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POCore Plot - How to convert touch point to plot point in a plot space with log axis
 

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  1. POCore Plot - How to convert touch point to plot point in a plot space with log axis
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    <p>I have a scatter plot with a linear y axis and logarithmic x axis, all of which works great. But when I try to convert a touch point into the plot space coordinates, I'm having problems.</p> <p>I have seen something like the following suggested various places:</p> <pre><code>- (BOOL)plotSpace:(CPTPlotSpace *)space shouldHandlePointingDeviceUpEvent:(id)event atPoint:(CGPoint)point { CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)space; CPTScatterPlot *scatterPlot = [[[plotSpace graph] allPlots] objectAtIndex:0]; CGPoint plotAreaPoint = [[plotSpace graph] convertPoint:point toLayer:scatterPlot]; NSLog(@"PlotAreaPoint : %.1f, %.1f", plotAreaPoint.x, plotAreaPoint.y); NSDecimal dataPoint[2]; NSDecimalNumber *xCoordinate, *yCoordinate; [plotSpace plotPoint:dataPoint forPlotAreaViewPoint:plotAreaPoint]; xCoordinate = [NSDecimalNumber decimalNumberWithDecimal:dataPoint[0]]; yCoordinate = [NSDecimalNumber decimalNumberWithDecimal:dataPoint[1]]; NSLog(@"DataPoint : %.1f, %.1f", [xCoordinate floatValue], [yCoordinate floatValue]); return YES; } </code></pre> <p>When I run this, plotAreaPoint seems correct, and yCoordinate is correct. xCoordinate is correct if I tap at the left edge (5.0) or right edge (500.0), but behaves like a linear axis if I tap in the middle. If I tap in the very middle, I get 250.0 or so, instead of 50.0. Am I missing something, or is there another way to do this?</p> <p>Thanks, Tim</p>
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