how to show only a part of a surface fit that falls within a certain polygon

Hi, i have created a surface fit using the next code:

*ft = 'thinplateinterp';

[fitresult, gof] = fit( [xData, yData], zData, ft );*

the next thing i want to do is to plot that surface, so i use:

*figure( 'Name', 'untitled fit 2' );

h = plot(fitresult);*

the problem is that it creats the surface over areas that i am not intrested in, so i have two parameters x and y that creats a closed polygon and i would like to show the part of the surface that falls within this polygon. how can i do it? is it even possible?

thank you for your help

Answer 1

[Mike Garrity]

The simplest is to set zData to nan for the points you want to discard. Consider this example:

[x,y,z] = peaks;
px = [0 4 2];
py = [-1 -1 2];
inpts = inpolygon(x,y,px,py);
z(inpts) = nan;
surf(x,y,z)

[Dany]

it is the simplest way but it won't work here because when i use the

[fitresult, gof] = fit( [xData, yData], zData, ft );

command i dont have access to the "fitresult" variable which holds the z components of the fitted surface.

also, i want to discard data outside the polygon and not inside.

[Mike Garrity]

When you said "show" I assumed you meant you wanted to modify the surface which gets created by the plot method. Also, to discard the data outside, just do z(~inputs). Like so:

[x,y,z] = peaks;
f = fit([x(:),y(:)],z(:),'poly23');
h = plot(f);
px = [-1 3 3 2 2 0 0 -1];
py = [-1 -1 0 0 1 1 0 0];
inpts = inpolygon(h.XData,h.YData,px,py);
h.ZData(~inpts) = nan;

[Dany]

ok. thank you. but one problem though.

when i write

inpts = inpolygon(h.XData,h.YData,px,py);

i get this error:

Attempt to reference field of non-structure array.

it is like "h" does not have any properties.