jplot

Class Axis

java.lang.Object

jplot.Axis

public class Axis
extends Object

Includes a static function for selecting and labeling graph axis tic labels. given a numeric range and a maximum number of tics, this class can produce a list of labels with the nicest round numbers not exceeding a given maximum number of labels. the label generation code was extracted from the public domain Ptolomy project at UC Berkeley, taken from ptolemy/plot/PlotBox.java. We added another static method to compute and draw an axis into a given AWT Graphics object. i extracted the code for producing linear labels and threw out the vast majority of code that attempted to produce log scale labels since that code was very broken. it was noted int the Ptolomy code that the log label generation was itself based on a file named xgraph.c by David Harrisonmy, and the comments say that the original code breaks down in certain cases. my drawAxis method can still draw nicely labeling log scale axes because i simply use the linear scale label generation code from Ptolomy and plot the tics in their proper locations on a log scale. the resulting code produced exactly the same results as the Ptolemy code for log scales in those ranges where the Ptolemy code did work, so this design is much better in all cases and uses only a fraction of the original complexity. still, it can probably be further improved though the exact problem is not well defined.

Field Summary

Fields

Modifier and Type	Field and Description
static int	X_AXIS
static int	Y_AXIS

Constructor Summary

Constructors

Constructor and Description
Axis()

Method Summary

Modifier and Type	Method and Description
static int	calculateTicNumber(double ticMinVal, double ticMaxVal, double xStep, boolean isLog) Precompute number of ticks
static double	calculateTicSep(double min, double max, int maxNumberOfTicks) Calculation of the separation length between tics.
static Vector<String>	computeTicks(double ticMinVal, double ticMaxVal, int maxTicks, boolean isLog) this is the central method of this class.
static void	drawAxis(int axis, int maxTics, int ticLength, float lowVal, float highVal, int screenStart, int screenEnd, int screenOffset, boolean logScale, int screenHeight, Graphics g) high-level method for drawing a chart axis line plus labeled tic marks.
static double	exp10(double val)
static float	fexp10(double val)
static float	flog10(double val)
static double	log10(double val)
static void	main(String[] args) simple example program for Axis class.
static int	plotValue(float val, float lowVal, float highVal, int screenStart, int screenEnd, boolean logScale, int screenHeight) lower level method to determine a screen location where a given value should be plotted given range, type, and screen information.
static Dimension	stringSize(String str, Graphics g) handy little utility for determining the length in pixels the given string will use if drawn into the given Graphics object.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

X_AXIS

public static final int X_AXIS

See Also:

Constant Field Values

Y_AXIS

public static final int Y_AXIS

See Also:

Constant Field Values

Constructor Detail

Axis

public Axis()

Method Detail

log10

public static double log10(double val)

exp10

public static double exp10(double val)

flog10

public static float flog10(double val)

fexp10

public static float fexp10(double val)

calculateTicSep

public static double calculateTicSep(double min,
                                     double max,
                                     int maxNumberOfTicks)

Calculation of the separation length between tics. Some smart rounding algorithms are needed to get the scaling properly in case of data going to 10.3 or so... Useful stuff stolen from the Gnuplot sources, thank you guys!!

calculateTicNumber

public static int calculateTicNumber(double ticMinVal,
                                     double ticMaxVal,
                                     double xStep,
                                     boolean isLog)

Precompute number of ticks

computeTicks

public static Vector<String> computeTicks(double ticMinVal,
                                          double ticMaxVal,
                                          int maxTicks,
                                          boolean isLog)

this is the central method of this class. takes axis range parameters and produces a list of string representations of nicely rounded numbers within the given range. these strings are intended for use as axis tic labels. note: to find out where to plot each tic label simply use
float ticval = Float.parseFloat(ticstring);

Parameters:

ticMinVal - no tics will be created for less than this value.

ticMaxVal - no tics will be created for greater than this value.

maxTics - returned vector will contain no more labels than this number.

isLog - set to true in case of log10 numbers

Returns:

a Vector containing formatted label strings which should also be parsable into floating point numbers (in order to plot them).

drawAxis

public static void drawAxis(int axis,
                            int maxTics,
                            int ticLength,
                            float lowVal,
                            float highVal,
                            int screenStart,
                            int screenEnd,
                            int screenOffset,
                            boolean logScale,
                            int screenHeight,
                            Graphics g)

high-level method for drawing a chart axis line plus labeled tic marks. introduces a dependancy on AWT because it takes a Graphics parameter. perhaps this method belongs in some higher-level class but i added it here since it's highly related with the tic lable generation code.

Parameters:

axis - is one of Axis.X_AXIS or Axis.Y_AXIS.

maxTics - is the maximum number of labeled tics to draw. note: the actual number drawn may be less.

lowVal - is the smallest value tic mark that may be drawn. note: the lowest valued tic label may be greater than this limit.

highVal - is the largest value tic mark that may be drawn. note: the highest valued tic label may be less than this limit.

screenStart - is the coordinate in the low valued direction.

screenEnd - is the coordinate in the high valued direction.

offset - is the coordinate in the direction perpendicular to the specified direction.

logScale - is true if a log scale axis is to be drawn, false for a linear scale.

screenHeight - is needed to flip Y coordinates.

g - is the AWT Graphics object to draw into. note: all drawing will be done in the current color of the given Graphics object.

plotValue

public static int plotValue(float val,
                            float lowVal,
                            float highVal,
                            int screenStart,
                            int screenEnd,
                            boolean logScale,
                            int screenHeight)

lower level method to determine a screen location where a given value should be plotted given range, type, and screen information. the "val" parameter is the data value to be plotted

Parameters:

val - is a data value to be plotted.

Returns:

pixel offset (row or column) to draw a screen representation of the given data value. i.e. where along an axis in screen coordinates the caller should draw a representation of the given value.

See Also:

drawAxis(int,int,int,float,float,int,int,int,boolean,int,Graphics)

stringSize

public static Dimension stringSize(String str,
                                   Graphics g)

handy little utility for determining the length in pixels the given string will use if drawn into the given Graphics object. Note: perhaps belongs in some utility package.

main

public static void main(String[] args)

simple example program for Axis class.