotchart::createStripchart w xaxis yaxis

Create a new strip chart. The only difference to a regular XY plot is that the x-axis will be automatically adjusted when the x-coordinate of a new point exceeds the maximum.

widget w (in): Name of the existing canvas widget to hold the plot.
list xaxis (in): A 3-element list containing minimum, maximum and stepsize for the x-axis, in this order.
list yaxis (in): A 3-element list containing minimum, maximum and stepsize for the y-axis, in this order.

::Plotchart::createPolarPlot w radius_data

Create a new polar plot.

widget w (in): Name of the existing canvas widget to hold the plot.
list radius_data (in): A 2-element list containing maximum radius and stepsize for the radial axis, in this order.

::Plotchart::createIsometricPlot w xaxis yaxis stepsize

Create a new isometric plot, where the vertical and the horizontal coordinates are scaled so that a circle will truly appear as a circle.

widget w (in): Name of the existing canvas widget to hold the plot.
list xaxis (in): A 2-element list containing minimum, and maximum for the x-axis, in this order.
list yaxis (in): A 2-element list containing minimum, and maximum for the y-axis, in this order.
float|noaxes stepsize (in): Either the stepsize used by both axes or the keyword noaxes to signal the plot that it should use the full area of the widget, to not draw any of the axes.

::Plotchart::create3DPlot w xaxis yaxis zaxis

Create a new 3D plot.

widget w (in): Name of the existing canvas widget to hold the plot.
list xaxis (in): A 3-element list containing minimum, maximum and stepsize for the x-axis, in this order.
list yaxis (in): A 3-element list containing minimum, maximum and stepsize for the y-axis, in this order.
list zaxis (in): A 3-element list containing minimum, maximum and stepsize for the z-axis, in this order.

::Plotchart::createPiechart w

Create a new piechart.

widget w (in): Name of the existing canvas widget to hold the plot.

::Plotchart::createBarchart w xlabels yaxis noseries

Create a new barchart with vertical bars. The horizontal axis will display the labels contained in the argument xlabels. The number of series given by noseries determines both the width of the bars, and the way the series will be drawn.

If the keyword stacked was specified the series will be drawn stacked on top of each other. Otherwise each series that is drawn will be drawn shifted to the right.

widget w (in): Name of the existing canvas widget to hold the plot.
list xlabels (in): List of labels for the x-axis. Its length also determines the number of bars that will be plotted per series.
list yaxis (in): A 3-element list containing minimum, maximum and stepsize for the y-axis, in this order.
int|stacked noseries (in): The number of data series that will be plotted. This has to be an integer number greater than zero (if stacked is not used).

::Plotchart::createHorizontalBarchart w xlabels yaxis noseries

Create a new barchart with horizontal bars. The vertical axis will display the labels contained in the argument ylabels. The number of series given by noseries determines both the width of the bars, and the way the series will be drawn.

If the keyword stacked was specified the series will be drawn stacked from left to right. Otherwise each series that is drawn will be drawn shifted upward.

widget w (in): Name of the existing canvas widget to hold the plot.
list ylabels (in): List of labels for the y-axis. Its length also determines the number of bars that will be plotted per series.
list yaxis (in): A 3-element list containing minimum, maximum and stepsize for the x-axis, in this order.
int|stacked noseries (in): The number of data series that will be plotted. This has to be an integer number greater than zero (if stacked is not used).

::Plotchart::createTimechart w time_begin time_end noitems

Create a new timechart. The time axis (= x-axis) goes from time_begin to time_end, and the vertical spacing is determined by the number of items to plot.

widget w (in): Name of the existing canvas widget to hold the plot.
string time_begin (in): The start time given in a form that is recognised by the clock scan command (e.g. "1 january 2004").
string time_end (in): The end time given in a form that is recognised by the clock scan command (e.g. "1 january 2004").
int noitems (in): Expected/maximum number of items. This determines the vertical spacing.

PLOT METHODS

Each of the creation commands explained in the last section returns the name of a new object command that can be used to manipulate the plot or chart. The subcommands available to a chart command depend on the type of the chart.

General subcommands for all types of charts. $anyplot is the command returned by the creation command:

$anyplot title text

Specify the title of the whole chart.

string text (in): The text of the title to be drawn.

$anyplot saveplot filename

Draws the plot into a file, using PostScript.

string filename (in): Contain the path name of the file to write the plot to.

$anyplot xtext text

Specify the title of the x-axis, for those plots that have a straight x-axis.

string text (in): The text of the x-axis label to be drawn.

$anyplot ytext text

Specify the title of the y-axis, for those plots that have a straight y-axis.

string text (in): The text of the y-axis label to be drawn.

$anyplot xconfig -option value ...

Set one or more configuration parameters for the x-axis. The following options are known:

format fmt: The format for the numbers along the axis.
ticklength length: The length of the tickmarks (in pixels).
ticklines boolean: Whether to draw ticklines (true) or not (false).
scale scale_data: New scale data for the axis, i.e. a 3-element list containing minimum, maximum and stepsize for the axis, in this order.

Beware: Setting this option will clear all data from the plot.

$anyplot yconfig -option value ...

Set one or more configuration parameters for the y-axis. This method accepts the same options and values as the method xconfig.

Note: The commands xconfig and yconfig are currently implemented only for XY-plots and only the option -format has any effect.

For xy plots and stripcharts:

$xyplot plot series xcrd ycrd

Add a data point to the plot.

string series (in): Name of the data series the new point belongs to.
float xcrd (in): X-coordinate of the new point.
float ycrd (in): Y-coordinate of the new point.

For polar plots:

$polarplot plot series radius angle

Add a data point to the polar plot.

string series (in): Name of the data series the new point belongs to.
float radius (in): Radial coordinate of the new point.
float angle (in): Angular coordinate of the new point (in degrees).

For 3D plots:

$plot3d plotfunc function

Plot a function defined over two variables x and y. The resolution is determined by the set grid sizes (see the method gridsize for more information).

string function (in): Name of the procedure that calculates the z-value for the given x and y coordinates. The procedure has to accept two float arguments (x is first argument, y is second) and return a floating-point value.

$plot3d gridsize nxcells nycells

Set the grid size in the two directions. Together they determine how many polygons will be drawn for a function plot.

int nxcells (in): Number of grid cells in x direction. Has to be an integer number greater than zero.
int nycells (in): Number of grid cells in y direction. Has to be an integer number greater than zero.

$plot3d plotdata data

Plot a matrix of data.

list data (in)

The data to be plotted. The data has to be provided as a nested list with 2 levels. The outer list contains rows, drawn in y-direction, and each row is a list whose elements are drawn in x-direction, for the columns. Example:

    set data {
    {1.0 2.0 3.0}
    {4.0 5.0 6.0}
    }

$plot3d colours fill border

Configure the colours to use for polygon borders and inner area.

color fill (in): The colour to use for filling the polygons.
color border (in): The colour to use for the border of the polygons.

For xy plots, stripcharts and polar plots:

$xyplot dataconfig series -option value ...

Set the value for one or more options regarding the drawing of data of a specific series.

string series (in): Name of the data series whose configuration we are changing.

The following option are known:

colour c
color c: The colour to be used when drawing the data series.
type enum: The drawing mode chosen for the series. This can be one of line, symbol, or both.
symbol enum: What kind of symbol to draw. The value of this option is ignored when the drawing mode line was chosen. This can be one of plus, cross, circle, up (triangle pointing up), down (triangle pointing down), dot (filled circle), upfilled or downfilled (filled triangles).

For piecharts:

$pie plot data

Fill a piechart.

list data (in): A list of pairs (labels and values). The values determine the relative size of the circle segments. The labels are drawn beside the circle.

$pie colours colour1 colour2 ...

Set the colours to be used.

color colour1 (in): The first colour.
color colour2 (in): The second colour, and so on.

For vertical barcharts:

$barchart plot series ydata colour

Add a data series to a barchart.

string series (in): Name of the series the values belong to.
list ydata (in): A list of values, one for each x-axis label.
color colour (in): The colour of the bars.

For horizontal barcharts:

$barchart plot series xdata colour

Add a data series to a barchart.

string series (in): Name of the series the values belong to.
list xdata (in): A list of values, one for each y-axis label.
color colour (in): The colour of the bars.

For timecharts:

$timechart period text time_begin time_end colour

Add a time period to the chart.

string text (in): The text describing the period.
string time_begin (in): Start time of the period.
string time_end (in): Stop time of the period.
color colour (in): The colour of the bar (defaults to black).

$timechart milestone text time colour

Add a milestone (represented as an point-down triangle) to the chart.

string text (in): The text describing the milestone.
string time (in): Time at which the milestone must be positioned.
color colour (in): The colour of the triangle (defaults to black).

$timechart vertline text time

Add a vertical line (to indicate the start of the month for instance) to the chart.

string text (in): The text appearing at the top (an abbreviation of the date/time for instance).
string time (in): Time at which the line must be positioned.

For isometric plots (to be extended):

$isoplot plot rectangle x1 y1 x2 y2 colour

Plot the outlines of a rectangle.

float x1 (in): Minimum x coordinate of the rectangle to be drawn.
float y1 (in): Minimum y coordinate of the rectangle.
float x2 (in): Maximum x coordinate of the rectangle to be drawn.
float y2 (in): Maximum y coordinate of the rectangle.
color colour (in): The colour of the rectangle.

$isoplot plot filled-rectangle x1 y1 x2 y2 colour

Plot a rectangle filled with the given colour.

float x1 (in): Minimum x coordinate of the rectangle to be drawn.
float y1 (in): Minimum y coordinate of the rectangle.
float x2 (in): Maximum x coordinate of the rectangle to be drawn.
float y2 (in): Maximum y coordinate of the rectangle.
color colour (in): The colour of the rectangle.

$isoplot plot circle xc yc radius colour

Plot the outline of a circle.

float xc (in): X coordinate of the circle's centre.
float yc (in): Y coordinate of the circle's centre.
color colour (in): The colour of the circle.

$isoplot plot filled-circle xc yc radius colour

Plot a circle filled with the given colour.

float xc (in): X coordinate of the circle's centre.
float yc (in): Y coordinate of the circle's centre.
color colour (in): The colour of the circle.

There are a number of public procedures that may be useful in specific situations: Pro memorie.

COORDINATE TRANSFORMATIONS

Besides the commands that deal with the plots and charts directly, there are a number of commands that can be used to convert world coordinates to pixels and vice versa. These include:

::Plotchart::viewPort w pxmin pymin pxmax pymax

Set the viewport for window w. Should be used in cooperation with ::Plotchart::worldCoordinates.

widget w (in): Name of the window (canvas widget) in question.
float pxmin (in): Left-most pixel coordinate.
float pymin (in): Top-most pixel coordinate (remember: the vertical pixel coordinate starts with 0 at the top!).
float pxmax (in): Right-most pixel coordinate.
float pymax (in): Bottom-most pixel coordinate.

::Plotchart::worldCoordinates w xmin ymin xmax ymax

Set the extreme world coordinates for window w. The world coordinates need not be in ascending order (i.e. xmin can be larger than xmax, so that a reversal of the x-axis is achieved).

widget w (in): Name of the window (canvas widget) in question.
float xmin (in): X-coordinate to be mapped to left side of viewport.
float ymin (in): Y-coordinate to be mapped to bottom of viewport.
float xmax (in): X-coordinate to be mapped to right side of viewport.
float ymax (in): Y-coordinate to be mapped to top side of viewport.

::Plotchart::world3DCoordinates w xmin ymin zmin xmax ymax zmax

Set the extreme three-dimensional world coordinates for window w. The world coordinates need not be in ascending order (i.e. xmin can be larger than xmax, so that a reversal of the x-axis is achieved).

widget w (in): Name of the window (canvas widget) in question.
float xmin (in): X-coordinate to be mapped to front side of the 3D viewport.
float ymin (in): Y-coordinate to be mapped to left side of the viewport.
float zmin (in): Z-coordinate to be mapped to bottom of viewport.
float xmax (in): X-coordinate to be mapped to back side of viewport.
float ymax (in): Y-coordinate to be mapped to right side of viewport.
float zmax (in): Z-coordinate to be mapped to top side of viewport.

::Plotchart::coordsToPixel w x y

Return a list of pixel coordinates valid for the given window.

widget w (in): Name of the window (canvas widget) in question.
float x (in): X-coordinate to be mapped.
float y (in): Y-coordinate to be mapped.

::Plotchart::coords3DToPixel w x y z

Return a list of pixel coordinates valid for the given window.

widget w (in): Name of the window (canvas widget) in question.
float x (in): X-coordinate to be mapped.
float y (in): Y-coordinate to be mapped.
float y (in): Z-coordinate to be mapped.

::Plotchart::polarCoordinates w radmax

Set the extreme polar coordinates for window w. The angle always runs from 0 to 360 degrees and the radius starts at 0. Hence you only need to give the maximum radius. Note: If the viewport is not square, this procedure will not adjust the extremes, so that would result in an elliptical plot. The creation routine for a polar plot always determines a square viewport.

widget w (in): Name of the window (canvas widget) in question.
float radmax (in): Maximum radius.

::Plotchart::polarToPixel w rad phi

Wrapper for a call to ::Plotchart::coordsToPixel, which assumes the world coordinates and viewport are set appropriately. Converts polar coordinates to pixel coordinates. Note: To be useful it should be accompanied by a matching ::Plotchart::worldCoordinates procedure. This is automatically taken care of in the creation routine for polar plots.

widget w (in): Name of the window (canvas widget) in question.
float rad (in): Radius of the point.
float phi (in): Angle to the positive x-axis.

::Plotchart::pixelToCoords w x y

Return a list of world coordinates valid for the given window.

widget w (in): Name of the window (canvas widget) in question.
float x (in): X-pixel to be mapped.
float y (in): Y-pixel to be mapped.

::Plotchart::pixelToIndex w x y

Return the index of the pie segment containing the pixel coordinates (x,y)

widget w (in): Name of the window (canvas widget) in question, holding a piechart.
float x (in): X-pixel to be mapped.
float y (in): Y-pixel to be mapped.

Furthermore there is a routine to determine "pretty" numbers for use with an axis:

::Plotchart::determineScale xmin xmax

Determine "pretty" numbers from the given range and return a list containing the minimum, maximum and stepsize that can be used for a (linear) axis.

float xmin (in): Rough minimum value for the scaling
float xmax (in): Rough maximum value for the scaling.

OTHER OUTPUT FORMATS

Besides output to the canvas on screen, the module is capable, via canvas postscript, of producing PostScript files. One may wonder whether it is possible to extend this set of output formats and the answer is "yes". This section tries to sum up the aspects of using this module for another sort of output.

One way you can create output files in a different format, is by examining the contents of the canvas after everything has been drawn and render that contents in the right form. This is probably the easiest way, as it involves nothing more than the re-creation of all the elements in the plot that are already there.

The drawback of that method is that you need to have a display, which is not always the case if you run a CGI server or something like that.

An alternative is to emulate the canvas command. For this to work, you need to know which canvas subcommands are used and what for. Obviously, the create subcommand is used to create the lines, texts and other items. But also the raise and lower subcommands are used, because with these the module can influence the drawing order - important to simulate a clipping rectangle around the axes. (The routine DrawMask is responsible for this - if the output format supports proper clipping areas, then a redefinition of this routine might just solve this).

Furthermore, the module uses the cget subcommand to find out the sizes of the canvas. A more mundane aspect of this is that the module currently assumes that the text is 14 pixels high and that 80 pixels in width suffice for the axis' labels. No "hook" is provided to customise this.

In summary:

Emulate the create subcommand to create all the items in the correct format
Emulate the cget subcommand for the options -width and -height to allow the correct calculation of the rectangle's position and size
Solve the problem of raising and lowering the items so that they are properly clipped, for instance by redefining the routine DrawMask.
Take care of the currently fixed text size properties

ROOM FOR IMPROVEMENT

In this version there are a lot of things that still need to be implemented:

General options like legends and text to the axes.
More robust handling of incorrect calls (right now the procedures may fail when called incorrectly):
- The axis drawing routines can not handle inverse axes right now.
- If the user provides an invalid date/time string, the routines simply throw an error.

TODO - SOME PRIVATE NOTES

I have the following wishlist:

Isometric plots - allow new items to be implemented easily.
Add support for histograms where the independent axis is numerical.
A general 3D viewer - emphasis on geometry, not a ray-tracer.

KEYWORDS

3D bars , 3D surfaces , bar charts , charts , coordinate transformations , coordinates , graphical presentation , isometric plots , pie charts , plotting , polar plots , strip charts , time charts , xy-plots

Plotchart(n) 0.9 "Plotchart"

Copyright © 2004 for compilation: ActiveState