How to insert values in a zeros matrix?

Hello everyone,

I have created a zeros metrix X = 720x1440, the interval of each grid is 0.25. I have another matrix Y= 129x135, this matrix is having values. Now I want to insert the values of Y matrix into the X matrix.

The location of Y matrix is, 6.5:0.25:38.5 (129) and 66.5:0.25:100.0 (135)

Thank you

[Torsten]

Now I want to insert the values of Y matrix into the X matrix.

And at which positions of the X-matrix ?

[the cyclist]

You told us the grid interval, but we also need to know the grid starting point. Does X(1,1) correspond to grid location (0,0)?

[Aarti Soni]

@the cyclist @Torsten

0.25:0.25:360;

-89.75:0.25:90;

1440x720 is a global grid and 129x135 is the location of India. The location of India is given in question.

I hope this is clear.

Answer 1

[Voss]

all_lat = -89.75:0.25:90;
% according to the longitudes specified for India (66.5 to 100), 
% longitude goes from -180 to 180, not 0 to 360:
all_lon = (0.25:0.25:360)-180;

india_lat = 6.5:0.25:38.5;
india_lon = 66.5:0.25:100.0;

whos *_lat *_lon

  Name           Size              Bytes  Class     Attributes

  all_lat        1x720              5760  double              
  all_lon        1x1440            11520  double              
  india_lat      1x129              1032  double              
  india_lon      1x135              1080  double              

X = zeros(numel(all_lat),numel(all_lon)); % your zeros matrix
Y = rand(numel(india_lat),numel(india_lon)); % random matrix substituting for your Y matrix

% determine where Y belongs in X:
[~,idx_lat] = ismember(india_lat,all_lat);
[~,idx_lon] = ismember(india_lon,all_lon);
% set those elements of X to the values in Y:
X(idx_lat,idx_lon) = Y;

% plot to see the result
s = pcolor(all_lon,all_lat,X);
set(s,'EdgeColor','none');

[Aarti Soni]

@_ thanks for the code but I am getting values at this position.

[Voss]

One difference is that I used all_lon and all_lat as the x and y coordinates for my pcolor plot and you are using indices. Also, the 'YDir' of your axes is 'reverse'.

If I make those two changes I get your plot:

all_lat = -89.75:0.25:90;
% according to the longitudes specified for India (66.5 to 100), 
% longitude goes from -180 to 180, not 0 to 360:
all_lon = (0.25:0.25:360)-180;
india_lat = 6.5:0.25:38.5;
india_lon = 66.5:0.25:100.0;
whos *_lat *_lon

  Name           Size              Bytes  Class     Attributes

  all_lat        1x720              5760  double              
  all_lon        1x1440            11520  double              
  india_lat      1x129              1032  double              
  india_lon      1x135              1080  double              

X = zeros(numel(all_lat),numel(all_lon)); % your zeros matrix
Y = rand(numel(india_lat),numel(india_lon)); % random matrix substituting for your Y matrix
% determine where Y belongs in X:
[~,idx_lat] = ismember(india_lat,all_lat);
[~,idx_lon] = ismember(india_lon,all_lon);
% set those elements of X to the values in Y:
X(idx_lat,idx_lon) = Y;

% plot to see the result
% s = pcolor(all_lon,all_lat,X); % using all_lon and all_lat for x and y in pcolor
s = pcolor(X);                   % using 1:size(X,2), 1:size(X,1)
set(s,'EdgeColor','none');
set(gca(),'YDir','reverse');     % reverse the Y axis