The TrendLayer class represents trend layers. TrendLayer is a subclass Layer.

TrendLayer objects are created by using XYChart.addTrendLayer and XYChart.addTrendLayer2.

The trend layer performs linear regression analysis on the data points, and represents the result as a best fit straight line with optional confidence and prediction bands.

In linear regression analysis, the data points are assumed to be related by:


where m and c are constants, and err is a randam variable.

Linear regression analysis estimates m, c and err based on available data using the least square method. Using estimated values of m and c, the line y = m * x + c are plotted as the best fit straight line based on available data.

However, as m and c are estimations based on available data, it may not be exactly equal to the "real" m and c. In ChartDirector, the uncertainties are represented visually as a confidence band around the regression line. For example, the 95% confidence band means there are 95% probability that the "real" line is in that band.

To predict a data point (infer y given x), we can use the formula:


based on estimated values of m, c and err.

The uncertainties of the data point is contributed by the uncertainties in m and c, as well as err. In ChartDirector, the uncertainties of the data points are represented visually as a prediction band around the regression line. For example, a 95% prediction band means there are 95% probability that a data point will be in that band.

The prediction band is always wider than the confidence band. It is because the uncertainties of the regression line is contributed by m and c, while the uncertainties of the data points are contributed by m, c and err. The err term makes the data points less certain that the regression line.

Method	Inherited	Description
getSlope	(Self)	Get the slope of the trend line.
getIntercept	(Self)	Get the y-axis intercept of the trend line.
getCorrelation	(Self)	Get the correlation coefficient of the trend line.
getStdError	(Self)	Get the standard error of the trend line.
addConfidenceBand	(Self)	Add a confidence band to the trend layer.
addPredictionBand	(Self)	Add a prediction band to the trend layer.
setImageMapWidth	(Self)	Set the effective width of the line used for producing image maps.
getLine	(Self)	Retrieve an opaque LineObj representing the trend line. The opaque LineObj is to be used in XYChart.addInterLineLayer for adding coloring between lines.
set3D	Layer	Set the 3D depth of the layer, and the 3D gap between the current layer and the next layer.
setLineWidth	Layer	Set the default line width of lines when drawing data sets on the layer.
setBorderColor	Layer	Set the default border color and 3D raised effect when drawing data sets on the layer.
setLegend	Layer	Set the order of the data set names when entered into the legend box.
setDataCombineMethod	Layer	Set the method used to combine multiple data sets in a layer.
addDataSet	Layer	Add a data set to the chart layer.
addDataGroup	Layer	Open a new data group.
addExtraField	Layer	Associate an extra text to each data item or data set.
getDataSet	Layer	Get the requested DataSet object.
setUseYAxis2	Layer	Determine if the primary or secondary y-axis should be used when drawing the data sets.
setXData	Layer	Set the x values of the data points in the data sets.
setXData2	Layer	Set the x values of the data points in the data sets as evenly distributed in a range.
getXCoor	Layer	Get the x coordinate of a point given the x value.
getYCoor	Layer	Get the y coordinate of a point given the y value.
xZoneColor	Layer	Create a x-zone color. A x-zone will change from one color to another depending on a threshold value on the x-axis.
yZoneColor	Layer	Create a y-zone color. A y-zone will change from one color to another depending on a threshold value on the y-axis.
setDataLabelStyle	Layer	Enable data labels and set their styles.
setDataLabelFormat	Layer	Set the data label format.
addCustomDataLabel	Layer	Add a custom data label to a data point.
setAggregateLabelStyle	Layer	Enable aggregate labels and set their styles.
setAggregateLabelFormat	Layer	Set the aggregate label format.
addCustomAggregateLabel	Layer	Add a custom aggregate label to an aggregated object.
getImageCoor	Layer	Get the image map coordinates of a data point as represented in the layer as HTML image map attributes.
getImageCoor2	Layer	Get the image map coordinates of a region containing all data points at the given x-position as HTML image map attributes.
getHTMLImageMap	Layer	Generate the HTML image map for all data points as represented on the layer.
setHTMLImageMap	Layer	Override the default arguments used when generating HTML image map for the layer.