Nearest point to a given x value

JayG · Post by **JayG** » Thu Mar 29, 2007 9:29 pm

Is there a way (other than looping through the points) to find the index of the point nearest a given X-axis value?

For example, the X-axis minimum value is 20 and the X-axis maximum value is 50, and I want to know which point in TChart1.Series(0) has an X-value closest to 23?

Jay

Narcís · Post by **Narcís** » Fri Mar 30, 2007 10:39 am

Hi JayG,

At the moment I can think of 2 ways to achieve what you request:

1. Using NearestPoint tool to see the neares point to your mouse position in the chart.
2. Using an invisible CursorTool and its methods to calculate nearest point.

At the code snippet below you'll find an example of both options:

Code: Select all

		public Form1()
		{
			InitializeComponent();
			InitializeChart();
		}

		private void InitializeChart()
		{
			tChart1.Aspect.View3D = false;

			points1 = new Steema.TeeChart.Styles.Points(tChart1.Chart);
			points1.FillSampleValues();

			nearesPoint1 = new Steema.TeeChart.Tools.NearestPoint(tChart1.Chart);
			nearesPoint1.Series = points1;

			cursorTool1 = new Steema.TeeChart.Tools.CursorTool(tChart1.Chart);
			cursorTool1.Active = false;
			cursorTool1.Style = Steema.TeeChart.Tools.CursorToolStyles.Vertical;
			cursorTool1.Series = points1;
			cursorTool1.Snap = true;
		}

		private void button1_Click(object sender, EventArgs e)
		{
			cursorTool1.XValue = Convert.ToDouble(textBox1.Text);
			cursorTool1.SnapToPoint();
			label1.Text = cursorTool1.XValue.ToString();
		}

JayG · Post by **JayG** » Fri Mar 30, 2007 2:26 pm

The problem with those methods is that they rely on the mouse cursor. I want to find the point based on some variables independant of where the mouse is.

Jay

Narcís · Post by **Narcís** » Fri Mar 30, 2007 2:45 pm

Hi JayG,

Sorry but I'm afraid can't do anything else on that if you don't want to use mentioned features nor looping through series' ValueLists.

Since, by default, XValues ValueList is sorted in ascending order, the only solution I can think of is using any of the widely known search algorithms that don't loop through an entire array (ValueList in that case). You should find information about that kind of algorithms in internet.

JayG · Post by **JayG** » Fri Mar 30, 2007 3:56 pm

Narcís,

Thanks, I thought that might be the case, but I didn't want to spend time to include a search algorithm if there was already a TChart method that did the same thing.

Jay

jenb · Post by **jenb** » Thu Dec 13, 2007 2:30 pm

Hi

I am trying to do find the nearest series x value to a mouse clicked point and am basing my code on your example. as shown below:

Code: Select all

foreach (Steema.TeeChart.Styles.Series ts in _tcChart.Series)
                {
                    if (ts is Steema.TeeChart.Styles.Line)
                    {
                        _tlCursor.Series = ts;
                        double dX = ts.XScreenToValue(e.X);
                        _tlCursor.XValue = dX;
                        _tlCursor.SnapToPoint();
                        strLabel += string.Format("X = {0}", _tlCursor.XValue.ToString("0.##"));
                    }
                }

The series has 2048 values (integers 0 to 2047). The first time this function is performed the _tlCursor.XValue always goes to 1022 although dX is not 1022, and the label displays "X = 1022". If the function is performed again then the correct version of X is shown.

Any suggestions?

Narcís · Post by **Narcís** » Thu Dec 13, 2007 3:24 pm

Hi jenb,

Why don't you try using a NearestPoint tool and retrieve its Point property in the desired mouse event?

jenb · Post by **jenb** » Thu Dec 13, 2007 3:31 pm

Hi Narcis

I am using the Nearest point tool for another case but in this case I want to find the nearest point in the x direction only (i.e. in a horizontal line from the clicked point to intersect with the series line), as far as I know the nearest point tool uses the shortest line to the series, and of course this line generally isn't horizontal.

Anyway your example using the cursor tool is exactly what I want, there's just a problem when it runs the first time.

Thanks

jenb

Narcís · Post by **Narcís** » Thu Dec 13, 2007 3:38 pm

Hi jenb,

Anyway your example using the cursor tool is exactly what I want, there's just a problem when it runs the first time.

Which example do you mean? Which is the exact problem with it? Maybe forcing the chart being internally repainted after its initalizations solves this issue:

Code: Select all

Bitmap bmp = tChart1.Bitmap;

jenb · Post by **jenb** » Thu Dec 13, 2007 3:55 pm

Which example do you mean?

The example is as shown here:

public Form1()
{
InitializeComponent();
InitializeChart();
}

private void InitializeChart()
{
tChart1.Aspect.View3D = false;

points1 = new Steema.TeeChart.Styles.Points(tChart1.Chart);
points1.FillSampleValues();

nearesPoint1 = new Steema.TeeChart.Tools.NearestPoint(tChart1.Chart);
nearesPoint1.Series = points1;

cursorTool1 = new Steema.TeeChart.Tools.CursorTool(tChart1.Chart);
cursorTool1.Active = false;
cursorTool1.Style = Steema.TeeChart.Tools.CursorToolStyles.Vertical;
cursorTool1.Series = points1;
cursorTool1.Snap = true;
}

private void button1_Click(object sender, EventArgs e)
{
cursorTool1.XValue = Convert.ToDouble(textBox1.Text);
cursorTool1.SnapToPoint();
label1.Text = cursorTool1.XValue.ToString();
}

The problem is this:

I am trying to do find the nearest series x value to a mouse clicked point and am basing my code on your example. as shown below:

Code:
foreach (Steema.TeeChart.Styles.Series ts in _tcChart.Series)
{
if (ts is Steema.TeeChart.Styles.Line)
{
_tlCursor.Series = ts;
double dX = ts.XScreenToValue(e.X);
_tlCursor.XValue = dX;
_tlCursor.SnapToPoint();
strLabel += string.Format("X = {0}", _tlCursor.XValue.ToString("0.##"));
}
}

The series has 2048 values (integers 0 to 2047). The first time this function is performed the _tlCursor.XValue always goes to 1022 although dX is not 1022, and the label displays "X = 1022". If the function is performed again then the correct version of X is shown.

I added Bitmap bmp = _tcChart.Bitmap before the call to set _tlCursor.XValue - it made no difference.

Narcís · Post by **Narcís** » Fri Dec 14, 2007 9:02 am

Hi jenb,

Thanks for the information.

This seems a bug to me and I've added it (TF02012649) to our defect list to be fixed for future releases. In the meantime, a workaround is calling the cursor setting code twice the first time, for example:

Code: Select all

		public Form1()
		{
			InitializeComponent(); 
			InitializeChart();
		}

		private Steema.TeeChart.Styles.Line line1;
		private Steema.TeeChart.Tools.CursorTool cursorTool1;
		private bool firstTime;

		private void InitializeChart()
		{
			tChart1.Clear();
			tChart1.Aspect.View3D = false;

			line1 = new Steema.TeeChart.Styles.Line(tChart1.Chart);
			line1.FillSampleValues();

			cursorTool1 = new Steema.TeeChart.Tools.CursorTool(tChart1.Chart);
			cursorTool1.Active = false;
			cursorTool1.Style = Steema.TeeChart.Tools.CursorToolStyles.Vertical;
			cursorTool1.Series = line1;
			cursorTool1.Snap = true;

			firstTime = true;
		}		

		private void tChart1_MouseClick(object sender, MouseEventArgs e)
		{
			foreach (Steema.TeeChart.Styles.Series ts in tChart1.Series)
			{
				if (ts is Steema.TeeChart.Styles.Line)
				{
					cursorTool1.Series = ts;
					double dX;

					dX = SetCursor(e.X, ts);

					//Workaround
					if (firstTime)
					{
						dX = SetCursor(e.X, ts);
						firstTime = false;
					}
					
					label1.Text = string.Format("X = {0}", cursorTool1.XValue.ToString("0.##"));
				}
			} 
		}

		private double SetCursor(int X, Steema.TeeChart.Styles.Series ts)
		{
			double dX;
			dX = ts.XScreenToValue(X);
			cursorTool1.XValue = dX;
			cursorTool1.SnapToPoint();
			return dX;
		}

		private void button1_Click(object sender, EventArgs e)
		{
			InitializeChart();
		}