It is possible to combine the individual data points with a line - a link. The properties for this link can be accessed by using the instance variable ScatterPlot::link.In order to enable the link the method ScatterPlot::link::Show() must first be called.

The properties that can be adjusted are the normal line properties, i.e. weight, color and line style. The following code snippet shows how to add a link line with a dotted style drawn in black to scatter plot.

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<?php
// Enable the link lines
$scatterplot->link->Show();
 
// Set the properties
$scatterplot->link->SetWeigth(1);
$scatterplot->link->SetColor('black');
$scatterplot->link->SetStyle('dotted');
?>

In Figure 15.67. Combining data points with a dotted line (scatterlinkex3.php) and Figure 15.68. Combining data points with a red line (scatterlinkex4.php) there are two variants of adding a link line to a scatter plot. For those figures we have also used two of the predefined scientific axis styles (see Predefined scientific axis setups).

Figure 15.67. Combining data points with a dotted line (scatterlinkex3.php)

Figure 15.68. Combining data points with a red line (scatterlinkex4.php)

A variant of scatter plots often used electrical engineering is the stem plot as shown in Figure 15.56. Supported pattern fills for bar plots

Figure 15.69. Stem plot (impulsex1.php)

This variant of the scatter plot is created by calling the method

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$scatterplot->SetStem();

In order to adjust the look and feel of the stems the following methods can be used

Another example of stem plot is shown in Figure 15.70. Adjusting the overall look and feel for the stem graph (impulsex3.php) where we have adjusted both the look and feel of the stem plot as well as the position of the x-axis.

Figure 15.70. Adjusting the overall look and feel for the stem graph (impulsex3.php)

There is also another complex impulse example shown in Figure 14.58. Adding a static line at y=0 to simulate an extra 0-axis (impulsex4.php) where we have used a PlotLine to create a "virtual" x-axis.

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 and angle).

A field plot is created as an instance of class FieldPlot with three argument

as the following code snippet shows

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$fieldplot = new FieldPlot($datay, $datax, $angle);

The size and color of each arrow in the field plot is controlled by accessing the property FieldPlot::arrow and using the two methods

Another way to individually format each arrow is to use a callback method. The callback method must have three arguments x- , y-coordinates and angle. The callback method must return an array with three elements (color,size,arrow size). The callback method is specified by calling

Figure 15.72. A field plot (fieldscatterex1.php) shows a field plot with a callback function.

Figure 15.72. A field plot (fieldscatterex1.php)

This is a variant of scatter plot where each data point is a filled circle and the size of the circle is dynamically adjusted. This makes it possible to display three values at each data point (x,y,"size"). There is no need for a specific plot type for this since these types of plots can be constructed with an ordinary scatter plot and a mark formatting callback.

In order to specify a callback for the marks the following method is used

We can now create a balloon plot as follows.

As an optional additions we can also enable the display of the values at each data point by calling

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$sp1->value->Show();
$sp1->value->SetFont(FF_FONT1,FS_BOLD);

Putting all these together gives the result shown in Figure 15.73. Using format callback to create a balloon plot (balloonex2.php)

Figure 15.73. Using format callback to create a balloon plot (balloonex2.php)

Geo-maps (a.k.a. Geo-charts, push-pin graphs) is used to illustrate locations around the world by putting markers on a flat projection of the earth. A Geo-map is done by adding a Worldmap background to a standard scatter graph. The library includes a suitable background in the "Examples/" directory "wordmap1.jpg". This can then be done as the following example shows

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<?php // content="text/plain; charset=utf-8"
require_once ('jpgraph/jpgraph.php');
require_once ('jpgraph/jpgraph_scatter.php');
 
DEFINE('WORLDMAP','worldmap1.jpg');
 
function markCallback($y,$x) {
    // Return array width
    // width,color,fill color, marker filename, imgscale
    // any value can be false, in that case the default value will
    // be used.
    // We only make one pushpin another color
    if( $x == 54 ) 
    return array(false,false,false,'red',0.8);
    else
    return array(false,false,false,'green',0.8);
}
 
// Data arrays
$datax = array(10,20,30,40,54,60,70,80);
$datay = array(12,23,65,18,84,28,86,44);
 
// Setup the graph
$graph = new Graph(400,270);
 
// We add a small 1pixel left,right,bottom margin so the plot area
// doesn't cover the frame around the graph.
$graph->img->SetMargin(1,1,1,1);
$graph->SetScale('linlin',0,100,0,100);
 
// We don't want any axis to be shown
$graph->xaxis->Hide();
$graph->yaxis->Hide();
 
// Use a worldmap as the background and let it fill the plot area
$graph->SetBackgroundImage(WORLDMAP,BGIMG_FILLPLOT);
 
// Setup a nice title with a striped bevel background
$graph->title->Set("Pushpin graph");
$graph->title->SetFont(FF_ARIAL,FS_BOLD,16);
$graph->title->SetColor('white');
$graph->SetTitleBackground('darkgreen',TITLEBKG_STYLE1,TITLEBKG_FRAME_BEVEL);
$graph->SetTitleBackgroundFillStyle(TITLEBKG_FILLSTYLE_HSTRIPED,'blue','darkgreen');
 
// Finally create the scatterplot
$sp = new ScatterPlot($datay,$datax);
 
// We want the markers to be an image
$sp->mark->SetType(MARK_IMG_PUSHPIN,'blue',0.6);
 
// Install the Y-X callback for the markers
$sp->mark->SetCallbackYX('markCallback');
 
// ...  and add it to the graph
$graph->Add($sp);    
 
// .. and output to browser
$graph->Stroke();
 
?>

Figure 15.74. An example with geo maps (pushpinex1.php)

Another example of using worldmaps with Pie graphs is shown in Adding background images to Pie graphs