added a sample of matching SURF feature points using kd-tree (example/match_kdtree.rb)

examples/match_kdtree.rb

@@ -0,0 +1,88 @@
+#!/usr/bin/env ruby
+# -*- mode: ruby; coding: utf-8-unix -*- 
+
+# A sample of matching SURF feature points using kd-tree
+# See http://tech.groups.yahoo.com/group/OpenCV/message/62318
+
+require 'opencv'
+include OpenCV
+
+USE_EXTENDED_DESCRIPTOR = true
+THRESHOLD = 1500
+DESCRIPTOR_SIZE = USE_EXTENDED_DESCRIPTOR ? 128 : 64
+
+img1 = CvMat.load('lenna.jpg', CV_LOAD_IMAGE_GRAYSCALE)
+img2 = CvMat.load('lenna-rotated.jpg', CV_LOAD_IMAGE_GRAYSCALE)
+
+puts 'Extracting features from img1 using SURF...'
+param = CvSURFParams.new(THRESHOLD, USE_EXTENDED_DESCRIPTOR)
+kp1, desc1 = img1.extract_surf(param)
+puts "found #{kp1.size} keypoints from img1"
+
+puts 'Extracting features from img2 using SURF...'
+kp2, desc2 = img2.extract_surf(param)
+puts "found #{kp2.size} keypoints from img2"
+
+puts 'Matching keypoints...'
+desc1mat = CvMat.new(kp1.size, DESCRIPTOR_SIZE, :cv32f, 1)
+desc2mat = CvMat.new(kp2.size, DESCRIPTOR_SIZE, :cv32f, 1)
+desc1.each_with_index { |desc, i|
+  desc.each_with_index { |d, j|
+    desc1mat[i, j] = CvScalar.new(d)
+  }
+}
+desc2.each_with_index { |desc, i|
+  desc.each_with_index { |d, j|
+    desc2mat[i, j] = CvScalar.new(d)
+  }
+}
+
+feature_tree = CvFeatureTree.new(desc1mat)
+results, distances = feature_tree.find_features(desc2mat, 1, 250)
+
+reverse_lookup = []
+reverse_lookup_dist = []
+kp1.size.times { |i|
+  reverse_lookup << -1
+  reverse_lookup_dist << Float::MAX
+}
+
+match_count = 0
+kp2.size.times { |j|
+  i = results[j][0].to_i
+  d = distances[j][0]
+  if (d < reverse_lookup_dist[i])
+    match_count += 1 if reverse_lookup_dist[i] == Float::MAX
+    reverse_lookup[i] = j
+    reverse_lookup_dist[i] = d
+  end
+}
+puts "found #{match_count} putative correspondences"
+
+points1 = []
+points2 = []
+kp2.size.times { |j|
+  i = results[j][0].to_i
+  if (j == reverse_lookup[i])
+    points1 << kp1[i].pt
+    points2 << kp2[j].pt
+  end
+}
+
+width = img1.cols + img2.cols
+height = (img1.rows > img2.rows) ? img1.rows : img2.rows
+correspond = IplImage.new(width, height, :cv8u, 1);
+correspond.set_roi(CvRect.new(0, 0, img1.cols, img1.rows))
+img1.copy(correspond)
+correspond.set_roi(CvRect.new(img1.cols, 0, img1.cols + img2.cols, img2.rows))
+img2.copy(correspond)
+correspond.reset_roi
+
+points1.zip(points2) { |pt1, pt2|
+  pt2.x += img1.cols
+  correspond.line!(pt1, pt2, :color => CvColor::White)
+}
+
+GUI::Window.new('Object Correspond').show correspond
+GUI::wait_key
+