How to create a real smooth curve?

[UliBru]

Hi,

I have the following simple code based on a chart with two line series:

Code: Select all

procedure TForm1.FormCreate(Sender: TObject);
begin
  Chart1.BottomAxis.Logarithmic := true;
  Chart1.BottomAxis.Automatic := false;
  Chart1.BottomAxis.Maximum := 10000;
  Chart1.BottomAxis.Minimum := 10;
  Chart1.LeftAxis.Maximum := 6;
  Chart1.LeftAxis.Minimum := -6;
  Series1.Pointer.Visible := true;
  Series2.DataSource := Series1;
  Series2.Color := clRed;
  Series1.Clear;
  Series1.AddXY(10,2,'',clTeeColor);
  Series1.AddXY(32,2,'',clTeeColor);
  Series1.AddXY(600,2.5,'',clTeeColor);
  Series1.AddXY(1000,0,'',clTeeColor);
  Series1.AddXY(2000,-2,'',clTeeColor);
  Series1.AddXY(8000,-1.5,'',clTeeColor);
  Series1.AddXY(10000,-1.5,'',clTeeColor);
  Series2.CheckDataSource;
  Series2.Smoothed := true;
end;

The target is to get a smooth Series2 through the data points given by Series1.

But it does not look smooth at all:

Smoothing.PNG (14.12 KiB) Viewed 11010 times

Without interpolation the curve is smooth but is does not go thru the points.

How to fix it?

BR
Uli

PS: using TSmoothingFunction leads to the same result

[Yeray]

Hello,

I see there's a problem in the TSmoothingFunction. I've added it to the public tracker:
http://bugs.teechart.net/show_bug.cgi?id=1890

As you can see, I can think on two workarounds:
- To use THorizLineSeries instead of TLineSeries.
- To use this code:

Code: Select all

  Series2.XValues.Order:=loNone;
  Series2.HasZValues:=True;

[UliBru]

Hello Yeray,

THorizLineSeries seems not to work properly.

Code: Select all

  Series2.XValues.Order:=loNone;
  Series2.HasZValues:=True;

seems to work.

But adding e.g. another point by

Code: Select all

  Series1.AddXY(1300,-1.2,'',clTeeColor);

between X=1000 and X=2000 (is ascending X sequence) creates a picture like

Smoothing2.PNG (14.04 KiB) Viewed 11000 times

So the smoothing seems to have some tendency for oscillations.

BR
Uli

[Yeray]

Hello Uli,

THorizLineSeries seems not to work properly.

This is what I get with TeeChart v2017.22 and the code below:

Project2_2017-07-12_08-24-01.png (13.76 KiB) Viewed 10996 times

Code: Select all

uses Series;

var Series1, Series2: THorizLineSeries;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Chart1.View3D:=False;

  Series1:=Chart1.AddSeries(THorizLineSeries) as THorizLineSeries;
  Series2:=Chart1.AddSeries(THorizLineSeries) as THorizLineSeries;

  Chart1.Axes.Bottom.Logarithmic := true;
  Chart1.Axes.Bottom.SetMinMax(10, 10000);
  Chart1.Axes.Left.SetMinMax(-6, 6);

  Series1.Pointer.Visible := true;
  Series2.DataSource := Series1;
  Series2.Color := clRed;
  Series1.Clear;

  Series1.AddXY(10,2,'',clTeeColor);
  Series1.AddXY(32,2,'',clTeeColor);
  Series1.AddXY(600,2.5,'',clTeeColor);
  Series1.AddXY(1000,0,'',clTeeColor);
  Series1.AddXY(2000,-2,'',clTeeColor);
  Series1.AddXY(8000,-1.5,'',clTeeColor);
  Series1.AddXY(10000,-1.5,'',clTeeColor);

  Series2.CheckDataSource;
  Series2.Smoothed := true;
end;

Code: Select all

  Series2.XValues.Order:=loNone;
  Series2.HasZValues:=True;

seems to work.

But adding e.g. another point by

Code: Select all

  Series1.AddXY(1300,-1.2,'',clTeeColor);

between X=1000 and X=2000 (is ascending X sequence) creates a picture like

So the smoothing seems to have some tendency for oscillations.

I'm not sure why this is happening but it seems the BSpline is giving a different result when using those series values and when transforming those values to screen pixels.
You can use the TBSpline as follows to use pixel values, transform the result back to axis values to add them into Series2:

Project2_2017-07-12_10-33-47.png (13.94 KiB) Viewed 10996 times

Code: Select all

uses Series, TeeSpLine;

var Series1, Series2: TLineSeries;

procedure TForm1.FormCreate(Sender: TObject);
var BSpline : TBSpline;
    i: Integer;
    ParameterValue : single;
    V       : TVertex;
begin
  Chart1.View3D:=False;

  Series1:=Chart1.AddSeries(TLineSeries) as TLineSeries;
  Series2:=Chart1.AddSeries(TLineSeries) as TLineSeries;

  Chart1.Axes.Bottom.Logarithmic := true;
  Chart1.Axes.Bottom.SetMinMax(10, 10000);
  Chart1.Axes.Left.SetMinMax(-6, 6);

  Series1.Pointer.Visible := true;

  Series1.AddXY(10,2,'',clTeeColor);
  Series1.AddXY(32,2,'',clTeeColor);
  Series1.AddXY(600,2.5,'',clTeeColor);
  Series1.AddXY(1000,0,'',clTeeColor);
  Series1.AddXY(1300,-1.2,'',clTeeColor);
  Series1.AddXY(2000,-2,'',clTeeColor);
  Series1.AddXY(8000,-1.5,'',clTeeColor);
  Series1.AddXY(10000,-1.5,'',clTeeColor);

  Chart1.Draw;

  BSpline:=TBSpline.Create;

  for i:=0 to Series1.Count-1 do
    BSpline.AddPoint(Series1.CalcXPos(i), Series1.CalcYPos(i));

  BSpline.Interpolated:=True;
  BSpline.Fragments:=64;

  Series2.Color:=clRed;
  Series2.XValues.Order:=loNone;

  For i:=0 to BSpline.Fragments do
  begin
    ParameterValue:=(i/BSpline.Fragments);
    V:=BSpline.Value(ParameterValue);

    with Series2 do
      AddXY(GetHorizAxis.CalcPosPoint(Round(V.X)),GetVertAxis.CalcPosPoint(Round(V.Y)));
  end;
end;;

[UliBru]

Hello Yeray,

many thanks.

- Uli

[Yeray]

Hello Uli,

Note I've just edited my last post to calculate the spline at OnCreate and use the output in Series2 instead of having to recalculate it at every repaint at OnAfterDraw event.