Fill inside a polygon with a color

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

[KSSV]

Atatch the data.

[BN]

Dear KSSV

I attached data here. There is my shapefile containing 3 lakes. I want to fill all of them by blue.

Thank you.

Answer 1

[KSSV]

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

[BN]

I am really thank you

[Abhishek Chakraborty]

Hi KSSV. Why have you picked the third region in this code?

[KSSV]

Because the user wanted the third region.

[Patrick Laux]

smart procedure

Answer 2

[Steven Lord]

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]

[Ishaan Chauhan]

Do you know of any ways to code to ignore the warnings?

[Patrick Laux]

warning off