test: compare composite h5 mapping against ANTs

Author: oesteban

nitransforms/tests/test_io.py

@@ -781,33 +781,9 @@ def test_itk_h5_field_order_fortran(tmp_path):
     assert np.allclose(img.get_fdata(), expected)
 
 
-def test_composite_h5_map_against_ants(tmp_path):
+def test_composite_h5_map_against_ants(testdata_path, tmp_path):
     """Map points with NiTransforms and compare to ANTs."""
-    shape = (2, 2, 2)
-    disp = np.zeros(shape + (3,), dtype=float)
-    disp += np.array([0.2, -0.3, 0.4])
-
-    params = np.moveaxis(disp, -1, 0).reshape(-1, order="F")
-    fixed = np.array(
-        list(shape) + [0, 0, 0] + [1, 1, 1] + list(np.eye(3).ravel()), dtype=float
-    )
-    fname = tmp_path / "test.h5"
-    with H5File(fname, "w") as f:
-        grp = f.create_group("TransformGroup")
-        grp.create_group("0")["TransformType"] = np.array(
-            [b"CompositeTransform_double_3_3"]
-        )
-        g1 = grp.create_group("1")
-        g1["TransformType"] = np.array([b"DisplacementFieldTransform_float_3_3"])
-        g1["TransformFixedParameters"] = fixed
-        g1["TransformParameters"] = params
-        g2 = grp.create_group("2")
-        g2["TransformType"] = np.array([b"AffineTransform_double_3_3"])
-        g2["TransformFixedParameters"] = np.zeros(3, dtype=float)
-        g2["TransformParameters"] = np.array(
-            [1, 0, 0, 0, 1, 0, 0, 0, 1, 0.1, 0.2, -0.1], dtype=float
-        )
-
+    h5file, _ = _load_composite_testdata(testdata_path)
     points = np.array([[0.0, 0.0, 0.0], [1.0, 2.0, 3.0]])
     csvin = tmp_path / "points.csv"
     with open(csvin, "w") as f:
@@ -816,9 +792,7 @@ def test_composite_h5_map_against_ants(tmp_path):
             f.write(",".join(map(str, row)) + "\n")
 
     csvout = tmp_path / "out.csv"
-    cmd = (
-        f"antsApplyTransformsToPoints -d 3 -i {csvin} -o {csvout} -t {fname}"
-    )
+    cmd = f"antsApplyTransformsToPoints -d 3 -i {csvin} -o {csvout} -t {h5file}"
     exe = cmd.split()[0]
     if not shutil.which(exe):
         pytest.skip(f"Command {exe} not found on host")
@@ -827,9 +801,11 @@ def test_composite_h5_map_against_ants(tmp_path):
     ants_res = np.genfromtxt(csvout, delimiter=",", names=True)
     ants_pts = np.vstack([ants_res[n] for n in ("x", "y", "z")]).T
 
-    xforms = itk.ITKCompositeH5.from_filename(fname)
-    dfield = nitnl.DenseFieldTransform(xforms[0])
-    affine = nitl.Affine(xforms[1].to_ras())
-    mapped = (affine @ dfield).map(points)
+    xforms = itk.ITKCompositeH5.from_filename(h5file)
+    chain = (
+        nitl.Affine(xforms[0].to_ras())
+        + nitnl.DenseFieldTransform(xforms[1])
+    )
+    mapped = chain.map(points)
 
     assert np.allclose(mapped, ants_pts, atol=1e-6)