jFreeChart contour plot rendering incorrectly - scala

Question

Code:
package vu.co.kaiyin.sfreechart.plots
import java.awt.{Shape, Stroke, RenderingHints}
import javax.swing.JFrame
import org.jfree.chart.plot.{PlotOrientation, XYPlot}
import org.jfree.chart.{ChartFactory => cf}
import org.jfree.chart.renderer.GrayPaintScale
import org.jfree.chart.renderer.xy.XYBlockRenderer
import org.jfree.chart.title.PaintScaleLegend
import org.jfree.chart._
import org.jfree.chart.axis.{AxisLocation, NumberAxis}
import org.jfree.data.Range
import org.jfree.data.general.DatasetUtilities
import org.jfree.data.statistics.HistogramDataset
import org.jfree.data.xy.{IntervalXYDataset, XYZDataset}
import org.jfree.ui.{RectangleEdge, RectangleInsets}
import vu.co.kaiyin.sfreechart.{ColorPaintScale, ExtendedFastScatterPlot}
import vu.co.kaiyin.sfreechart.implicits._
import scala.util.Random.nextGaussian
/**
* Created by kaiyin on 2/10/16.
*/
object Plots {
def histogram(
dataset: IntervalXYDataset,
title: String = "Histogram",
xAxisLabel: String = "Intervals",
yAxisLabel: String = "Count",
orientation: PlotOrientation = PlotOrientation.VERTICAL,
legend: Boolean = true,
tooltips: Boolean = true,
urls: Boolean = true,
alpha: Float = 0.5F,
pannable: Boolean = false
): JFreeChart = {
val hist = cf.createHistogram(
title, xAxisLabel, yAxisLabel, dataset, orientation, legend, tooltips, urls
)
val xyPlot = hist.getPlot.asInstanceOf[XYPlot]
if (pannable) {
xyPlot.setDomainPannable(true)
xyPlot.setRangePannable(true)
}
xyPlot.setForegroundAlpha(alpha)
hist
}
def controuPlot(dataset: XYZDataset, title: String = "Contour plot", scaleTitle: String = "Scale"): JFreeChart = {
val xAxis = new NumberAxis("x")
val yAxis = new NumberAxis("y")
val blockRenderer = new XYBlockRenderer
val zBounds: Range = DatasetUtilities.findZBounds(dataset)
println(zBounds.getLowerBound, zBounds.getUpperBound)
val paintScale = new ColorPaintScale(zBounds.getLowerBound, zBounds.getUpperBound)
blockRenderer.setPaintScale(paintScale)
val xyPlot = new XYPlot(dataset, xAxis, yAxis, blockRenderer)
xyPlot.setAxisOffset(new RectangleInsets(1D, 1D, 1D, 1D))
xyPlot.setDomainPannable(true)
xyPlot.setRangePannable(true)
val chart = new JFreeChart(title, xyPlot)
chart.removeLegend()
val scaleAxis = new NumberAxis(scaleTitle)
val paintScaleLegend = new PaintScaleLegend(paintScale, scaleAxis)
paintScaleLegend.setAxisLocation(AxisLocation.BOTTOM_OR_LEFT)
paintScaleLegend.setPosition(RectangleEdge.BOTTOM)
chart.addSubtitle(paintScaleLegend)
chart
}
def fastScatter(data: Array[Array[Float]], title: String = "Scatter plot", pointSize: Int = 5, pointAlpha: Float = 0.3F): JFreeChart = {
val xAxis = new NumberAxis("x")
val yAxis = new NumberAxis("y")
xAxis.setAutoRangeIncludesZero(false)
yAxis.setAutoRangeIncludesZero(false)
val fsPlot = new ExtendedFastScatterPlot(data, xAxis, yAxis, pointSize, pointAlpha)
fsPlot.setDomainPannable(true)
fsPlot.setRangePannable(true)
val chart = new JFreeChart(title, fsPlot)
chart.getRenderingHints.put(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON)
chart
}
def main(args: Array[String]) {
// fastScatter(Array(Array(1.0F, 2.0F, 3.0F), Array(1.0F, 2.0F, 3.0F))).vis()
val x = (1 to 10000).map(_.toFloat).toArray
val y = x.map(i => i * nextGaussian().toFloat * 3F).toArray
fastScatter(Array(x, y)).vis()
val x1 = (-13.0 to 13.0 by 0.2).toArray
val y1 = (-13.0 to 13.0 by 0.2).toArray
val xyzData = (for {
i <- x1
j <- y1
if i > j
} yield Array(i, j, math.sin(i) + math.cos(j))).transpose
controuPlot(xyzData.toXYZDataset()).vis()
histogram((1 to 10000).map(_ => nextGaussian()).toArray.toHistogramDataset()).vis()
}
}
Full project can be found here: https://github.com/kindlychung/sfreechart
Running the above code will give you this:
If you look carefully, you will find a narrow band of pixels along the diagonal edge that doesn't quite fit (this is a contour plot of sin(x) + cos(y)), as if there was a tear and shift. But if I comment out the if i < j line, then the plot looks normal:
What went wrong and how can this be solved?
Update
Actually, if you look carefully at the right edge of the second figure above, there is also a strip that shouldn't be there.

Answer 1

I managed to fake a contour plot by a scatter plot:
val x = (-12.0 to 12.0 by 0.1).toArray
val y = (-12.0 to 12.0 by 0.1).toArray
val xyzData = (for {
i <- x
j <- y
} yield {
val s = math.sin(i)
val c = math.cos(j)
Array(i, j, s + c)
}).transpose
fastScatter(xyzData.toFloats, grid = (false, false), pointSize = 4, pointAlpha = 1F).vis()
Implementation of fastScatter can be found here: https://github.com/kindlychung/sfreechart (disclosure: I am the author.)