Questions about scatter plot in Core Plot

Question

I am making a scatter plot app in Core Plot 1.4. I am new to Objective-C and Core Plot, so sorry for asking some basic questions. Here is some code I wrote by imitating the sample program(CPTTestApp-iphone).

- (void)viewDidLoad
{
    [super viewDidLoad];

    ...

    // Add some initial data
    NSMutableArray *contentArray = [NSMutableArray arrayWithCapacity:100];
    int i;
    for ( i = 0; i < 60; i++ ) {
        id x = [NSNumber numberWithFloat:1 + i * 0.05];
        id y = [NSNumber numberWithInt:1]; //[NSNumber numberWithFloat:1.2 * rand() / (float)RAND_MAX + 1.2];
        [contentArray addObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:x, @"x", y, @"y", nil]];
    }
    dataForPlot = contentArray;


    // Create graph from theme
    graph = [[CPTXYGraph alloc] initWithFrame:CGRectZero];
    CPTTheme *theme = [CPTTheme themeNamed:kCPTDarkGradientTheme];
    [graph applyTheme:theme];
    CPTGraphHostingView *hostingView = [[CPTGraphHostingView alloc] init]; 
    hostingView.collapsesLayers = NO; // Setting to YES reduces GPU memory usage, but can slow drawing/scrolling
    hostingView.hostedGraph     = graph;
    [self setView:hostingView];

    graph.paddingLeft   = 0.0;
    graph.paddingTop    = 0.0;
    graph.paddingRight  = 0.0;
    graph.paddingBottom = 30.0;

    // Setup plot space
    CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)graph.defaultPlotSpace;
    plotSpace.allowsUserInteraction = YES;

    [plotSpace setXRange:[CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(0) length:CPTDecimalFromInteger(5)]];
    [plotSpace setYRange:[CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(0) length:CPTDecimalFromInteger(7)]];


    // Axes
    CPTXYAxisSet *axisSet = (CPTXYAxisSet *)graph.axisSet;
    CPTXYAxis *x          = axisSet.xAxis;
    x.majorIntervalLength         = CPTDecimalFromString(@"1");
    x.orthogonalCoordinateDecimal = CPTDecimalFromString(@"0");
    x.minorTicksPerInterval       = 5;
    NSArray *exclusionRanges = [NSArray arrayWithObjects:
                                [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(1.99) length:CPTDecimalFromFloat(0.02)],
                                [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.99) length:CPTDecimalFromFloat(0.02)],
                                [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(2.99) length:CPTDecimalFromFloat(0.02)],
                                nil];
    x.labelExclusionRanges = exclusionRanges;

    CPTXYAxis *y = axisSet.yAxis;
    y.majorIntervalLength         = CPTDecimalFromString(@"1");
    y.minorTicksPerInterval       = 5;
    y.orthogonalCoordinateDecimal = CPTDecimalFromString(@"0");
    exclusionRanges               = [NSArray arrayWithObjects:
                                     [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(1.99) length:CPTDecimalFromFloat(0.02)],
                                     [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(0.99) length:CPTDecimalFromFloat(0.02)],
                                     [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(3.99) length:CPTDecimalFromFloat(0.02)],
                                     nil];
    y.labelExclusionRanges = exclusionRanges;
    y.delegate             = self;


    // Create a blue plot area
    CPTScatterPlot *boundLinePlot  = [[CPTScatterPlot alloc] init];
    CPTMutableLineStyle *lineStyle = [CPTMutableLineStyle lineStyle];
    lineStyle.miterLimit        = 1.0f;
    lineStyle.lineWidth         = 3.0f;
    lineStyle.lineColor         = [CPTColor blueColor];
    boundLinePlot.dataLineStyle = lineStyle;
    boundLinePlot.identifier    = @"Blue Plot";
    boundLinePlot.dataSource    = self;

    [graph addPlot:boundLinePlot toPlotSpace:plotSpace];

    // Do a blue gradient
    CPTColor *areaColor1       = [CPTColor colorWithComponentRed:0.3 green:0.3 blue:1.0 alpha:0.8];
    CPTGradient *areaGradient1 = [CPTGradient gradientWithBeginningColor:areaColor1 endingColor:[CPTColor clearColor]];
    areaGradient1.angle = -90.0f;
    CPTFill *areaGradientFill = [CPTFill fillWithGradient:areaGradient1];
    boundLinePlot.areaFill      = areaGradientFill;
    boundLinePlot.areaBaseValue = [[NSDecimalNumber zero] decimalValue];

    // interpolation
    boundLinePlot.interpolation = CPTScatterPlotInterpolationCurved;

#ifdef PERFORMANCE_TEST
[NSTimer scheduledTimerWithTimeInterval:2.0 target:self  selector:@selector(changePlotRange) userInfo:nil repeats:YES];
#endif
}

Now I have some questions.

1. From dataForPlot, a blue line with gradient must be rendered the height y=1, but after running this it was not shown. (I haven't adjust the range of x values in dataForPlot but a partial line should be rendered.)

2. How can I move the origin (0,0) to the middle of the screen?

3. Why do 1.0-3.0 in x-axis and 1.0, 2.0, 4.0 in y-axis disappear?

Can anyone help me figure these out? Thank you.

Answer 1

1. What data is being plotted? Please show the datasource methods.

2. The visible data ranges in the plot area are controlled by the plot space:

   plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(-5)
                                                   length:CPTDecimalFromInteger(10)];
   plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromInteger(-7) 
                                                   length:CPTDecimalFromInteger(14)];
   

3. The labelExclusionRanges skips over any labels in the specified ranges. If you want to see all of the ticks and labels, don't set this property.