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Griddata gives NaN values

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mehra
mehra on 21 Jun 2020
Commented: darova on 23 Jun 2020
Hello
In my code griddata gives NaN values, I checked if my query points are outside the convex hull of the sample data with the following code :
Xv=topologym_vert(:,1)/D;
Yv=topologym_vert(:,2)/D;
Zv=topologym_vert(:,3)/D;
ch=convhull(Xv,Zv)
plot(Xv(ch),Zv(ch),'r',xv,zv,'g')
and it seems everything is ok there,
So I wonder what else I have to change to get rid of NaN values?
the following is my code:
[xv,zv]=meshgrid(linspace((1/3),12,100),linspace(0.14,2.4,50));
aaa =
-0.0434 -0.0122 0.0507 0.2726 0.2433 0.2366 0.2452 -0.0344 -0.0225 0.0504 0.2446 0.2414
0.2426 0.2365 -0.0636 -0.0299 0.1221 0.2021 0.2335 0.2447 0.2399 -0.0342 -0.0002 0.0855
0.1676 0.2263 0.2327 0.2397 0.0827 0.0961 0.1150 0.1465 0.2199 0.2319 0.2346 0.0958
0.1031 0.1428 0.1659 0.2065 0.2332 0.2373 0.0896 0.0767 0.1249 0.1763 0.2160 0.2321
0.2334 0.1084 0.1224 0.1356 0.1621 0.2262 0.2353 0.0656 0.1133 0.1299 0.1539 0.2001
0.2315 0.2340 0.1426 0.1399 0.1321 0.2093 0.2289 0.1369 0.1675 0.1644 0.2151 0.2308
0.1828 0.1668 0.1648 0.1755 0.2038 0.2264 0.2319 0.2012 0.1875 0.2016 0.1872 0.2070
0.2210 0.2334
uvD=griddata(Xv,Zv,aaa,xv,zv);
Xv and Zv are attached.
Thanks.
  2 Comments
John D'Errico
John D'Errico on 21 Jun 2020
You do not provide the actual data, so it is impossible to know if the (xv,zv) points truly fall inside the convex hull of the data. All we have is your claim that the points appear to do so, when looking at a plot that we have not been given.
There are TWO possibilities, neither of which can be ruled out.
  1. One or more of your data points may have a NaN in it.
  2. the numbers you show with 2 significant digits 0.14 and 2.4, for example, are only approximations to the real range of your data.
I see one other inconsistency,
Yv=topologym_vert(:,2)/D;
I note that Yv is never used, yet I wonder if it may have been important.
mehra
mehra on 21 Jun 2020
Edited: mehra on 21 Jun 2020
yes Yv is not necessary here
I attached the actual data for Xv and Zv in my original question
thanks

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Answers (1)

darova
darova on 22 Jun 2020
I think you are using griddata in a wrong way
clc,clear
load Xv.mat
load Zv.mat
load data.txt
xx = linspace(min(Xv),max(Xv),20);
zz = linspace(min(Zv),max(Zv),20);
[xv,zv] = meshgrid(xx,zz); % create 2d mesh
yv = griddata(Xv,Zv,data,xv,zv); % interpolate data
plot3(Xv,Zv,data,'.r')
surface(xv,zv,yv)
axis vis3d
  2 Comments
mehra
mehra on 22 Jun 2020
Edited: mehra on 22 Jun 2020
I cant understand whats wrong with the way I use griddata, I am using it the same as yours but i use the required meshgrid and limits
[xv,zv]=meshgrid(linspace((1/3),12,100),linspace(0.2,2.4,50)); % This is Ok
Xv and Zv are also Ok,
But why the NaN values apear?
darova
darova on 23 Jun 2020
Don't see NaN

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