OpenCV/opencv/doc/tutorials/features2d/feature_homography/feature_homography.markdown

Features2D + Homography to find a known object {#tutorial_feature_homography}

@tableofcontents

@prev_tutorial{tutorial_feature_flann_matcher} @next_tutorial{tutorial_detection_of_planar_objects}

| | | | -: | :- | | Original author | Ana Huamán | | Compatibility | OpenCV >= 3.0 |

Goal

In this tutorial you will learn how to:

• Use the function @ref cv::findHomography to find the transform between matched keypoints.
• Use the function @ref cv::perspectiveTransform to map the points.

\warning You need the OpenCV contrib modules 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 @include samples/cpp/tutorial_code/features2D/feature_homography/SURF_FLANN_matching_homography_Demo.cpp @end_toggle

@add_toggle_java This tutorial code's is shown lines below. You can also download it from here @include samples/java/tutorial_code/features2D/feature_homography/SURFFLANNMatchingHomographyDemo.java @end_toggle

@add_toggle_python This tutorial code's is shown lines below. You can also download it from here @include samples/python/tutorial_code/features2D/feature_homography/SURF_FLANN_matching_homography_Demo.py @end_toggle

Explanation

Result

• And here is the result for the detected object (highlighted in green). Note that since the homography is estimated with a RANSAC approach, detected false matches will not impact the homography calculation.