Add a new function that approximates the polygon bounding a convex hull with a certain number of sides #25607
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modules/imgproc/src/approx.cpp
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| if relevant = 0, the intersection in the heap must be recalculated | ||
| if relevant = 1, intersection has been calculated | ||
| */ | ||
| short relevant; |
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use int8_t instead of short or use enum class
Also suggest to rename relevant to pointStatus
asmorkalov
reviewed
Jun 4, 2024
| @@ -4060,6 +4060,26 @@ CV_EXPORTS_W void approxPolyDP( InputArray curve, | |||
| OutputArray approxCurve, | |||
| double epsilon, bool closed ); | |||
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| /** @brief Approximates a polygon with a convex hull with a specified accuracy and number of sides. | |||
| The cv::approxBoundingPoly function approximates a polygon with a convex hull | |||
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As soon as the implementation is base on public paper I propose to add the paper to doc/opencv.bib and add reference to the function description.
modules/imgproc/src/approx.cpp
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| int vertex; | ||
| cv::Point2f intersection; | ||
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| changes(float area_, int vertex_, cv::Point2f intersection_) |
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explicit?
const cv::Point2f&
modules/imgproc/src/approx.cpp
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| int next; | ||
| int prev; | ||
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| neighbours(int next_ = -1, int prev_ = -1, cv::Point2f point_ = { -1, -1 }) |
| CV_Assert(side > 2); | ||
| CV_Assert(_approxCurve.type() == CV_32FC2 | ||
| || _approxCurve.type() == CV_32SC2 | ||
| || _approxCurve.type() == 0); |
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The return type of the function matches the type OutputArray _approxCurve.
However, in Python, you don't need to specify OutputArray, and its type will be zero _approxCurve.type() == 0:
output = cv.approxBoundingPoly(contour, side=4, make_hull=True)In this case the function currently uses the InputArray _curve type for output:
if (_approxCurve.type()!= 0) depth = _approxCurve.depth();
modules/imgproc/src/approx.cpp
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| curve = curve.t(); | ||
| if (curve.rows == 1) | ||
| { | ||
| curve = curve.t(); | ||
| } |
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.t() call may happen twice. It does not make sense.
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Y can just call cv::Mat::reshape() to get propoer shape for existing buffer without memory transfers.
modules/imgproc/src/approx.cpp
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| if (recalculation(hull, vertex_id, area, new_x, new_y) == -1) | ||
| { | ||
| area = 1e+38f; |
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What 1d+38 means? I propose to use something like FLT_MAX instead.
modules/imgproc/src/approx.cpp
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| if (recalculation(hull, vertex_id, area, new_x, new_y) == -1) | ||
| { | ||
| area = 1e+38f; | ||
| new_x = -1; new_y = -1; |
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Also I propose to move the initialization for the negative case inside recalculation function.
modules/imgproc/src/approx.cpp
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| area = 1e+38f; | ||
| new_x = -1; new_y = -1; |
asmorkalov
reviewed
Jun 6, 2024
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| The algorithm based on the paper | ||
| <https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=1fbd43f3827fffeb76641a9c5ab5b625eb5a75ba>. |
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You can use Tex notation for references. Links are generated by doxygen automatically.
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Changes have been added. @asmorkalov
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merge PR with opencv/opencv_extra#1179
This PR is based on the paper View Frustum Optimization To Maximize Object’s Image Area.
Problem
I needed to reduce the number of vertices of the convex hull so that the additional area was minimal, andall vertices of the original contour enter the new contour.
Description
Initially in the contour of n vertices, at each stage we consider the intersection points of the lines formed by each adjacent edges. Each of these intersection points will form a triangle with vertices through which lines pass. Let's choose a triangle with the minimum area and merge the two vertices at the intersection point. We continue until there are more vertices than the specified number of sides of the approximated polygon.
Complexity:
Using a std::priority_queue or std::set time complexity is (O(n*ln(n)), memory O(n),
n - number of vertices in convex hull.
count of sides - the number of points by which we must reduce.
Comment
If epsilon_percentage more 0, algorithm can return more values than side.
Algorithm returns OutputArray. If OutputArray.type() equals 0, algorithm returns values with InputArray.type().
New test uses image which are not in opencv_extra, needs to be added.
Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
Patch to opencv_extra has the same branch name.