# Why does my surface have a 'jagged' look when I do this?

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A on 29 Apr 2015
Edited: pfb on 30 Apr 2015
Hi guys,
I think I have successfully done this. However, I would like to know the reason why I get a 'jagged' appearance on the bottom surface? and is there a way to make it smoother? Here's the code:
x = [0:100];
y = [0:100];
Test1 = @(x,y)(x+y);
Test2 = @(x,y)(x.^2+y);
[X1,Y1] = meshgrid(x,y);
Z1 = Test1(X1,Y1);
Z2 = Test2(X1,Y1);
i = Z1<50;
Z1(i)=NaN;
s1 = surf(X1,Y1,Z1);
hold on
i = Z2>=50;
Z2(i)=NaN;
s2 = surf(X1,Y1,Z2);
Thanks

Joseph Cheng on 30 Apr 2015
It is due to the spacing of your points. the data is being graphed in a grid so you're not going to have a nice straight line connecting the diagonals of the grid. you can reduce the jagged appearance by decreasing the spacing of the points. for instance if you try running your code with
x = [0:.5:100];
y = [0:.5:100];
you'll see that the jaggedness is decreased
##### 2 CommentsShowHide 1 older comment
Brendan Hamm on 30 Apr 2015
No, but you can turn the lines off.
surf(X1,Y1,Z1,'LineStyle','none')

pfb on 30 Apr 2015
Edited: pfb on 30 Apr 2015
Hi
Of course, making the grid thicker reduces the jaggedness.
As far as you are plotting planes, you can easily obtain nicer results.
Since these are planar manifolds, you can use one large patch instead of many small patches as in surf.
For that, look into "patch" or "fill3".
If you insist on using surf, you can use a grid adapted to your plane. That is: one of the directions should be the projection of the isolines, the other orthogonal to that (greatest gradient). You can see that when your plane depends only on X or Y. That should work also on your X.^2+Y, although you might want to use different spacings along the two lines.
Finally, you can perhaps use a triangulation for the original mesh. Look at "trisurf" and "delaunay".
Update I just realized you need to use a slightly different strategy for that.
For instance
x = [0:100];
y = [0:100];
Test1 = @(x,y)(x+y);
Test2 = @(x,y)(x.^2+y);
[X1,Y1] = meshgrid(x,y);
Z2 = Test2(X1,Y1);
i = Z2<=50;
X1=X1(i);
Y1=Y1(i);
Z2=Z2(i);
tri=delaunay(X1,Y1);
trisurf(tri,X1,Y1,Z2);
This eliminates the jaggedness. Also, I think you do not need a very thick grid for a nice result.