Interpolating scattered data within a shapefile/worldmap

Hi I have x,y,zi scattered data, where x is lon, y is lat and zi is the data, I want to interpolate and extrapolate the data within the land boundaries, I used

vq = griddata(x,y,zi,xi,yi);

However, the interpolation and extrapolation was not made as desired.

[BN]

Use scatteredInterpolant (https://www.mathworks.com/help/matlab/ref/scatteredinterpolant.html). It is very similar to griddata but I guess it inter polate across all area that you want.

[SChow]

I have tried using scatteredinterpolant, it does not work. Please find the attached file of scattered data.

clc
clear
[LAT LON]=cdtgrid(1.875);%%making meshgrid for desired data

obs_data=xlsread('Z:\CP_c.csv');

 loni = obs_data(:,2) ;
 lati = obs_data(:,1) ;
% zi = interp2(LONi,LATi,xi,loni,lati) ;

F=scatteredInterpolant(loni,lati,obs_data(:,5),'linear','linear');
F.Method = 'linear';
vq1 = F(LAT,LON);
imagesc(vq1)

Answer 1

[darova]

Here is my effort. Am i succeeded?

S = importdata('CP_c.csv');
A = S.data;
x = A(:,1);
y = A(:,2);
z = A(:,3);
xx = linspace(min(x),max(x),20);
yy = linspace(min(y),max(y),20);
[X,Y] = meshgrid(xx,yy);
Z = griddata(x,y,z,X,Y);
surf(X,Y,Z)

[SChow]

hi darova,

With your code (slightly changes), I get fig 1, I do not get desired results (see fig 2):

clc
clear
addpath ( 'Z: \ CDT \ chadagreene-CDT-dc37894 \ cdt \' )
S = importdata ( 'Z: \ NO2_WORK \ CP_c.csv' );
A = S.data;
x = A (:, 1);
y = A (:, 2);
z = A (:, 3);
% xx = linspace (min (x), max (x), 20);
% yy = linspace (min (y), max (y), 20);
[X, Y] = cdtgrid (0.5); %%% meshgrid at 0.5 degree res
Z = griddata (x, y, z, X, Y);
imagescn (X, Y, Z)

[darova]

It's not easy task. Do you have coordinates of each separate region? (black)

[SChow]

Hi darova,

Even if we can interpolate+extrapolate to the whole extent of fig1 (including the white portion), I can clip the otputs for oceans using island

Can you help me interpolate the point data to the extent of the globe?

[LAT, LON] = cdtgrid (0.5); %%% meshgrid of X and Y for the globe at 0.5 degree res

[darova]

I tried this

worldmap([min(x) max(x)],[min(y) max(y)])
load coast
plotm(lat, long)
hold on
plotm(x,y,'.g')
hold off

Looks like you don't have enough data for color

[darova]

Or scatter

scatterm(x,y,10,z,'fill')

[SChow]

I could plot similar scatter plot with fastscatter.

I need to interpolate the data from these points to the extent of the world

[darova]

You don't have points for RUssia and Mexico

[SChow]

Yes, that is why I want to interpolate the data to Mexico and Russia.