kornia--kornia/tests/geometry/test_ransac.py

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# Copyright 2018 Kornia Team
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# Licensed under the Apache License, Version 2.0 (the "License");
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#     http://www.apache.org/licenses/LICENSE-2.0
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import pytest
import torch

from kornia.geometry import RANSAC, transform_points
from kornia.geometry.epipolar import sampson_epipolar_distance

from testing.base import BaseTester
from testing.casts import dict_to


class TestRANSACHomography(BaseTester):
    def test_smoke(self, device, dtype):
        torch.random.manual_seed(0)
        points1 = torch.rand(4, 2, device=device, dtype=dtype)
        points2 = torch.rand(4, 2, device=device, dtype=dtype)
        ransac = RANSAC("homography").to(device=device, dtype=dtype)
        torch.random.manual_seed(0)
        H, _ = ransac(points1, points2)
        assert H.shape == (3, 3)

    @pytest.mark.xfail(reason="might slightly and randomly imprecise due to RANSAC randomness")
    def test_dirty_points(self, device, dtype):
        # generate input data
        torch.random.manual_seed(0)

        H = torch.eye(3, dtype=dtype, device=device)
        H[:2] = H[:2] + 0.1 * torch.rand_like(H[:2])
        H[2:, :2] = H[2:, :2] + 0.001 * torch.rand_like(H[2:, :2])

        points_src = 100.0 * torch.rand(1, 20, 2, device=device, dtype=dtype)
        points_dst = transform_points(H[None], points_src)

        # making last point an outlier
        points_dst[:, -1, :] += 800
        ransac = RANSAC("homography", inl_th=0.5, max_iter=20).to(device=device, dtype=dtype)
        # compute transform from source to target
        dst_homo_src, _ = ransac(points_src[0], points_dst[0])

        self.assert_close(
            transform_points(dst_homo_src[None], points_src[:, :-1]), points_dst[:, :-1], rtol=1e-3, atol=1e-3
        )

    @pytest.mark.slow
    @pytest.mark.parametrize("data", ["loftr_homo"], indirect=True)
    def test_real_clean(self, device, dtype, data):
        # generate input data
        torch.random.manual_seed(0)
        data_dev = dict_to(data, device, dtype)
        homography_gt = torch.inverse(data_dev["H_gt"])
        homography_gt = homography_gt / homography_gt[2, 2]
        pts_src = data_dev["pts0"]
        pts_dst = data_dev["pts1"]
        ransac = RANSAC("homography", inl_th=0.5, max_iter=20).to(device=device, dtype=dtype)
        # compute transform from source to target
        dst_homo_src, _ = ransac(pts_src, pts_dst)

        self.assert_close(transform_points(dst_homo_src[None], pts_src[None]), pts_dst[None], rtol=1e-2, atol=1.0)

    @pytest.mark.slow
    @pytest.mark.xfail(reason="might slightly and randomly imprecise due to RANSAC randomness")
    @pytest.mark.parametrize("data", ["loftr_homo"], indirect=True)
    def test_real_dirty(self, device, dtype, data):
        # generate input data
        torch.random.manual_seed(0)
        data_dev = dict_to(data, device, dtype)
        homography_gt = torch.inverse(data_dev["H_gt"])
        homography_gt = homography_gt / homography_gt[2, 2]
        pts_src = data_dev["pts0"]
        pts_dst = data_dev["pts1"]

        kp1 = data_dev["loftr_outdoor_tentatives0"]
        kp2 = data_dev["loftr_outdoor_tentatives1"]

        ransac = RANSAC("homography", inl_th=3.0, max_iter=30, max_lo_iters=10).to(device=device, dtype=dtype)
        # compute transform from source to target
        dst_homo_src, _ = ransac(kp1, kp2)

        # Reprojection error of 5px is OK
        self.assert_close(transform_points(dst_homo_src[None], pts_src[None]), pts_dst[None], rtol=0.15, atol=5)

    @pytest.mark.skip(reason="find_homography_dlt is using try/except block")
    def test_jit(self, device, dtype):
        torch.random.manual_seed(0)
        points1 = torch.rand(4, 2, device=device, dtype=dtype)
        points2 = torch.rand(4, 2, device=device, dtype=dtype)
        model = RANSAC("homography").to(device=device, dtype=dtype)
        model_jit = torch.jit.script(RANSAC("homography").to(device=device, dtype=dtype))
        self.assert_close(model(points1, points2)[0], model_jit(points1, points2)[0], rtol=1e-4, atol=1e-4)


class TestRANSACHomographyLineSegments(BaseTester):
    def test_smoke(self, device, dtype):
        torch.random.manual_seed(0)
        points1 = torch.rand(4, 2, 2, device=device, dtype=dtype)
        points2 = torch.rand(4, 2, 2, device=device, dtype=dtype)
        ransac = RANSAC("homography_from_linesegments").to(device=device, dtype=dtype)
        torch.random.manual_seed(0)
        H, _ = ransac(points1, points2)
        assert H.shape == (3, 3)

    @pytest.mark.xfail(reason="might slightly and randomly imprecise due to RANSAC randomness")
    def test_dirty_points(self, device, dtype):
        # generate input data
        torch.random.manual_seed(0)

        H = torch.eye(3, dtype=dtype, device=device)
        H[:2] = H[:2] + 0.1 * torch.rand_like(H[:2])
        H[2:, :2] = H[2:, :2] + 0.001 * torch.rand_like(H[2:, :2])

        points_src_st = 100.0 * torch.rand(1, 20, 2, device=device, dtype=dtype)
        points_src_end = 100.0 * torch.rand(1, 20, 2, device=device, dtype=dtype)

        points_dst_st = transform_points(H[None], points_src_st)
        points_dst_end = transform_points(H[None], points_src_end)

        # making last point an outlier
        points_dst_st[:, -1, :] += 800
        ls1 = torch.stack([points_src_st, points_src_end], dim=2)
        ls2 = torch.stack([points_dst_st, points_dst_end], dim=2)

        ransac = RANSAC("homography_from_linesegments", inl_th=0.5, max_iter=20).to(device=device, dtype=dtype)
        # compute transform from source to target
        dst_homo_src, _ = ransac(ls1[0], ls2[0])

        self.assert_close(
            transform_points(dst_homo_src[None], points_src_st[:, :-1]), points_dst_st[:, :-1], rtol=1e-3, atol=1e-3
        )

    @pytest.mark.skip(reason="find_homography_dlt is using try/except block")
    def test_jit(self, device, dtype):
        torch.random.manual_seed(0)
        points1 = torch.rand(4, 2, 2, device=device, dtype=dtype)
        points2 = torch.rand(4, 2, 2, device=device, dtype=dtype)
        model = RANSAC("homography_from_linesegments").to(device=device, dtype=dtype)
        model_jit = torch.jit.script(RANSAC("homography_from_linesegments").to(device=device, dtype=dtype))
        self.assert_close(model(points1, points2)[0], model_jit(points1, points2)[0], rtol=1e-4, atol=1e-4)


class TestRANSACFundamental(BaseTester):
    def test_smoke(self, device, dtype):
        torch.random.manual_seed(0)
        points1 = torch.rand(8, 2, device=device, dtype=dtype)
        points2 = torch.rand(8, 2, device=device, dtype=dtype)
        ransac = RANSAC("fundamental").to(device=device, dtype=dtype)
        Fm, _ = ransac(points1, points2)
        assert Fm.shape == (3, 3)

    @pytest.mark.slow
    @pytest.mark.xfail(reason="might slightly and randomly imprecise due to RANSAC randomness")
    @pytest.mark.parametrize("data", ["loftr_fund"], indirect=True)
    def test_real_clean_8pt(self, device, dtype, data):
        torch.random.manual_seed(0)
        # generate input data
        data_dev = dict_to(data, device, dtype)
        pts_src = data_dev["pts0"]
        pts_dst = data_dev["pts1"]
        # compute transform from source to target
        ransac = RANSAC("fundamental", inl_th=0.5, max_iter=20, max_lo_iters=10).to(device=device, dtype=dtype)
        fundamental_matrix, _ = ransac(pts_src, pts_dst)
        gross_errors = (
            sampson_epipolar_distance(pts_src[None], pts_dst[None], fundamental_matrix[None], squared=False) > 1.0
        )
        assert gross_errors.sum().item() == 0

    @pytest.mark.slow
    @pytest.mark.xfail(reason="might fail, because out F-RANSAC is not yet 7pt")
    @pytest.mark.parametrize("data", ["loftr_fund"], indirect=True)
    def test_real_clean_7pt(self, device, dtype, data):
        torch.random.manual_seed(0)
        # generate input data
        data_dev = dict_to(data, device, dtype)
        pts_src = data_dev["pts0"]
        pts_dst = data_dev["pts1"]
        # compute transform from source to target
        ransac = RANSAC("fundamental_7pt", inl_th=1.0, max_iter=100, max_lo_iters=10).to(device=device, dtype=dtype)
        fundamental_matrix, _ = ransac(pts_src, pts_dst)
        gross_errors = (
            sampson_epipolar_distance(pts_src[None], pts_dst[None], fundamental_matrix[None], squared=False) > 1.0
        )
        assert gross_errors.sum().item() == 0

    @pytest.mark.slow
    @pytest.mark.xfail(reason="might slightly and randomly imprecise due to RANSAC randomness")
    @pytest.mark.parametrize("data", ["loftr_fund"], indirect=True)
    def test_real_dirty_8pt(self, device, dtype, data):
        torch.random.manual_seed(0)
        # generate input data
        data_dev = dict_to(data, device, dtype)
        pts_src = data_dev["pts0"]
        pts_dst = data_dev["pts1"]

        kp1 = data_dev["loftr_indoor_tentatives0"]
        kp2 = data_dev["loftr_indoor_tentatives1"]

        ransac = RANSAC("fundamental", inl_th=1.0, max_iter=20, max_lo_iters=10).to(device=device, dtype=dtype)
        # compute transform from source to target
        fundamental_matrix, _ = ransac(kp1, kp2)
        gross_errors = (
            sampson_epipolar_distance(pts_src[None], pts_dst[None], fundamental_matrix[None], squared=False) > 10.0
        )
        assert gross_errors.sum().item() < 2

    @pytest.mark.slow
    @pytest.mark.xfail(reason="might fail, because this F-RANSAC is not 7pt")
    @pytest.mark.parametrize("data", ["loftr_fund"], indirect=True)
    def test_real_dirty_7pt(self, device, dtype, data):
        torch.random.manual_seed(0)
        # generate input data
        data_dev = dict_to(data, device, dtype)
        pts_src = data_dev["pts0"]
        pts_dst = data_dev["pts1"]

        kp1 = data_dev["loftr_indoor_tentatives0"]
        kp2 = data_dev["loftr_indoor_tentatives1"]

        ransac = RANSAC("fundamental_7pt", inl_th=1.0, max_iter=20, max_lo_iters=10).to(device=device, dtype=dtype)
        # compute transform from source to target
        fundamental_matrix, _ = ransac(kp1, kp2)
        gross_errors = (
            sampson_epipolar_distance(pts_src[None], pts_dst[None], fundamental_matrix[None], squared=False) > 10.0
        )
        assert gross_errors.sum().item() < 2

    @pytest.mark.skip(reason="try except block in python version")
    def test_jit(self, device, dtype):
        torch.random.manual_seed(0)
        points1 = torch.rand(8, 2, device=device, dtype=dtype)
        points2 = torch.rand(8, 2, device=device, dtype=dtype)
        model = RANSAC("fundamental").to(device=device, dtype=dtype)
        model_jit = torch.jit.script(model)
        self.assert_close(model(points1, points2)[0], model_jit(points1, points2)[0], rtol=1e-3, atol=1e-3)

    @pytest.mark.skip(reason="RANSAC is random algorithm, so Jacobian is not defined")
    def test_gradcheck(self, device):
        torch.random.manual_seed(0)
        points1 = torch.rand(8, 2, device=device, dtype=torch.float64, requires_grad=True)
        points2 = torch.rand(8, 2, device=device, dtype=torch.float64)
        model = RANSAC("fundamental").to(device=device, dtype=torch.float64)

        def gradfun(p1, p2):
            return model(p1, p2)[0]

        self.gradcheck(gradfun, (points1, points2), fast_mode=False, requires_grad=(True, False, False))


class TestRansacMethods:
    def test_max_samples_by_conf(self):
        """Test max_samples_by_conf with realistic scenarios."""
        conf = 0.99

        # Test 1: Very few inliers (1 out of 1000) with sample_size=7
        # Returns 1 because n_inl <= sample_size (early exit condition)
        x = RANSAC.max_samples_by_conf(n_inl=1, num_tc=1000, sample_size=7, conf=conf)
        assert x == 1  # Early exit when n_inl <= sample_size

        # Test 2: Low inlier ratio (10 out of 1000, 1%) with sample_size=7
        # Should require many iterations
        x = RANSAC.max_samples_by_conf(n_inl=10, num_tc=1000, sample_size=7, conf=conf)
        assert x > 0
        # With 1% inliers, probability of all 7 samples being inliers is very low
        # So we need a huge number of samples
        assert x > 1_000_000  # Should be a very large number

        # Test 3: Medium inlier ratio (500 out of 1000, 50%) with sample_size=4
        # Should require moderate number of iterations
        x = RANSAC.max_samples_by_conf(n_inl=500, num_tc=1000, sample_size=4, conf=conf)
        assert x > 0
        # With 50% inliers, probability of all 4 samples being inliers is ~0.0625
        # So we need log(1-0.99)/log(1-0.0625) ≈ 70 samples
        assert 50 < x < 100

        # Test 4: High inlier ratio (900 out of 1000, 90%) with sample_size=4
        # Should require very few iterations
        x = RANSAC.max_samples_by_conf(n_inl=900, num_tc=1000, sample_size=4, conf=conf)
        assert x > 0
        # With 90% inliers, probability of all 4 samples being inliers is ~0.66
        # So we need log(1-0.99)/log(1-0.66) ≈ 4 samples
        assert x < 10

        # Test 5: Edge case - all points are inliers
        x = RANSAC.max_samples_by_conf(n_inl=100, num_tc=100, sample_size=4, conf=conf)
        assert x == 1  # Only need 1 sample if all are inliers

        # Test 6: Edge case - not enough points for sample
        x = RANSAC.max_samples_by_conf(n_inl=10, num_tc=10, sample_size=15, conf=conf)
        assert x == 1  # Returns 1 when num_tc <= sample_size

        # Test 7: Edge case - too few inliers (n_inl <= sample_size)
        x = RANSAC.max_samples_by_conf(n_inl=2, num_tc=1000, sample_size=4, conf=conf)
        assert x == 1  # Returns 1 when n_inl <= sample_size

        # Test 8: Edge case - confidence at boundaries
        x = RANSAC.max_samples_by_conf(n_inl=50, num_tc=100, sample_size=4, conf=1.0)
        assert x == 1  # Returns 1 when conf >= 1.0

        x = RANSAC.max_samples_by_conf(n_inl=50, num_tc=100, sample_size=4, conf=0.0)
        assert x == 1  # Returns 1 when conf <= 0.0

        # Test 9: Verify monotonicity - more inliers should require fewer samples
        x1 = RANSAC.max_samples_by_conf(n_inl=200, num_tc=1000, sample_size=4, conf=conf)
        x2 = RANSAC.max_samples_by_conf(n_inl=500, num_tc=1000, sample_size=4, conf=conf)
        x3 = RANSAC.max_samples_by_conf(n_inl=800, num_tc=1000, sample_size=4, conf=conf)
        assert x1 > x2 > x3  # More inliers = fewer samples needed


class TestRANSACSeed:
    def test_same_seed_reproducible(self, device, dtype):
        """Same seed should produce identical results across two calls."""
        torch.manual_seed(42)
        points1 = torch.rand(20, 2, device=device, dtype=dtype)
        points2 = torch.rand(20, 2, device=device, dtype=dtype)

        ransac = RANSAC("homography", inl_th=2.0, max_iter=5, seed=123).to(device=device, dtype=dtype)
        H1, inliers1 = ransac(points1, points2)
        H2, inliers2 = ransac(points1, points2)

        assert torch.allclose(H1, H2)
        assert torch.equal(inliers1, inliers2)

    def test_different_seeds_differ(self, device, dtype):
        """Different seeds should (very likely) produce different results."""
        torch.manual_seed(42)
        points1 = torch.rand(20, 2, device=device, dtype=dtype)
        points2 = torch.rand(20, 2, device=device, dtype=dtype)

        ransac_a = RANSAC("homography", inl_th=2.0, max_iter=5, seed=1).to(device=device, dtype=dtype)
        ransac_b = RANSAC("homography", inl_th=2.0, max_iter=5, seed=2).to(device=device, dtype=dtype)

        H_a, _ = ransac_a(points1, points2)
        H_b, _ = ransac_b(points1, points2)

        assert not torch.allclose(H_a, H_b)

    def test_no_seed_differs_from_seeded(self, device, dtype):
        """Without a seed, repeated calls should not be forced to be identical to a seeded call."""
        torch.manual_seed(0)
        points1 = torch.rand(20, 2, device=device, dtype=dtype)
        points2 = torch.rand(20, 2, device=device, dtype=dtype)

        ransac_seeded = RANSAC("homography", inl_th=2.0, max_iter=5, seed=42).to(device=device, dtype=dtype)
        H_s1, _ = ransac_seeded(points1, points2)
        H_s2, _ = ransac_seeded(points1, points2)
        # Seeded should be reproducible
        assert torch.allclose(H_s1, H_s2)

    def test_seed_stored_as_attribute(self, device, dtype):
        ransac = RANSAC("homography", seed=7)
        assert ransac.seed == 7

    def test_none_seed_stored(self, device, dtype):
        ransac = RANSAC("homography")
        assert ransac.seed is None