Finding the closest coordinate from a surface plot based on a X, Y location

Hello, I want to extrapolate a point (longitude,latitude) from the coordinates of a surface file (attached here as "slab_strike") as it is empty (Strike=NaN) when using interp2 as the points are outside the boundary. Despite I used the option "nearest", it is empty anyway.

% Coordinates of the points:
lat_GMM= -17.8990;
lon_GMM=-73.5295;
% The surface plot
load slab_strike % Loading the slab strike
Slab_strike.x=x;
Slab_strike.y=y;
Slab_strike.z=z;
Strike = interp2(Slab_strike.x,Slab_strike.y,Slab_strike.z,lon_GMM,lat_GMM)

Strike = NaN

As Strike=NaN, there is a way I can choose the closest point value from the surface avoiding any NaN value and select the closest non-NaN value.

I would appreciate the help

Answer 1

[Voss]

load slab_strike

is_ok = ~isnan(z);
[X,Y] = meshgrid(x,y);
X = X(is_ok);
Y = Y(is_ok);
Z = z(is_ok);

lon_GMM = -73.5295;
lat_GMM = -17.8990;
[~,idx] = min((X-lon_GMM).^2+(Y-lat_GMM).^2);

figure()
hold on
surf(x,y,z,'EdgeColor','none')
h1 = plot(lon_GMM,lat_GMM,'.r');
h2 = plot3(X(idx),Y(idx),Z(idx),'.k');
legend([h1 h2],{'Requested Point','Nearest Non-NaN z'})

xlim(lon_GMM+[-5 5])
ylim(lat_GMM+[-5 5])

[Jorge Luis Paredes Estacio]

Thank you very much. I really appreaciated. It works perfectly :).

[Torsten]

@Jorge Luis Paredes Estacio

You should accept @Voss 's answer. It is univerally applicable for what you need.

[Jorge Luis Paredes Estacio]

Hi, it does not show me the option to accept it. Thank you.

[Voss]

@Jorge Luis Paredes Estacio: I believe that @Torsten is suggesting you unaccept his answer and accept mine.

[Jorge Luis Paredes Estacio]

I got it now. Done. Thank you :).

[Voss]

You're welcome!

Answer 2

[Torsten]

lat_GMM and lon_GMM are not within the rectangle in which data for z are supplied.

In this case, interp2 returns NaN because it does not extrapolate.

Choose lat_GMM and lon_GMM in the limits for x and y where values are given for z.

Else you could use

[~,idx] = min(abs(x-lon_GMM))
[~,idy] = min(abs(y-lat_GMM))
Strike = z(idy,idx)

But it seems that your z-matrix contains NaN values.

[Jorge Luis Paredes Estacio]

Thank your for your answer, Precicely, that is my question. How I can choose the closest point (Z value). Is there a specific function that can be used considering that the coordinates are not equally distributed as a vector to find the minimum distance?.

[Torsten]

The three lines of code should answer your question.

[Jorge Luis Paredes Estacio]

It is still provides a NaN value as the points x, y and z does not have a similar length. That means that If I want to plot x,y and z, I can use the surf function directly

surf(x,y,z)

[Torsten]

I don't know what you mean. The z-value in the point nearest to your lat and lon values is NaN.

% Coordinates of the points:
lat_GMM= -17.8990;
lon_GMM= -73.5295;
% The surface plot
load slab_strike % Loading the slab strike
Slab_strike.x=x;
Slab_strike.y=y;
Slab_strike.z=z;
[~,idx] = min(abs(x-lon_GMM));
x(idx)

ans = -73.5500

[~,idy] = min(abs(y-lat_GMM));
y(idy)

ans = -17.9000

Strike = z(idy,idx)

Strike = NaN

[Jorge Luis Paredes Estacio]

Thank you for your replied. That is correct, the selection should be based of finding the closest point withouth having a NaN value in the Z coordinate. A NaN value won't be useful for my analysis. In other words, it should skip that coordinate and choose another until it provides a non-NaN value.

[Torsten]

Then try whether z is NaN in the 8 points surrounding (x(idx),y(idy)).

If this also doesn't work, test z for NaN in the 16 following points and so on.

Answer 3

[Matt J]

F=griddedInterpolant({Slab_strike.x,Slab_strike.y},Slab_strike.z,'linear','nearest');

Strike = F(lon_GMM,lat_GMM);

[Torsten]

Most probably

F=griddedInterpolant({Slab_strike.x,Slab_strike.y},Slab_strike.z.','linear','nearest');

instead of

F=griddedInterpolant({Slab_strike.x,Slab_strike.y},Slab_strike.z,'linear','nearest');

[Jorge Luis Paredes Estacio]

Thank you for your answer. I got this error:

Error using griddedInterpolant

Sample points vector corresponding to grid dimension 1 must contain 1281 elements

[Jorge Luis Paredes Estacio]

Thank you. The error dissapeared, but Strike provides a NaN value

Strike=NaN;

[Matt J]

I assume the issue is resolved, since you accept-clicked Torsten's answer?

[Torsten]

@Jorge Luis Paredes Estacio

Thank you. The error dissapeared, but Strike provides a NaN value

Strike=NaN;

The z-value nearest to your latitude and longitude is NaN - the result you also got using interp2.

[Jorge Luis Paredes Estacio]

I still have the issue in selecting the closest point and avoiding as the same time the selection of any NaN value if that is the case. Thank you for your help.