Calculate the distance between matched points

Hello,

I have two sets of matched points (matchedPoints1 and matchedPoints2, the size is 142x1 and the type is SURFPoints) and I want to calculate the distance between them. I tried the function pdist2() like this :

dist_matchedPoints=pdist2(matchedPoints1,matchedPoints2,'euclidean');

But I got the following error :

Error using cast

Unsupported data type for conversion: 'double'.

Error in pdist2 (line 250)

X = cast(X,outClass);

I don't really understand the meaning of this error message so can somebody help me to solve this problem ?

Thanks a lot.

[Adam Danz]

Do you want to calculate the distance between matchedPoints1(n) and matchedPoints2(n) to create a vector of distances or do you want to calculate the distance between every point in matchedPoints1 and every point in matchedPoints2 to create a matrix of distances?

[Théodore Keller]

I want to calculate the between every point in matchedPoints1 and every point in matchedPoints2 yes, so to create a matrix.

[Adam Danz]

Cool. See the last line of code in my answer using pdist2().

[Théodore Keller]

Thank you Adam. Just one last thing, I got a 172 x 172 matrix, is that mean that there are 172 matched points and for example the 10 x 20 value is the distance between the 10th matchedpoints1 and 20th matchedpoints2 ? Is the distance in pixel ?

[Adam Danz]

Glad I could help!

From the documentation,

The output 'd' (in my example) is the pairwise distances, 
returned as a numeric matrix.

If you do not specify either 'Smallest' or 'Largest', then 
D is an mx-by-my matrix, where mx and my are the number of 
observations in X and Y, respectively. D(i,j) is the distance 
between observation i in X and observation j in Y. If 
observation i in X or observation j in Y contains NaN, then 
D(i,j) is NaN for the built-in distance functions.

If you specify either 'Smallest' or 'Largest' as K, then 
D is a K-by-my matrix. D contains either the K smallest 
or K largest pairwise distances to observations in X for 
each observation in Y. For each observation in Y, pdist2 
inds the K smallest or largest distances by computing and 
comparing the distance values to all the observations in X. 
If K is greater than mx, pdist2 returns an mx-by-my matrix.

Answer 1

[Adam Danz]

The (x,y) point locations are stored in the "Locations" property of a SURFpoints object. If you are calculating the distance between matchedPoints1(n) and matchedPoints2(n), follow this example

%matchedPoints1 & matchedPoints2 are SURFpoints objects

distanceFcn = @(x1,x2,y1,y2)sqrt((x2-x1).^2 + (y2-y1).^2);  %distance function 

d = distanceFcn( ...
    matchedPoints1.Location(:,1),...
    matchedPoints2.Location(:,1),...
    matchedPoints1.Location(:,2),...
    matchedPoints2.Location(:,2)); 

% d(n) is the distance between matchPoints1.Location(n) and matchPoints2.Location(n)

To calculate the pairwise distance,

d = pdist2(matchedPoints1.Location,matchedPoints2.Location,'euclidean')