CLASS FieldPlot EXTENDS Plot
(Defined in: jpgraph_scatter.php : 63)
 FieldPlot Plot FieldPlot()   SetCallback()

Class usage and Overview
A variant of scatter plot is the so called Field Plots this is basically a scatter plot where each scatter point is an arrow with a direction between 0 to 359 degrees. This effectively allows the visualization of 3 parameters at each point (x,y,angle). As an additional bonus there is also possible to define a callback for each scatter plot to also define the color for each point.

See also related classes:
FieldArrow

Class Methods

function FieldPlot(\$datay,\$datax,\$angles)
Create an instance of FieldPlot

ArgumentDefaultDescription
\$datay  Y-coordinate
\$datax  X-coordinate
\$angles  Angle

Description
Create a new instance of a field plot

Example

\$fp = new FieldPlot(\$datay,\$datax,\$angle);

function SetCallback(\$aFunc)
Specify callback for each arrow in the field plot

ArgumentDefaultDescription
\$aFunc  Function name

Description
Specify a callback that gets clled for each arrow in the field plot The callback should return an array with the elements
1. Color
2. Size of arrow (in pixels)
3. Arrow head size (as integer between0 and 9)

Example

// Gradient. Make the arrows red at the pole and colder (blue)
// teh further we get from the pole
function FldCallback(\$x,\$y,\$a) {
\$polex=4;
\$poley=40;
\$maxr = 3000;

// Size and arrow size is constant
\$size="";
\$arrowsize="";

// Since we have different scales we need the data points
// to be of the same magnitude to give it a distance
// interpretation.
\$x *= 10;

// Colors gets colder the further out we go from the center
\$r = (\$x-\$polex*10)*(\$x-\$polex*10)+(\$y-\$poley)*(\$y-\$poley);
\$f = \$r/\$maxr;
if( \$f > 1 ) \$f=1;
\$red = floor((1-\$f)*255);
\$blue = floor(\$f*255);
\$color = array(\$red,0,\$blue);
return array(\$color,\$size,\$arrowsize);
}

// Setup the field plot
\$fp = new FieldPlot(\$datay,\$datax,\$angle);

// Setup formatting callback
\$fp->SetCallback('FldCallback');