how to clip a domain data from global data?

I am trying to clip South Asia domain (19.25°E-116.25°E,-15.75°S-45.75°N) from a global dataset with 0.5 degree resolution.

Here is the code i am using:

global_data = load('global_data.mat');

% Define the latitude and longitude boundaries

lat_start = -15.75;

lat_end = 45.75;

lon_start = 19.25;

lon_end = 116.25;

% Define the resolution

resolution = 0.5;

% Calculate the indices for cropping

lat_indices = floor((lat_start + 90) / resolution) + 1 : floor((lat_end + 90) / resolution) + 1;

lon_indices = floor((lon_start + 180) / resolution) + 1 : floor((lon_end + 180) / resolution) + 1;

% Crop the global data

cropped_data = global_data(lat_indices, lon_indices, :);

% Display the size of the cropped data

disp(size(cropped_data));

Can someone help me with this?

Thank you.

Answer 1

[Sulaymon Eshkabilov]

Here are two ways to get it with two small corrections in your code:

Way - 1. Just use load() without variable name assigning, because the variable name is the same:

load('global_data.mat');

% Define the latitude and longitude boundaries
lat_start = -15.75;
lat_end = 45.75;
lon_start = 19.25;
lon_end = 116.25;
% Define the resolution
resolution = 0.5;
% Calculate the indices for cropping
lat_indices = floor((lat_start + 90) / resolution) + 1 : floor((lat_end + 90) / resolution) + 1;
lon_indices = floor((lon_start + 180) / resolution) + 1 : floor((lon_end + 180) / resolution) + 1;
% Crop the global data
cropped_data = global_data(lat_indices, lon_indices, :);
% Display the size of the cropped data
disp(size(cropped_data));

   124   195    12

Way - 2. Read data from Stucture variable, e.g.: global_data.global_data

global_data = load('global_data.mat');

global_data = load('global_data.mat');
% Define the latitude and longitude boundaries
lat_start = -15.75;
lat_end = 45.75;
lon_start = 19.25;
lon_end = 116.25;
% Define the resolution
resolution = 0.5;
% Calculate the indices for cropping
lat_indices = floor((lat_start + 90) / resolution) + 1 : floor((lat_end + 90) / resolution) + 1;
lon_indices = floor((lon_start + 180) / resolution) + 1 : floor((lon_end + 180) / resolution) + 1;
% Crop the global data
cropped_data = global_data.global_data(lat_indices, lon_indices, :);
% Display the size of the cropped data
disp(size(cropped_data));

   124   195    12

[Vidushi Koliyan]

Actually, i need to compare two data. I am attaching two figures. One is data i want to compare with (ori_im) and the clipped figure(clip_im). Now, extent of the domain is same that i am giving as input in my code. But it is not extracting correct domain. Can you suggest what could be the possible reason?

Answer 2

[Sulaymon Eshkabilov]

If understood your question correctly, what you want is to display your cropped data, right?

If so, here is how it can be done:

load('global_data.mat');
% Define the latitude and longitude boundaries
lat_start = -15.75;
lat_end = 45.75;
lon_start = 19.25;
lon_end = 116.25;
% Define the resolution
resolution = 0.5;
% Calculate the indices for cropping
lat_indices = floor((lat_start + 90) / resolution) + 1 : floor((lat_end + 90) / resolution) + 1;
lon_indices = floor((lon_start + 180) / resolution) + 1 : floor((lon_end + 180) / resolution) + 1;
% Crop the global data
cropped_data = global_data(lat_indices, lon_indices, :);
% Display the size of the cropped data
disp(size(cropped_data));

   124   195    12

figure
imagesc(cropped_data(:,:,1))   % Cropped data set

figure
imagesc(global_data(:,:,1))    % Whole data set

In order to create the two image as you mentioned, you need to specify the corodinates (indices) as in this cropped one.

[Vidushi Koliyan]

No. Actually the figure with "ori_im" name is the domain data that i need. And the coordinates are "South Asia domain (19.25°E-116.25°E,-15.75°S-45.75°N". But with these coordinates, i am getting the result (as you showed in your cropped_data figure) which is not correct domain data. So basically it is clipping a wrong domain.

Am I clear with my question? Sorry if i am not able to explain it correctly.