Steema Central

Posted: **Thu Sep 16, 2004 6:12 pm**

Does anyone have an algorithm to plot a circle about a non centered point using a TPolarSeries?

Posted: **Fri Sep 17, 2004 2:34 pm**

Hi.

All you have to do is transform values from local coordinate system to global angle,radius. The following code should explain what I meant:

Code: Select all

// angles measured in radians
procedure TransformCoord(const r0,a0: double; var angle, radius: double);
var x,y: double;
begin
  x := r0*cos(a0) + radius*cos(angle);
  y := r0*cos(a0) + radius*sin(angle);
  radius := Sqrt(Sqr(x)+Sqr(y));
  angle := ArcTan2(y,x);
end;

procedure TForm1.FormCreate(Sender: TObject);
var t: Integer;
    r,a: Double;
begin
  Series1.GetVertAxis.SetMinMax(0,200);
  Series1.XValues.Order := loNone;
  // draw circle with radius 25 at r0=100, angle = 2*Pi/3
  for t:= 1 to 20 do
  begin
    // local coordinates
    r := 25;
    a := 2*Pi*t/20.0;
    // transform to global coords
    TransformCoord(100,2*Pi/3.0,a,r);
    // angle to degrees
    a := a* 180.0/Pi;
    Series1.AddPolar(a,r);
  end;
end;

Alternatively, if you only want to draw circle, not related to series points at specific coordinates, all you have to do is manually draw using TChart.Canvas.Circle method in TChart OnAfterDraw event.