Contour Interpolation

This example demonstrates spline and linear surface interpolation, and discrete and continuous coloring for the ContourLayer.

The input to the contour layer are the z values at certain (x, y) points. To draw the contour and to color the layer, it is necessarily to know the z values at all pixels in the xy plane. ChartDirector uses surface interpolation to compute the z values at all pixels from the given data points. Two types of interpolation - spline and linear - are supported. They can be configured using ContourLayer.setSmoothInterpolation.

The coloring of the contour layer can be discrete or continuous, configurable using ColorAxis.setColorGradient or ColorAxis.setColorScale.

[JSP Version] jspdemo/contourinterpolate.jsp

<%@page import="ChartDirector.*, java.util.*" %>
<%!
// Function to create the demo charts
void createChart(WebChartViewer viewer, int chartIndex)
{
    // The x and y coordinates of the grid
    double[] dataX = {-4, -3, -2, -1, 0, 1, 2, 3, 4};
    double[] dataY = {-4, -3, -2, -1, 0, 1, 2, 3, 4};

    // The values at the grid points. In this example, we will compute the values using the formula
    // z = Sin(x * pi / 3) * Sin(y * pi / 3).
    double[] dataZ = new double[dataX.length * dataY.length];
    for(int yIndex = 0; yIndex < dataY.length; ++yIndex) {
        double y = dataY[yIndex];
        for(int xIndex = 0; xIndex < dataX.length; ++xIndex) {
            double x = dataX[xIndex];
            dataZ[yIndex * dataX.length + xIndex] = Math.sin(x * 3.1416 / 3) * Math.sin(y * 3.1416 /
                3);
        }
    }

    // Create a XYChart object of size 360 x 360 pixels
    XYChart c = new XYChart(360, 360);

    // Set the plotarea at (30, 25) and of size 300 x 300 pixels. Use semi-transparent black
    // (c0000000) for both horizontal and vertical grid lines
    c.setPlotArea(30, 25, 300, 300, -1, -1, -1, 0xc0000000, -1);

    // Add a contour layer using the given data
    ContourLayer layer = c.addContourLayer(dataX, dataY, dataZ);

    // Set the x-axis and y-axis scale
    c.xAxis().setLinearScale(-4, 4, 1);
    c.yAxis().setLinearScale(-4, 4, 1);

    if (chartIndex == 0) {
        // Discrete coloring, spline surface interpolation
        c.addTitle("Spline Surface - Discrete Coloring", "Arial Bold Italic", 12);
    } else if (chartIndex == 1) {
        // Discrete coloring, linear surface interpolation
        c.addTitle("Linear Surface - Discrete Coloring", "Arial Bold Italic", 12);
        layer.setSmoothInterpolation(false);
    } else if (chartIndex == 2) {
        // Smooth coloring, spline surface interpolation
        c.addTitle("Spline Surface - Continuous Coloring", "Arial Bold Italic", 12);
        layer.setContourColor(Chart.Transparent);
        layer.colorAxis().setColorGradient(true);
    } else {
        // Discrete coloring, linear surface interpolation
        c.addTitle("Linear Surface - Continuous Coloring", "Arial Bold Italic", 12);
        layer.setSmoothInterpolation(false);
        layer.setContourColor(Chart.Transparent);
        layer.colorAxis().setColorGradient(true);
    }

    // Output the chart
    viewer.setChart(c, Chart.SVG);
}
%>
<%
// This example includes 4 charts
WebChartViewer[] viewers = new WebChartViewer[4];
for (int i = 0; i < viewers.length; ++i) {
    viewers[i] = new WebChartViewer(request, "chart" + i);
    createChart(viewers[i], i);
}
%>
<!DOCTYPE html>
<html>
<head>
    <title>Contour Interpolation</title>
    <!-- Include ChartDirector Javascript Library to support chart interactions -->
    <script type="text/javascript" src="cdjcv.js"></script>
</head>
<body style="margin:5px 0px 0px 5px">
    <div style="font:bold 18pt verdana;">
        Contour Interpolation
    </div>
    <hr style="border:solid 1px #000080; background:#000080" />
    <div style="font:10pt verdana; margin-bottom:1.5em">
        <a href="viewsource.jsp?file=<%=request.getServletPath()%>">View Source Code</a>
    </div>
    <!-- ****** Here are the chart images ****** -->
    <%
        for (int i = 0; i < viewers.length; ++i) {
            out.write(viewers[i].renderHTML(response));
            out.write(" ");
        }
    %>
</body>
</html>