This coded is useful is you have to draw a velocity field in a two dimensional mesh

This procedure draw vectors on a Chart component.


procedure TDatosInput.Vector(VArrayX,VArrayY: TArray2D; VArrayU,VArrayV: TArray3D; nx,ny,nt: DWord; Malla: TPointSeries; Chrt: TChart; ColorVector: TColor; Fact: DWord);
var
i,j,PosX: DWord;
xi,yi,xf,yf: Longint;
Xn,Yn: Extended;
Dx,Dy: Extended;
Ang: Extended;
begin

  {Config Canvas}
  Chrt.Canvas.Pen.Color:=ColorVector;
  Chrt.Canvas.Brush.Color:=ColorVector;

  {Paint Color at each cell}
  for j:=0 to ny-1 do
  for i:=0 to nx-1 do
  begin

    {Calc Angle}
    PosX:=i;
    if (i = nx-1) then PosX:=nx-2;
    Dx:=VArrayX[PosX+1,j]-VArrayX[PosX,j];
    Dy:=VArrayY[PosX+1,j]-VArrayY[PosX,j];

    {Check Dx}
    Ang:=0;
    if (Dx = 0) or (Dy = 0) then
      begin
        if (Dy > 0) and (Dx = 0) then Ang:=0.5*Pi;
        if (Dy < 0) and (Dx = 0) then Ang:=1.5*Pi;
        if (Dy = 0) and (Dx > 0) then Ang:=0;
        if (Dy = 0) and (Dx < 0) then Ang:=Pi;
      end
    else
      begin
        Ang:=ArcTan(Dy/Dx);
        {Check Position}
        if ((Dy > 0) or (Dy < 0)) and (Dx < 0) then
          Ang:=Ang+Pi;
      end;

    {New Coordinates - Rotating the Vector}
    xn:=VArrayU[i,j,nt]*Fact*Cos(Ang)-VArrayV[i,j,nt]*Fact*Sin(Ang);
    yn:=VArrayU[i,j,nt]*Fact*Sin(Ang)+VArrayV[i,j,nt]*Fact*Cos(Ang);

    {Drawing the Arrow}
    xi:=Malla.CalcXPosValue(VArrayX[i,j]);
    yi:=Malla.CalcYPosValue(VArrayY[i,j]);
    xf:=Malla.CalcXPosValue(xn+VArrayX[i,j]);
    yf:=Malla.CalcYPosValue(yn+VArrayY[i,j]);
    Chrt.Canvas.Arrow(False,Point(xi,yi),Point(xf,yf),5,10,0);
  end;

end;