Fill inside a polygon with a color

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BN
BN on 3 May 2020
Commented: Patrick Laux on 13 Jul 2021
Dear all,
I want to fill a polygon that I readed from shapefile with blue in order to visualzing it as lake. I searched alot and tried:
S2 = shaperead('lake.shp');
polygonwater1_y = S2(1).X;
polygonwater1_x = S2(1).Y;
fill (polygonwater1_y,polygonwater1_x,'b')
And:
patch (polygonwater1_y,polygonwater1_x,'b')
But as you can see below, unfortunately, it doesn't fill:
Do you know how can I do to fill it?
Thank you
  2 Comments
BN
BN on 3 May 2020
Dear KSSV
I attached data here. There is my shapefile containing 3 lakes. I want to fill all of them by blue.
Thank you.

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Accepted Answer

KSSV
KSSV on 3 May 2020
Edited: KSSV on 3 May 2020
It happned because, your region have multiple regions inside and they have NaN's.
shfile = "Lakes/lakes.shp" ;
S = shaperead(shfile) ;
N = length(S) ;
x = S(3).X ; y = S(3).Y ; % Picked the 3rd region
idx = find(isnan(x)) ; % find positions of NaNs
idx = [1 idx length(x)] ; % append first and last position
figure
hold on
for i = 1:length(idx)-1
pos = idx(i):idx(i+1) ; % gEt the required position
xi = x(pos) ; yi = y(pos) ; % GEt the corodinates
% Remove NaN's
xi(isnan(xi)) = [] ;
yi(isnan(yi)) = [] ;
patch(xi,yi,'b') ; % color the area
end
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More Answers (1)

Steven Lord
Steven Lord on 26 Aug 2020
Another way to plot and work with this data is to create a polyshape for each region.
S = shaperead('lakes.shp');
for k = 1:numel(S)
P(k) = polyshape(S(k).X, S(k).Y); % This will issue a warning each time
end
plot(P(3), 'FaceColor', 'r')
% Or plot all of them
figure
plot(P)
Some of the functions for working with polyshape objects may be of use to you. For example, computing the area of the polyshape agrees pretty well with the Shape_Area from the shape file.
[area(P(3)); S(3).Shape_Area; area(P(3))-S(3).Shape_Area]
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