How to filter out x-y coordinates and data from a plot, covering exactly the boundary of some region?

I want to extract the data that belongs exactly to within a particular boundary, but I don't know how to go about it.

[KSSV]

If your small region data falls beyond the main region data, then you can do extrapolation but this is not suggested. Why don't you show your domains pictorially so that we can get clear idea.

Answer 1

[Chad Greene]

To find points in a polygon use inpolygon, just as I suggested in the other post. If you're using Mouginot's annual velocity dataset, the coordinates are

 x = -2800000:1000:2800000; 
 y = (2800000:-1000:-2800000)';

and when you plot it you can use

imagesc(x,y,V) 
axis xy image

To find the pixels corresponding to Amery, get a grid of x,y points like this:

[X,Y] = mesghrid(x,y);

Then use inpolygon following the example I wrote for Wilkins Ice Shelf here.

Since you're using the Measures annual data, are you aware of the measuresann_interp function?

Answer 2

[KSSV]

You can get the points lying inside the closed region using inpolygon. Read about inpolygon.

[KSSV]

Okay..that case you pick the bounding box of your region of interest....make a grid using meshgrid and pick your (rectangular) part using interp2.

[Aditya Wahi]

I am very new to MATLAB, sir. Could you please explain me how to do that, in detail please.. Like what exactly will I achieve if I do this and how do I do it, if you don't mind.

[KSSV]

Attach your data...

[KSSV]

YOu may follow something like this:

I = imread('peppers.png') ;
I = rgb2gray(I) ;
[ny,nx] = size(I) ;
imshow(I) ;
pts = ginput(2) ;
[Xg,Yg] = meshgrid(1:nx,1:ny) ;
%%pick boudning box points
x0 = min(pts(:,1)) ; x1 = max(pts(:,1)) ;
y0 = min(pts(:,2)) ; y1 = max(pts(:,2)) ;
%%Make gird
N = 500 ;
x = linspace(x0,x1,N) ;
y = linspace(y0,y1,N) ;
[X,Y] = meshgrid(x,y) ;
%%do interpolation 
sub_I = interp2(Xg,Yg,double(I),X,Y) ;
sub_I = uint8(sub_I) ;
figure
imshow(sub_I) ;

When figure pops up....click on the region you want to extract.

[Aditya Wahi]

Sir, I tried using the code that you gave me, but rgb2gray command is giving me the following error:-

Error using rgb2gray>parse_inputs (line 82)
MAP must be a m x 3 array.

Error in rgb2gray (line 37)
X        = parse_inputs(X);

What can I do about this?

[KSSV]

That is for demo purpose.....you should not use rgb2gray there....