select a band of a matrix

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Andrea
Andrea 2012-5-28
Hello I want to select a band of a matrix with slop (S) and save them in another matrix.
a =
[ 1 2 3 4 5 6 7 8 9;
11 12 13 14 15 16 17 18 19;
21 22 23 24 25 26 27 28 29;
31 32 33 34 35 36 37 38 39;
41 42 43 44 45 46 47 48 49;
51 52 53 54 55 56 57 58 59]
Foe example I have a slope S1, and I want to select a band of this matrix in this way: Assume we can draw a line from array "6" to "29" and another line from "21" to "55". and remove the arrays above line 1 and below line 2. My problem is something like this but a little different. I have 2 slopes that I want to cut my matrix according with. Can you please help me to write a code for this problem?

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2012-5-28
[ii,jj]= ndgrid(1:size(a,1),1:size(a,2));
[I J] = find(ismember(a,[21;55;6;29]));
out = a.*(ii - I(1) > (diff(I(1:2)))/(diff(J(1:2)))*jj | ii - I(end) + 1< (diff(I(3:end)))/(diff(J(3:end)))*(jj - J(end)+1));

更多回答（1 个）

Image Analyst
Image Analyst 2012-5-28
I don't know what you're trying to explain. I can get the elements fo the array going from 6 to 29 and from 21 to 55 this way:
a =...
[ 1 2 3 4 5 6 7 8 9;
11 12 13 14 15 16 17 18 19;
21 22 23 24 25 26 27 28 29;
31 32 33 34 35 36 37 38 39;
41 42 43 44 45 46 47 48 49;
51 52 53 54 55 56 57 58 59]
aLinear = a'
aLinear = aLinear(:)
a_6_29 = aLinear(6:27)
a_21_55 = aLinear(21:50)
% Now what? I have no idea.
But I don't know what to do after that. Do you want to get a slope of a line fitted through those vectors? What does this mean: "remove the arrays above line 1 and below line 2."? To me that means you want line (row) 2 and nothing else, like this:
% Remove the arrays above line 1 and below line 2.
% That would leave only line 2 itself remaining.
a_new = a(2, :);
  2 个评论
Andrea
Andrea 2012-5-28
please see these images. That can help me to explain the problem better.
image 1: http://imageshack.us/photo/my-images/268/64770753.jpg/
image 2: http://imageshack.us/photo/my-images/405/52265040.jpg/
The fact is (as I explained weekly before) , I have two image matrix with both x and y of them. These two images has been taken with two different instruments (Satellite radar and ground radar) and have different spatial resolutions. I want to do somethings that really needs to have two image with exactly same geometric area. I don't want to define some specific points and change the image 1 according to image 2 because I have lots of other image from these two instruments. So I cannot define the intersection area (overlapping area) of each two images separately which may takes a lot of time. I want to write a program in Matlab which cut image 1 in the way it only has the data the image 2 already has. You can see that image 1 data has been defined in a band ( the blue band ) while image 1 has a circle form of data. I want to cut image 2 to have only this band area as image 1. I hope I explained the problem a little clearly than before.
Andrea
Andrea 2012-5-28
we can draw a line from array "6" to "29" and another line from "21" to "55". I want to remove arrays at the triangle made by the line 1 (from "6" to "29" a) and the the other triangle made at the left bottom corner of the matrix (from "6" to "29" ).

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