add part of opencv

Lib/opencv/sources/doc/tutorials/features2d/feature_description/feature_description.markdown

@@ -0,0 +1,51 @@
+Feature Description {#tutorial_feature_description}
+===================
+
+Goal
+----
+
+In this tutorial you will learn how to:
+
+-   Use the @ref cv::DescriptorExtractor interface in order to find the feature vector correspondent
+    to the keypoints. Specifically:
+    -   Use cv::xfeatures2d::SURF and its function cv::xfeatures2d::SURF::compute to perform the
+        required calculations.
+    -   Use a @ref cv::DescriptorMatcher to match the features vector
+    -   Use the function @ref cv::drawMatches to draw the detected matches.
+
+\warning You need the <a href="https://github.com/opencv/opencv_contrib">OpenCV contrib modules</a> to be able to use the SURF features
+(alternatives are ORB, KAZE, ... features).
+
+Theory
+------
+
+Code
+----
+
+@add_toggle_cpp
+This tutorial code's is shown lines below. You can also download it from
+[here](https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/features2D/feature_description/SURF_matching_Demo.cpp)
+@include samples/cpp/tutorial_code/features2D/feature_description/SURF_matching_Demo.cpp
+@end_toggle
+
+@add_toggle_java
+This tutorial code's is shown lines below. You can also download it from
+[here](https://github.com/opencv/opencv/tree/master/samples/java/tutorial_code/features2D/feature_description/SURFMatchingDemo.java)
+@include samples/java/tutorial_code/features2D/feature_description/SURFMatchingDemo.java
+@end_toggle
+
+@add_toggle_python
+This tutorial code's is shown lines below. You can also download it from
+[here](https://github.com/opencv/opencv/tree/master/samples/python/tutorial_code/features2D/feature_description/SURF_matching_Demo.py)
+@include samples/python/tutorial_code/features2D/feature_description/SURF_matching_Demo.py
+@end_toggle
+
+Explanation
+-----------
+
+Result
+------
+
+Here is the result after applying the BruteForce matcher between the two original images:
+
+![](images/Feature_Description_BruteForce_Result.jpg)