How extract boundary of red region in attached figure.

Hello All,

Actually, I want to make masking file of data above 1000m hight. I have already found a longitude and latitude of above 1000m height and plot that in red color but I want to just the boundary of this whole red plotted region. Please help me. Thank you so much in advance.

I am attaching figure and data. Below is code which I am using for plotting this.

z2 = z./9.8; z2 = z2';
xx = find((z2>1000));[x,y]=meshgrid(lons,lats);
plot(x,y,'*k')
hold on;plot(x(xx),y(xx),'*r');axis tight;

Answer 1

[Image Analyst]

Do you have the Image Processing Toolbox? If so, simply use bwboundaries().

[varunesh]

I tried but I am getting below error. I have already loaded data. Please help me. I tried but I unable to solve this problem.

Error using bwboundaries
 Expected input number 1, BW, to be two-dimensional.
 Error in bwboundaries>parseInputs (line 159)
 validateattributes(BW, {'numeric','logical'}, {'real','2d','nonsparse'}, ...
 Error in bwboundaries (line 128)
[BW, conn, findholes] = parseInputs(varargin{:});

[Image Analyst]

You have to pass it a binary image. What do you have? Do you have an RGB image with red and black? If so, do this

binaryImage = rgbImage(:, :, 1) > 0; % Extract red channel.
% bwboundaries() returns a cell array, where each cell contains the row/column coordinates for an object in the image.
% Plot the borders of all the coins on the original grayscale image using the coordinates returned by bwboundaries.
imshow(originalImage);
title('Outlines, from bwboundaries()', 'FontSize', captionFontSize); 
axis image; % Make sure image is not artificially stretched because of screen's aspect ratio.
hold on;
boundaries = bwboundaries(binaryImage);
numberOfBoundaries = size(boundaries, 1);
for k = 1 : numberOfBoundaries
  thisBoundary = boundaries{k};
  plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth', 2);
end
hold off;

[varunesh]

Simply, I want to longitude and latitude of this boundary (red region). Because I want to mask other datasets inside this polygon. Red region is showing surface hight above 1000m. Please load my data and see data then you can understand easily. In data, z is showing surface height. I generated this plot from my below code. Please use my below code for reading and plotting the data. Again thank you so much for giving me your prestigious time.

load data.mat;
z2 = z./9.8; z2 = z2';
xx = find((z2>1000));[x,y]=meshgrid(lons,lats);
plot(x,y,'*k')
hold on;plot(x(xx),y(xx),'*r');axis tight;

[Image Analyst]

I played around and I don't know how to do it with boundary and individual points. If you wanted to turn it into a digital image, it wouldn't be too hard. Just plot the points as a pixel, and call imclose() to close any small gaps, then call bwboundaries.

[varunesh]

Thank you so much for your helping nature. I also played a lot with this data but I am also not able to find a solution to this. Maybe god will be seen from the top and helping me with doing this.

If we will change this in a digital image then how can find the latitude and longitude of that boundary(point).

[Image Analyst]

What do you REALLY want to accomplish? If you get this as an image, what would it help you do that you cannot do now?

[varunesh]

I had already said that I want to longitude and latitude of all boundaries. With the help that boundaries I will mask the original data. I have already one example boundary of Tibet(Above to northern India). I am sending you this example boundary and code. You can see that how do I mask data above 1000m height from sea level from the help of this Tibet boundary.

    cst = load('tibet_bath1000.txt');
    inix = inpolygon(ln,lt,cst(:,1),cst(:,2));
    nnum(inix)=[];
    ln and lt is original logitude and latitude of data.