Countour plot based on velocity data

I have data consist of X(x coordinate) Y(y coordinate) Z(velocity). I created below countour plot with especial flow software as below:

I try to plot countour in matlab with below code but it gives wrong results.

xyz=dlmread('velocity.txt');

x=xyz(:,1);

y=xyz(:,2);

z=xyz(:,3);

[X,Y]=meshgrid(min(x):max(x),min(y):max(y));

Z=griddata(x,y,z,X,Y);

contourf(X,Y,Z)

Which code I need to create velocity countour similar to first image? Thank you.

Note: I uploaded my data as an attachment.

Answer 1

[Voss]

The x and y don't quite make a grid (a point is missing in the upper-left corner near (0,2)):

xyz = readmatrix('velocity.txt');

plot(xyz(:,1),xyz(:,2),'.')

so it's most convenient to use a scatteredInterpolant:

I = scatteredInterpolant(xyz(:,1),xyz(:,2),xyz(:,3));

[x,y] = meshgrid(unique(xyz(:,1)),unique(xyz(:,2)));

contourf(x,y,I(x,y))

colorbar