HashTSDF::fetchPointsNormals() emits points in a wrong way

[savuor]

System Information

OpenCV version: 5.x
Platform & compiler: all

Detailed description

The method Volume::fetchPointsNormals() should emit points that lie on a 0-surface.
However, this method for HashTSDF emits points for all non-empty voxels.

While such a set of points gives some impression about the scene objects' shapes, this is incorrect.

Probably there should be the same points as in marchingCubes()

Steps to reproduce

1. Run Volume/VolumeTestFixture.fetchPointsNormals tests with --test_debug flag or OPENCV_TEST_DEBUG=1 env var.
2. Compare resulting OBJ files produced by the tests in some 3D viewer.

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files (videos, images, onnx, etc)