RotatedRect angle does not provide enough information (Bug #3735)

From http://stackoverflow.com/questions/24073127/opencvs-rotatedrect-angle-does-not-provide-enough-information, I think this can be solved this way:

RotatedRect rotated_rect = minAreaRect(contour);
float blob_angle_deg = rotated_rect.angle;
if (rotated_rect.size.width < rotated_rect.size.height) {
blob_angle_deg = 90 + blob_angle_deg;
}
Mat mapMatrix = getRotationMatrix2D(center, blob_angle_deg, 1.0);

So, in fact, RotatedRect's angle does not provide enough information for knowing an object's angle, you must also use RotatedRect's size.width and size.height.

Due to the number of questions about this issue in the Internet, maybe this should be clarified. Even if only in the documentation.

Contrarily to most of the other functions in OpenCV's API this feature seems difficult to understand. For instance, see http://shiyuzhao1.wordpress.com/2013/10/08/how-is-the-anlge-in-roatedrect-defined/ where the author writes "I bet you can never guess how the angle of a RoatedRect is defined."

What would be the disadvantages of making RotatedRect's angle consist in an value such that passing the symmetric to e.g. getRotationMatrix2D would allow to deskew the object enclosed by the RotatedRect?

OK. Are there instructions for that specific contribution type, i.e. how do I change the documentation in general terms? Thanks.

Basic guidelines can be found here: http://code.opencv.org/projects/opencv/wiki/How_to_contribute
As to the documentation, look at the rst files that are in each module, they contain the docs related to the modules.

Hi followed the steps in http://code.opencv.org/projects/opencv/wiki/How_to_contribute but I'm not being able to build the documentation.

I tried:

sphinx-build opencv/doc/ tmp

but:

writing output... [ 0%] index
Exception occurred:
File "/usr/local/lib/python2.7/dist-packages/Sphinx-1.2.2-py2.7.egg/sphinx/environment.py", line 1093, in get_doctree
f = open(doctree_filename, 'rb')
IOError: [Errno 2] No such file or directory: u'/home/jmss/tmp/.doctrees/index.doctree'

I also tried cmake, make, make install but in the installation directory there are no HTML or PDF files.

How can I generate the HTML or PDF for testing the chages I made to /modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst?

Thanks.

From OpenCV answers I was told to run "make doc" to generate the documentation. I was able to test the changes in PDF format. It seeems HTML files are not generated. Could not work out with sphinx, still.

I created the pull request.

make html_docs will build the HTML version. You can't use Sphinx directly, since we do some... tricky things with it.

Issue has been transferred to GitHub: https://github.com/Itseez/opencv/issues/4764