finding distance between centroids

2012 4 12
1 个回答
更新时间：2019 3 11
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0 个投票

Hi
I have a group of blobs of a binary image for which I have calculated the centroids.
I would like to find the distance between each of these centroids and then extract the two centroids which lie in a 40 to 45 range. I've seperated the X and Y cdts into 2 matrices like so:
>> X=centroids(:,1); Y=centroids(:,2); >> X
X =
121.3073
142.9425
168.1000
225.5856
522.9487
>> Y
Y =
207.2626
149.0276
114.7667
297.5586
299.9551
and then I tried computing the euclidean distance using pdist2 but I dont understand what it gives me and I dont see any 40s over here
D = pdist2(X,Y,'euclidean'); >> D
D =
85.9553 27.7203 6.5406 176.2513 178.6479
64.3200 6.0851 28.1759 154.6160 157.0126
39.1626 19.0724 53.3333 129.4586 131.8551
18.3230 76.5580 110.8189 71.9730 74.3695
315.6861 373.9211 408.1821 225.3902 222.9936
Any advice pls?

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回答（1 个）

Andrei Bobrov
Andrei Bobrov 2012-4-12

1 个投票

try
D = dist([X,Y]')

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mayfair
mayfair 2012-4-12
Thanks andrei I just tried it and got this:
D = dist([X,Y]')
D =
0 62.1241 103.6583 137.9396 412.1987
62.1241 0 42.5054 169.9745 408.8812
103.6583 42.5054 0 191.6180 400.2654
137.9396 169.9745 191.6180 0 297.3728
412.1987 408.8812 400.2654 297.3728 0
I realised that dist and pdist2 actually computes distance between each X and Y which is not exactly what I want...
I'd like to be able to find the distance between each set of centroid coordinates and ideas on that pls?
Thanks!
Ashish Uthama
Ashish Uthama 2012-4-12
mayfair, try hand computing your expected result for a couple and compare with the above.
Example: Distance betwee first two points:
>> ( (X(1)-X(2))^2 + (Y(1)-Y(2))^2)^.5
ans =
62.1240
(Isnt that what Andrei's answer gives?)
mayfair
mayfair 2012-4-14
That's truue Ashish I managed to work it out I found that if you subtract the x and y matrices from its transposed matrix then use the hypot function it works like a charm :)
Rujal
Rujal 2016-2-5
hi mayfair..
My question is same as yours please give me a matlab code to find out distance between set of centroids. Thanks in advance.
Image Analyst
Image Analyst 2016-2-5
编辑：Image Analyst 2016-2-5
If you have the stats toolbox, you can use pdist2(). If not, just a simple for loop with vectorized distance calculation between that point and all the other points will do it.
Guillaume
Guillaume 2016-2-5
Even without the stats toolbox, you don't need a loop:
euclideandistance = hypot(bsxfun(@minus, X, X'), bsxfun(@minus, Y, Y'));
is all that's needed (assuming X and Y are vectors of the same size)
emami.m
emami.m 2019-3-11
Good job Guillaume,
It was a smart and exact solution.

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mayfair
mayfair
2012-4-12

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emami.m
emami.m
2019-3-11

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