ChiSquareDistance problem about flann

[mariusmuja]

Since you mention you are using the flann_set_distance_type() function, I assume you are using the C bindings, is this correct? What version of FLANN are you using (1.7.1, trunk)? Can you include a small code snippet of your code?

[Marzounette]

Thanks for your response Marius.

Yes, i use the C bindings with FLANN 1.7.1.
Here is a snippet of my code :
//
FLANNParameters flann_params;
flann_params.checks = FLANN_CHECKS_UNLIMITED;
flann_params.eps = 0.0;
flann_params.trees = 1;
flann_params.algorithm = FLANN_INDEX_KDTREE;
flann_set_distance_type( FLANN_DIST_CHI_SQUARE, 0);

flann_index_t index_ptr;
flann_find_nearest_neighbors_index( index_ptr, testset, tcount, result, dists, nn, flann_params);
//

I'm looking for the nn exact nearest neighbors.
apparently the distance calculus is doing with the euclidian distance, not with the chi square distance.
There is a problem in my code?

Thanks,
Marzieh

[mariusmuja]

Hi Marzieh,

Your code looks fine, it should use the chi square distance. How did you
verify that is the euclidean distance instead?

Marius

On Fri, Aug 17, 2012 at 12:19 AM, Marzounette [email protected]:

Thanks for your response Marius.

Yes, i use the C bindings with FLANN 1.7.1.
Here is a snippet of my code :
//
FLANNParameters flann_params;
flann_params.checks = FLANN_CHECKS_UNLIMITED;
flann_params.eps = 0.0;
flann_params.trees = 1;
flann_params.algorithm = FLANN_INDEX_KDTREE;
flann_set_distance_type( FLANN_DIST_CHI_SQUARE, 0);

flann_index_t index_ptr;
flann_find_nearest_neighbors_index( index_ptr, testset, tcount, result,
dists, nn, flann_params);
//

I'm looking for the nn exact nearest neighbors.

apparently the distance calculus is doing with the euclidian distance, not
with the chi square distance.
There is a problem in my code?

Thanks,
Marzieh

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/60#issuecomment-7811500.

[Marzounette]

with printing in L2 and chisquare distance. Only L2 distance is actually performed.

Marzieh

[mariusmuja]

I cannot reproduce this. I've done the following changes:
added flann_set_distance_type( FLANN_DIST_CHI_SQUARE, 0); to examples/flann_example.c
and added printfs to L2 and ChiSquare distances in src/cpp/flann/algorithms/dists.h (see patch below)

If I recompile and run flann_example_c only the ChiSquare message gets printed.

Regards,
Marius

diff -Naur flann-1.7.1-src/examples/flann_example.c flann-1.7.1-src_/examples/flann_example.c
--- flann-1.7.1-src/examples/flann_example.c    2011-12-26 02:17:13.000000000 -0800
+++ flann-1.7.1-src_/examples/flann_example.c   2012-08-29 11:58:54.000000000 -0700
@@ -98,6 +98,7 @@
     p.trees = 8;
     p.log_level = FLANN_LOG_INFO;
        p.checks = 64;
+    flann_set_distance_type( FLANN_DIST_CHI_SQUARE, 0);

     printf("Computing index.\n");
     index_id = flann_build_index(dataset, rows, cols, &speedup, &p);
diff -Naur flann-1.7.1-src/src/cpp/flann/algorithms/dist.h flann-1.7.1-src_/src/cpp/flann/algorithms/dist.h
--- flann-1.7.1-src/src/cpp/flann/algorithms/dist.h     2011-12-26 02:17:13.000000000 -0800
+++ flann-1.7.1-src_/src/cpp/flann/algorithms/dist.h    2012-08-29 11:59:48.000000000 -0700
@@ -138,6 +138,7 @@
     template <typename Iterator1, typename Iterator2>
     ResultType operator()(Iterator1 a, Iterator2 b, size_t size, ResultType worst_dist = -1) const
     {
+        printf("In  L2 dist\n");
         ResultType result = ResultType();
         ResultType diff0, diff1, diff2, diff3;
         Iterator1 last = a + size;
@@ -683,6 +684,7 @@
     template <typename Iterator1, typename Iterator2>
     ResultType operator()(Iterator1 a, Iterator2 b, size_t size, ResultType worst_dist = -1) const
     {
+        printf("In ChiSquare dist\n");
         ResultType result = ResultType();
         ResultType sum, diff;
         Iterator1 last = a + size;