How to find intersection point between a lineseries and a vertical line.

Question

I have a lineseries chart (refer the screenshot). As I move the spend slider shown in the attachment, a vertical line is drawn in the chart. (I did this using the cartesian canvas as annotation element - using canvas.moveTo(), canvas.lineTo() functions)
I want to find out the intersection point(y value) where the vertical line meets the lineseries. Can someone help me on this. It will be really helpful.
Thanks,
Jayakrishnan

Answer 1

Here are a few functions I wrote years ago for common chart transformations... the function you're going to focus on for your solution is chartToScreen...
*  Converts the screen position to chart value position
*  @param thePos - Number - The position you want to convert
*  @private
        private function getChartCoordinates(thePos:Point):Object
               var tmpArray:Array = dataTransform.invertTransform(thePos.x, thePos.y);
               return {x:tmpArray[0], y:tmpArray[1]};
*  Takes a non-numeric chart value and returns a proper numeric value
*  @param inValue - String - The display name of the instance showing on the axis (eg. if we're showing months, it might be 'Sep - 06'
*  @param theAxis - IAxis - The axis on which we're looking
          public function getNumericChartValue(inValue:String, theAxis:IAxis):Object
               var axisCache:Array = new Array({inValue: inValue})                 
               if(!(theAxis is LinearAxis))
                    theAxis.mapCache(axisCache, "inValue", "outValue", true);
                    return {numericValue: axisCache[0].outValue}
               else
                    return {numericValue: Number(inValue)};
*  Converts the chart values into screen coordinate values
*  @param chartX - Number - The display name of the instance showing on the axis (eg. if we're showing months, it might be 'Sep - 06'
*  @param chartY - Number - The axis on which we're looking
          public function chartToScreen(chartX:Number, chartY:Number, theSeries:Series):Point
               var tmpCache:Array = new Array({chartX:chartX, chartY:chartY});
               if(theSeries)
                    theSeries.dataTransform.transformCache(tmpCache, "chartX", "screenX", "chartY", "screenY");
               else
                    dataTransform.transformCache(tmpCache, "chartX", "screenX", "chartY", "screenY");
               return new Point(Math.round(tmpCache[0].screenX), Math.round(tmpCache[0].screenY));
*  takes a point in mouse position, and runs it through converting to chart coordinates, converts chart coordinate to numeric value if needed
*  and then back into mouse position to get the nearest axis snap point
*  @param thePoint - Point - The position we're converting
*  @private
          private function getSnapPosition(thePoint:Point):Point
               var chartPoint:Object = getChartCoordinates(new Point(thePoint.x, thePoint.y));
               //if either of the axis chart results is not in numeric format, we get the numeric equivalent of it
               var chartX:* = chartPoint.x;
               var chartY:* = chartPoint.y;
               chartX = getNumericChartValue(chartPoint.x, CartesianChart(this.chart).horizontalAxis).numericValue;
               chartY = getNumericChartValue(chartPoint.y, CartesianChart(this.chart).verticalAxis).numericValue;
               return chartToScreen(chartX, chartY, null);