Obtaining the values within the boundary of my map

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Benyamin Nemati 2020-10-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/613881-obtaining-the-values-within-the-boundary-of-my-map

编辑： Benyamin Nemati 2020-10-27

采纳的回答： KSSV

在 MATLAB Online 中打开

Hello everyone,

I have some plots that they're from a 180*360*12 matrix with a code like this:

for i = 1:12
load coast
figure(i)
hold on
imagesc(lambda-180,phi,EWT(:,:,i));
plot(long,lat,'k');
end 
B_1 = shaperead('Aqueduct_river_basins_TIGRIS & EUPHRATES.shp');  %one of the shape files that ive loaded on my map
mapshow(B_1,'facecolor','none');  

you can see the boundaries on the map,the north africa and middle east region, now my question is: how could i derive EWT values within these boundaries, i want the average values on these areas at the end.

thanks for your considerations.

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KSSV 2020-10-14

inpolygon is your function..go for it.

Benyamin Nemati 2020-10-15

how can i use this function on my Z values (EWT(:,:,i)) as xq and yq ?

by considering my code, what is your suggestion?

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Answer 1

KSSV 2020-10-15

0
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https://ww2.mathworks.cn/matlabcentral/answers/613881-obtaining-the-values-within-the-boundary-of-my-map#answer_514693

在 MATLAB Online 中打开

Something like this:

[m,n,p] = size(EWT) ; 
[X,Y] = meshgrid(lambda-180,phi) ; 
B_1 = shaperead('Aqueduct_river_basins_TIGRIS & EUPHRATES.shp');  %one of the shape files that ive loaded on my map
N = length(B-1.X) ;    % this should have different regions 
iwant = cell(N,1) ; 
for i = 1:N
  % Get the indices insdie this polygon 
  idx = inpolygon(X,Y,B_1(i).X,B_i(i).Y) ; 
  % Get the mean of these points 
  thesum = 0 ; 
  for j = 1:p
    T = EWT(:,:,i) ; 
    thesum = thesum+T(idx) ; 
  end
  iwant{i} = thesum/p ;   
end

The above code gives you inside the polygon points as scattered points. If you want grid, pick the chunk, use inpoltgon and make the outside indices data to NaN.