How select/crop geographic region on the basis of lat/lon values?

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Kamran Afroz
Kamran Afroz 2023-7-7
编辑： Pranavkumar Mallela 2023-7-27
I want to select/crop region on the basis of lat/lon.
I have geographical data with dimensions of lat,lon and time from which I want to crop a region using four lat/lon(e.g. LAT: 13,18; LON: 73,76) points like a rectangle.
I have attached my sample data for reference.
Can anyone help me with this problem?

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Pranavkumar Mallela
编辑：Pranavkumar Mallela 2023-7-27
Hi,
As per my understanding, you are trying to crop a region that is part of the sample data, which includes the 'rf' value over a 100x100 area and 48 time instances.
First use 'ncread' to read the 'rf' variable from the above attached file in the following way:
rf = ncread("test.nc", 'rf');
The variable 'rf' is a 100x100x48 double matrix. To crop a certain geographical region at a given time 't', you can use the following code:
cropped_region = rf(13:18, 73:76, t); % at a given time 't'
For more information regarding selection of data from a matrix, you can refer the following documentation: https://www.mathworks.com/help/matlab/math/array-indexing.html
Hope this helps! Thanks!
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Pranavkumar Mallela
Pranavkumar Mallela 2023-7-7
编辑：Pranavkumar Mallela 2023-7-27
Hey, thanks for clarifying that.
You can utilize the 'find' function to find the indices of the required latitude and longitude ranges.
The code is as follows:
lat = [1 2 3 4 5 6 7 8 9 10]; % assume this is your latitude data
lon = [1 2 3 4 5 6 7 8 9 10]; % assume this is your longitude data
% Set the required limits here
req_lat_ll = 13; req_lat_ul = 18;
req_lon_ll = 73; req_lon_ul = 76;
lat_ll = find(lat <= req_lat_ll ,1,'last'); % ll = lower limit
lat_ul = find(lat >= req_lat_ul,1,'first'); % ul = upper limit
lon_ll = find(lon <= req_lon_ll ,1,'last');
lon_ul = find(lon >= req_lon_ul,1,'first');
cropped_region = rf(lat_ll:lat_ul, lon_ll:lon_ul, t); % at a given time 't'
Now you should be able to access rainfall using latitude and longitude ranges.
For more information regarding the 'find' function, please refer to this documentation:
https://www.mathworks.com/help/matlab/matlab_prog/find-array-elements-that-meet-a-condition.html
Thanks! Hope this helps!

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