Axis.getHTMLImageMap

Generates an HTML image map for the axis labels.

This method should be called only after creating the chart image (eg. using BaseChart.makeChart, BaseChart.makeChart2 or BaseChart.makePicture). The image map cannot be determined without creating the chart image first.

This method accepts a URL as its argument. When generating an image map, it appends query parameters to the URL to indicate which legend entry the user has clicked.

The following is an example image map generated for an axis with 3 labels.

<area shape="rect" coords="30,220,70,239" href="handler.asp?value=0&label=John">
<area shape="rect" coords="70,220,110,239" href="handler.asp?value=1&label=Mary">
<area shape="rect" coords="110,220,150,239" href="handler.asp?value=2&label=Peter">

The image map consists of multiple <area> tags, one for each label. In the "href" attributes, query parameters are appended to the URL to provide information on the label clicked.

The image map produces by ChartDirector does not include the <map> and </map> tag. This is intentional so that you can add additional custom <area> tags to the image map, or append multiple image maps together.

The format of the appended URL parameters is determined using the queryFormat argument, which by default is:

value={value}&label={label}

The texts in curly brackets (i.e. {value}, {label}) will be replaced by the actual values when generating the image map. For example, {label} will be replaced by the label text.

Please refer to Parameter Substitution and Formatting on all available parameters and how to format them.

In addition to customizing the query parameters, ChartDirector supports additional HTML attributes in the <area> tags using the extraAttr argument.

For example, the following extraAttr will add a "title" HTML attribute to every <area> tag. The "title" attribute will be displayed as "tool tip" when the mouse moves over the image map.

title='Click me for details on {label}'

Another common usage of the extraAttr argument is to add "onmouseover" and "onmouseout" HTML attributes to handle user interaction using Javascript on the browser.

Argument	Default	Description
url	(Mandatory)	The URL to be used in the "href" attribute of the image map. Parameter Substitution and Formatting is supported. Use an empty string if no href attribute is needed.
queryFormat	""	A text string representing the template of the query parameters to be appended to the URL. Parameter Substitution and Formatting is supported. The special keyword "{default}" represents the default query parameters. This is useful for specifying appending to the default. Note that an empty string means to use the default query query parameters. To specify no query parameter, use a space character.
extraAttr	""	A text string to specify additional attributes to add to the <area> tag. Parameter Substitution and Formatting is supported.
offsetX	0	An offset to be added to all x coordinates in the image map. This is useful if the current image will be shifted and inserted into another image. In this case, the image map will need to be shifted by the same offset.
offsetY	0	An offset to be added to all y coordinates in the image map. See offsetX above for description.