bufferm works differently with the same data sets?

I am using bufferm to find buffer arounf letters of a name. The letter are consisting of segments in both clockwise and anti_clockwise. first file with name Name works perfect while the other file named Name_Shifted doesn't.

Both files are attached

Note: I have also used bufferm2 but didn't work !!!

Here is what is did for the first file Name:

BufferSize=0.3;

Segments=Name;
%Segments=Name_Shifted;
for L=1:length(Segments(:, 1))  
    xyz=Segments{L, 1};
    xyz1=[xyz;xyz(1,:)]; %To close the segment
    xyz2=xyz1;
    plot(xyz2(:,1),xyz2(:,2),'color',rand(1,3))
    hold on
    [x1,y1] = bufferm(xyz1(:,1),xyz1(:,2),BufferSize,'in');
    xyz3=[x1,y1];
    plot(xyz3(:,1),xyz3(:,2),'Color','k')
    hold on
end

and this was the result:

However, Here is what is did for the first file Name_Shifted :

BufferSize=0.3;

%Segments=Name;
Segments=Name_Shifted;
for L=1:length(Segments(:, 1))  
    xyz=Segments{L, 1};
    xyz1=[xyz;xyz(1,:)]; %To close the segment
    xyz2=xyz1;
    plot(xyz2(:,1),xyz2(:,2),'color',rand(1,3))
    hold on
    [x1,y1] = bufferm(xyz1(:,1),xyz1(:,2),BufferSize,'in');
    xyz3=[x1,y1];
    plot(xyz3(:,1),xyz3(:,2),'Color','k')
    hold on
end

and this was the result:

Answer 1

[Harikrishnan Balachandran Nair]

Hi Faiz,

I understand that you are trying to find the buffer zone inside your polygon using the 'bufferm' function. The 'bufferm' function expects the inputs to be in degrees, specifying the latitude and longitude.

However , In the 'Name_Shifted' mat file, i understand that you have shifted all the points in the 'x' and 'y' direction by a value of 200. when these values are given as input to the 'bufferm' function, it is perceived as latitudes and longitudes. This makes the latitude take values which is much more than 90 degree .This is the reason that the results are not as expected.

You can observe the issue by using 'geoplot' instead of 'plot' for plotting these polygons in the geographic co-ordinates.

[Faez Alkadi]

Hello Harikrishnan,

Thanks for your reply and explination. I solved the problem using polybuffer as you may see in the attached picture.

Thank you again

BufferSize=0.3;
xyzall=[];
NumOfBuf=3; % Number of times to buffer
 Segments=Name_Shifted;
for L=1:length(Segments(:, 1)) 
    xyz=Segments{L, 1};
    xyzall=[xyzall;xyz;NaN NaN NaN];
end

xyzall=[xyzall;xyzall(1,:)];% closre the polygon
polyline = polyshape({xyzall(:,1)},{xyzall(:,2)}); % Build polyline to shrink it as may times as desired (NumOfBuf)

for i=1:NumOfBuf% For number of segments
    % shrink with amount of the BufferSize
    polyin = polybuffer(polyline,-(i*BufferSize));
    plot (polyin);
    hold on
end