fixed bad shape of markers (1x4) in several cases and added tests #3105

AleksandrPanov · 2021-11-11T16:39:30Z

Merge with extra: opencv/opencv_extra#935

detectMarkers() and refineDetectedMarkers() returns OutputArrayOfArrays corners and rejectedCorners with different dimensions (for similar cases).
This problem is only relevant for vector input.
In this case detectMarkers() always returns corners and rejectedCorners as vector<Mat>, with Mat dimension 4x1.
In this case refineDetectedMarkers() works differently, if it finds a new marker. Then the dimension of Mats inside the vector<Mat> changes from 4x1 to 1x4.
The reason for the problem is that detectMarkers() and refineDetectedMarkers() create corners and rejectedCorners with different ways.
Current tests show no errors because they use vector<vector<Point2f> > for corners and rejectedCorners. Also, the current tests only check the number of refined corners (dimension and value are not checked).

In this PR refineDetectedMarkers() for create OutputArrayOfArrays corners and rejectedCorners uses _copyVector2Output(), just like detectMarkers().

opencv_extra=fix_refineDetectedMarkers_shape

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I agree to contribute to the project under Apache 2 License.
To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
The PR is proposed to proper branch
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Patch to opencv_extra has the same branch name.
The feature is well documented and sample code can be built with the project CMake

alalek · 2021-11-18T04:17:15Z

modules/aruco/src/aruco.cpp

        _detectedCorners.create((int)finalAcceptedCorners.size(), 1, CV_32FC2);
        for(unsigned int i = 0; i < finalAcceptedCorners.size(); i++) {
-            _detectedCorners.create(4, 1, CV_32FC2, i, true);
+            _detectedCorners.create(1, 4, CV_32FC2, i, true);


Why?

Below we have 4,1 again: _rejectedCorners.create(4, 1, ...)

BTW, all usages from aruco module:

$ grep -Rn '.create(4, 1,' ./modules/aruco/ ./modules/aruco/src/aruco.cpp:584: out.create(4, 1, CV_32FC2, i); ./modules/aruco/src/aruco.cpp:591: out.create(4, 1, CV_32FC2, i); ./modules/aruco/src/aruco.cpp:598: out.create(4, 1, CV_32FC2, i); ./modules/aruco/src/aruco.cpp:696: _objPoints.create(4, 1, CV_32FC3); ./modules/aruco/src/aruco.cpp:1402: _detectedCorners.create(4, 1, CV_32FC2, i, true); ./modules/aruco/src/aruco.cpp:1420: _rejectedCorners.create(4, 1, CV_32FC2, i, true); ./modules/aruco/src/charuco.cpp:822: _diamondCorners.create(4, 1, CV_32FC2, i, true);

It is surprising that the dimension of the matrices out[i], _objPoints[i], _detectedCorners[i], _rejectedCorners[i], _diamondCorners[i] is: (1 (rows) , 4 (cols)). But create with (4 (rows), 1 (cols)) was used.

Flag allowTransposed is ignored in this case (same values for true/false).
Looks like a bug in void _OutputArray::create(int _rows, int _cols, int mtype, int i, bool allowTransposed, int fixedDepthMask) const.

Such changes affecting API are considered as a "breaking change".

So proper and complete change should have:

clear justification

consistent solution (fix 1 place only and left 6 others is not a good way)

adapt coding rules to avoid such/similar problems in the future.

surprising

There is allowTransposed parameter on this line.

This strange code change is removed. Now refineDetectedMarkers() for create OutputArrayOfArrays corners and rejectedCorners uses _copyVector2Output(), just like detectMarkers().

It's strange that before detectMarkers() and refineDetectedMarkers() created OutputArrayOfArrays corners and rejectedCorners in different ways.

alalek · 2021-11-18T04:20:30Z

modules/aruco/test/test_charucodetection.cpp

+
+    aruco::detectMarkers(img, dico, corners, ids, detectorParams, rejectedPoints);
+    ASSERT_FALSE(corners.empty());
+    EXPECT_EQ(Size(4, 1), corners[0].size());


EXPECT_EQ(Size(4, 1), corners[0].size());

Why do you think that Size(1, 4) is wrong?

Size(1, 4) is not wrong (because it's just four 2d-points) , but corners[i] must be the same size in all cases to avoid undefined behavior.
I also think that InputOutputArrayOfArrays should not be used to pass array of pointers. You suggested replacing the InputOutputArrayOfArrays with a InputOutputArray with ndarray shape [npoints, 4, 2]. I'll try to do that.

Let me clarify:
In all tests and all examples in OpenCV detectMarkers and refineDetectedMarkers return corners with Size(4, 1) (for corners[i]). It is strange if this condition is violated for no reason.

AleksandrPanov · 2022-02-09T12:41:54Z

@alalek, could you recheck PR? I changed the description of the PR. Code changes are made more clear. PR description has been improved.

AleksandrPanov · 2022-02-09T12:48:23Z

modules/aruco/src/aruco.cpp

-        _detectedCorners.clear();
-        _detectedIds.clear();
-
        // parse output
        Mat(finalAcceptedIds).copyTo(_detectedIds);
-
-        _detectedCorners.create((int)finalAcceptedCorners.size(), 1, CV_32FC2);
-        for(unsigned int i = 0; i < finalAcceptedCorners.size(); i++) {
-            _detectedCorners.create(4, 1, CV_32FC2, i, true);
-            for(int j = 0; j < 4; j++) {
-                _detectedCorners.getMat(i).ptr< Point2f >()[j] =
-                    finalAcceptedCorners[i].ptr< Point2f >()[j];
-            }
-        }
+        _copyVector2Output(finalAcceptedCorners, _detectedCorners);

        // recalculate _rejectedCorners based on alreadyIdentified
-        vector< Mat > finalRejected;
+        vector<vector<Point2f> > finalRejected;
        for(unsigned int i = 0; i < alreadyIdentified.size(); i++) {
            if(!alreadyIdentified[i]) {
                finalRejected.push_back(_rejectedCorners.getMat(i).clone());
            }
        }
-
-        _rejectedCorners.clear();
-        _rejectedCorners.create((int)finalRejected.size(), 1, CV_32FC2);
-        for(unsigned int i = 0; i < finalRejected.size(); i++) {
-            _rejectedCorners.create(4, 1, CV_32FC2, i, true);
-            for(int j = 0; j < 4; j++) {
-                _rejectedCorners.getMat(i).ptr< Point2f >()[j] =
-                    finalRejected[i].ptr< Point2f >()[j];
-            }
-        }
+        _copyVector2Output(finalRejected, _rejectedCorners);


Now, refineDetectedMarkers() uses _copyVector2Output() to copy, just as detectMarkers() does.

alalek

Well done 👍

AleksandrPanov mentioned this pull request Nov 11, 2021

fixed bad shape of markers (1x4) in several cases and added tests opencv/opencv_extra#935

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AleksandrPanov self-assigned this Nov 11, 2021

AleksandrPanov force-pushed the fix_refineDetectedMarkers_shape branch 2 times, most recently from 6df7b11 to 9b8394a Compare November 12, 2021 09:18

AleksandrPanov requested a review from alalek November 16, 2021 18:59

alalek reviewed Nov 18, 2021

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AleksandrPanov marked this pull request as draft November 29, 2021 16:57

AleksandrPanov mentioned this pull request Jan 31, 2022

refineDetectedMarkers return different arrays depending on if new markers were found #2720

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AleksandrPanov linked an issue Jan 31, 2022 that may be closed by this pull request

refineDetectedMarkers return different arrays depending on if new markers were found #2720

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AleksandrPanov force-pushed the fix_refineDetectedMarkers_shape branch 7 times, most recently from 8f02cad to 211d636 Compare February 1, 2022 15:56

fixed bad shape of markers (1x4) in several cases and added tests

d72a91f

AleksandrPanov force-pushed the fix_refineDetectedMarkers_shape branch from 211d636 to d72a91f Compare February 1, 2022 16:16

AleksandrPanov marked this pull request as ready for review February 7, 2022 11:36

AleksandrPanov commented Feb 9, 2022

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alalek approved these changes Feb 9, 2022

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opencv-pushbot merged commit ed0094c into opencv:3.4 Feb 9, 2022

AleksandrPanov mentioned this pull request Feb 9, 2022

cv::aruco::refineDetectedMarkers change detectedCorners[i] shape in some cases opencv/opencv#14014

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alalek mentioned this pull request Feb 10, 2022

(4.x) Merge 3.4 #3173

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alalek mentioned this pull request Feb 22, 2022

(5.x) Merge 4.x #3179

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