Features2D + Homography to find a known object

@tableofcontents

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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.

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