From 7d9541edb283d78b1ab998bec9bb379cc26a406c Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 20 Jul 2023 16:52:45 +0200
Subject: [PATCH 01/15] Load collada files

---
 pytransform3d/visualizer/_artists.py | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/pytransform3d/visualizer/_artists.py b/pytransform3d/visualizer/_artists.py
index 3aaec1b97..37ad3a212 100644
--- a/pytransform3d/visualizer/_artists.py
+++ b/pytransform3d/visualizer/_artists.py
@@ -554,7 +554,23 @@ class Mesh(Artist):
     """
     def __init__(self, filename, A2B=np.eye(4), s=np.ones(3), c=None,
                  convex_hull=False):
-        mesh = o3d.io.read_triangle_mesh(filename)
+        if filename.endswith(".dae"):
+            import collada
+            mesh = o3d.geometry.TriangleMesh()
+            try:
+                model = collada.Collada(filename)
+                for geometry in model.geometries:
+                    for primitive in geometry.primitives:
+                        p = o3d.geometry.TriangleMesh()
+                        vertices = primitive.vertex
+                        p.vertices = o3d.utility.Vector3dVector(vertices)
+                        triangles = primitive.vertex_index
+                        p.triangles = o3d.utility.Vector3iVector(triangles)
+                        mesh += p
+            except:
+                warnings.warn("Parsing collada file '%s' failed" % filename)
+        else:
+            mesh = o3d.io.read_triangle_mesh(filename)
         if convex_hull:
             self.mesh = mesh.compute_convex_hull()[0]
         else:

From 7ab3e538acb2b393c96291b06dfd4f5671239350 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 11:49:19 +0200
Subject: [PATCH 02/15] Extract mesh loader module

---
 pytransform3d/mesh_loader.py                | 50 +++++++++++++++++++++
 pytransform3d/plot_utils/_plot_functions.py | 20 +++------
 pytransform3d/visualizer/_artists.py        | 24 ++--------
 3 files changed, 59 insertions(+), 35 deletions(-)
 create mode 100644 pytransform3d/mesh_loader.py

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
new file mode 100644
index 000000000..079f96c09
--- /dev/null
+++ b/pytransform3d/mesh_loader.py
@@ -0,0 +1,50 @@
+import numpy as np
+
+
+def load_mesh(filename, convex_hull=False, return_as_open3d_mesh=False):
+    vertices = np.empty((0, 3), dtype=float)
+    triangles = np.empty((0, 3), dtype=int)
+    done = False
+
+    try:
+        import trimesh
+        geometry = trimesh.load(filename)
+        done = True
+
+        if isinstance(geometry, trimesh.Scene):
+            geometry = trimesh.util.concatenate(
+                list(geometry.geometry.values()))
+        if convex_hull:
+            geometry = geometry.convex_hull
+
+        vertices = geometry.vertices
+        triangles = geometry.faces
+
+        if return_as_open3d_mesh:
+            import open3d
+            return open3d.geometry.TriangleMesh(
+                open3d.utility.Vector3dVector(vertices),
+                open3d.utility.Vector3iVector(triangles))
+    except ImportError:
+        pass
+
+    try:
+        import open3d
+        mesh = open3d.io.read_triangle_mesh(filename)
+        done = True
+
+        if convex_hull:
+            mesh = mesh.compute_convex_hull()[0]
+
+        if return_as_open3d_mesh:
+            return mesh
+        else:
+            vertices = np.asarray(mesh.vertices)
+            triangles = np.asarray(mesh.triangles)
+    except ImportError:
+        pass
+
+    if not done:
+        raise IOError("Could not load mesh from '%s'" % filename)
+
+    return vertices, triangles
diff --git a/pytransform3d/plot_utils/_plot_functions.py b/pytransform3d/plot_utils/_plot_functions.py
index 171fe860c..ea4bb709e 100644
--- a/pytransform3d/plot_utils/_plot_functions.py
+++ b/pytransform3d/plot_utils/_plot_functions.py
@@ -6,6 +6,7 @@
 from ._artists import Arrow3D
 from ..transformations import transform, vectors_to_points
 from ..rotations import unitx, unitz, perpendicular_to_vectors, norm_vector
+from ..mesh_loader import load_mesh
 
 
 def plot_box(ax=None, size=np.ones(3), A2B=np.eye(4), ax_s=1, wireframe=True,
@@ -316,8 +317,8 @@ def plot_mesh(ax=None, filename=None, A2B=np.eye(4),
               convex_hull=False, alpha=1.0, color="k"):
     """Plot mesh.
 
-    Note that this function requires the additional library 'trimesh'.
-    It will print a warning if trimesh is not available.
+    Note that this function requires the additional library to load meshes
+    such as trimesh or open3d.
 
     Parameters
     ----------
@@ -364,20 +365,11 @@ def plot_mesh(ax=None, filename=None, A2B=np.eye(4),
             "package directory.")
         return ax
 
-    try:
-        import trimesh
-    except ImportError:
-        warnings.warn(
-            "Cannot display mesh. Library 'trimesh' not installed.")
-        return ax
-
-    mesh = trimesh.load(filename)
-    if convex_hull:
-        mesh = mesh.convex_hull
-    vertices = mesh.vertices * s
+    vertices, triangles = load_mesh(filename, convex_hull=convex_hull)
+    vertices = vertices * s
     vertices = np.hstack((vertices, np.ones((len(vertices), 1))))
     vertices = transform(A2B, vertices)[:, :3]
-    vectors = np.array([vertices[[i, j, k]] for i, j, k in mesh.faces])
+    vectors = np.array([vertices[[i, j, k]] for i, j, k in triangles])
     if wireframe:
         surface = Line3DCollection(vectors)
         surface.set_color(color)
diff --git a/pytransform3d/visualizer/_artists.py b/pytransform3d/visualizer/_artists.py
index 37ad3a212..3c62c437b 100644
--- a/pytransform3d/visualizer/_artists.py
+++ b/pytransform3d/visualizer/_artists.py
@@ -6,6 +6,7 @@
 from .. import rotations as pr
 from .. import transformations as pt
 from .. import urdf
+from .. import mesh_loader
 
 
 class Artist:
@@ -554,27 +555,8 @@ class Mesh(Artist):
     """
     def __init__(self, filename, A2B=np.eye(4), s=np.ones(3), c=None,
                  convex_hull=False):
-        if filename.endswith(".dae"):
-            import collada
-            mesh = o3d.geometry.TriangleMesh()
-            try:
-                model = collada.Collada(filename)
-                for geometry in model.geometries:
-                    for primitive in geometry.primitives:
-                        p = o3d.geometry.TriangleMesh()
-                        vertices = primitive.vertex
-                        p.vertices = o3d.utility.Vector3dVector(vertices)
-                        triangles = primitive.vertex_index
-                        p.triangles = o3d.utility.Vector3iVector(triangles)
-                        mesh += p
-            except:
-                warnings.warn("Parsing collada file '%s' failed" % filename)
-        else:
-            mesh = o3d.io.read_triangle_mesh(filename)
-        if convex_hull:
-            self.mesh = mesh.compute_convex_hull()[0]
-        else:
-            self.mesh = mesh
+        self.mesh = mesh_loader.load_mesh(
+            filename, convex_hull=convex_hull, return_as_open3d_mesh=True)
         self.mesh.vertices = o3d.utility.Vector3dVector(
             np.asarray(self.mesh.vertices) * s)
         self.mesh.compute_vertex_normals()

From 6bdbe760bfbb060d99645cf7dd14fbc0ea1e5e47 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 11:52:24 +0200
Subject: [PATCH 03/15] Use new trimesh API

---
 pytransform3d/mesh_loader.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 079f96c09..6f2afad01 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -12,8 +12,7 @@ def load_mesh(filename, convex_hull=False, return_as_open3d_mesh=False):
         done = True
 
         if isinstance(geometry, trimesh.Scene):
-            geometry = trimesh.util.concatenate(
-                list(geometry.geometry.values()))
+            geometry = geometry.dump().sum()
         if convex_hull:
             geometry = geometry.convex_hull
 

From 445cb5c082a96df23abff3f59ef1e96aa7348438 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:07:04 +0200
Subject: [PATCH 04/15] Use object interface

---
 pytransform3d/mesh_loader.py                | 168 +++++++++++++++-----
 pytransform3d/plot_utils/_plot_functions.py |   6 +-
 pytransform3d/visualizer/_artists.py        |   4 +-
 3 files changed, 137 insertions(+), 41 deletions(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 6f2afad01..1b3cfe59d 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -1,49 +1,145 @@
+import abc
+
 import numpy as np
 
 
-def load_mesh(filename, convex_hull=False, return_as_open3d_mesh=False):
-    vertices = np.empty((0, 3), dtype=float)
-    triangles = np.empty((0, 3), dtype=int)
-    done = False
+def load_mesh(filename, convex_hull=False):
+    """Load mesh from file.
 
-    try:
-        import trimesh
-        geometry = trimesh.load(filename)
-        done = True
+    Parameters
+    ----------
+    filename : str
+        File in which the mesh is stored.
 
-        if isinstance(geometry, trimesh.Scene):
-            geometry = geometry.dump().sum()
-        if convex_hull:
-            geometry = geometry.convex_hull
+    convex_hull : bool, optional (default: False)
+        Compute convex hull of mesh.
 
-        vertices = geometry.vertices
-        triangles = geometry.faces
+    Returns
+    -------
+    mesh : MeshBase
+        Mesh instance.
+    """
+    mesh = _Trimesh(filename)
+    success = mesh.load()
 
-        if return_as_open3d_mesh:
-            import open3d
-            return open3d.geometry.TriangleMesh(
-                open3d.utility.Vector3dVector(vertices),
-                open3d.utility.Vector3iVector(triangles))
-    except ImportError:
-        pass
+    if not success:
+        mesh = _Open3DMesh(filename)
+        success = mesh.load()
+
+    if not success:
+        raise IOError("Could not load mesh from '%s'" % filename)
+
+    if convex_hull:
+        mesh.convex_hull()
+
+    return mesh
+
+
+class MeshBase(abc.ABC):
+    """Abstract base class of meshes.
+
+    Parameters
+    ----------
+    filename : str
+        File in which the mesh is stored.
+    """
+    def __init__(self, filename):
+        self.filename = filename
+
+    @abc.abstractmethod
+    def load(self):
+        """Load mesh from file.
+
+        Returns
+        -------
+        success : bool
+            Has the mesh been loaded?
+        """
+
+    @abc.abstractmethod
+    def convex_hull(self):
+        """Compute convex hull of mesh."""
+
+    @abc.abstractmethod
+    def get_open3d_mesh(self):
+        """Return Open3D mesh.
+
+        Returns
+        -------
+        mesh : open3d.geometry.TriangleMesh
+            Open3D mesh.
+        """
 
-    try:
+    @property
+    @abc.abstractmethod
+    def vertices(self):
+        """Vertices."""
+
+    @property
+    @abc.abstractmethod
+    def triangles(self):
+        """Triangles."""
+
+
+class _Trimesh(MeshBase):
+    def __init__(self, filename):
+        super(_Trimesh, self).__init__(filename)
+        self.mesh = None
+
+    def load(self):
+        try:
+            import trimesh
+        except ImportError:
+            return False
+
+        obj = trimesh.load(self.filename)
+        if isinstance(obj, trimesh.Scene):
+            obj = obj.dump().sum()
+        self.mesh = obj
+        return True
+
+    def convex_hull(self):
+        self.mesh = self.mesh.convex_hull
+
+    def get_open3d_mesh(self):
         import open3d
-        mesh = open3d.io.read_triangle_mesh(filename)
-        done = True
+        return open3d.geometry.TriangleMesh(
+            open3d.utility.Vector3dVector(self.vertices),
+            open3d.utility.Vector3iVector(self.triangles))
 
-        if convex_hull:
-            mesh = mesh.compute_convex_hull()[0]
+    @property
+    def vertices(self):
+        return self.mesh.vertices
 
-        if return_as_open3d_mesh:
-            return mesh
-        else:
-            vertices = np.asarray(mesh.vertices)
-            triangles = np.asarray(mesh.triangles)
-    except ImportError:
-        pass
+    @property
+    def triangles(self):
+        return self.mesh.faces
 
-    if not done:
-        raise IOError("Could not load mesh from '%s'" % filename)
 
-    return vertices, triangles
+class _Open3DMesh(MeshBase):
+    def __init__(self, filename):
+        super(_Open3DMesh, self).__init__(filename)
+        self.mesh = None
+
+    def load(self):
+        try:
+            import open3d
+        except ImportError:
+            return False
+        self.mesh = open3d.io.read_triangle_mesh(self.filename)
+        return True
+
+    def convex_hull(self):
+        assert self.mesh is not None
+        self.mesh = self.mesh.compute_convex_hull()[0]
+
+    def get_open3d_mesh(self):
+        return self.mesh
+
+    @property
+    def vertices(self):
+        return np.asarray(self.mesh.vertices)
+
+    @property
+    def triangles(self):
+        return np.asarray(self.mesh.triangles)
diff --git a/pytransform3d/plot_utils/_plot_functions.py b/pytransform3d/plot_utils/_plot_functions.py
index ea4bb709e..c81f2ca3c 100644
--- a/pytransform3d/plot_utils/_plot_functions.py
+++ b/pytransform3d/plot_utils/_plot_functions.py
@@ -365,11 +365,11 @@ def plot_mesh(ax=None, filename=None, A2B=np.eye(4),
             "package directory.")
         return ax
 
-    vertices, triangles = load_mesh(filename, convex_hull=convex_hull)
-    vertices = vertices * s
+    mesh = load_mesh(filename, convex_hull=convex_hull)
+    vertices = mesh.vertices * s
     vertices = np.hstack((vertices, np.ones((len(vertices), 1))))
     vertices = transform(A2B, vertices)[:, :3]
-    vectors = np.array([vertices[[i, j, k]] for i, j, k in triangles])
+    vectors = np.array([vertices[[i, j, k]] for i, j, k in mesh.triangles])
     if wireframe:
         surface = Line3DCollection(vectors)
         surface.set_color(color)
diff --git a/pytransform3d/visualizer/_artists.py b/pytransform3d/visualizer/_artists.py
index 3c62c437b..b675cfd01 100644
--- a/pytransform3d/visualizer/_artists.py
+++ b/pytransform3d/visualizer/_artists.py
@@ -555,8 +555,8 @@ class Mesh(Artist):
     """
     def __init__(self, filename, A2B=np.eye(4), s=np.ones(3), c=None,
                  convex_hull=False):
-        self.mesh = mesh_loader.load_mesh(
-            filename, convex_hull=convex_hull, return_as_open3d_mesh=True)
+        mesh = mesh_loader.load_mesh(filename, convex_hull=convex_hull)
+        self.mesh = mesh.get_open3d_mesh()
         self.mesh.vertices = o3d.utility.Vector3dVector(
             np.asarray(self.mesh.vertices) * s)
         self.mesh.compute_vertex_normals()

From 84754b0d1cc7174417a7c6669f9f40be0fe46257 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:09:23 +0200
Subject: [PATCH 05/15] Add pycollada to all dependencies

---
 setup.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/setup.py b/setup.py
index c380cc6db..a3a5e695d 100644
--- a/setup.py
+++ b/setup.py
@@ -26,7 +26,7 @@
           packages=find_packages(),
           install_requires=["numpy", "scipy", "matplotlib", "lxml"],
           extras_require={
-              "all": ["pydot", "trimesh", "open3d"],
+              "all": ["pydot", "trimesh", "pycollada", "open3d"],
               "doc": ["numpydoc", "sphinx", "sphinx-gallery",
                       "sphinx-bootstrap-theme"],
               "test": ["pytest", "pytest-cov"]

From f44d61561123c7bb7f061cf8a561e392a5710101 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:12:29 +0200
Subject: [PATCH 06/15] Add docstring

---
 pytransform3d/mesh_loader.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 1b3cfe59d..77936292f 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -6,6 +6,12 @@
 def load_mesh(filename, convex_hull=False):
     """Load mesh from file.
 
+    This feature relies on optional dependencies. It can use trimesh or
+    Open3D to load meshes. If both are not available, it will fail.
+    Furthermore, some mesh formats require additional dependencies. For
+    example, loading collada files ('.dae' file ending) requires pycollada
+    and trimesh.
+
     Parameters
     ----------
     filename : str

From 07502b97ff89bfd869fa602f661c339b72e4e3cf Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:17:21 +0200
Subject: [PATCH 07/15] Change loader interface

---
 pytransform3d/mesh_loader.py                | 25 +++++++++------------
 pytransform3d/plot_utils/_plot_functions.py |  5 ++++-
 pytransform3d/visualizer/_artists.py        |  5 ++++-
 3 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 77936292f..43c162500 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -3,7 +3,7 @@
 import numpy as np
 
 
-def load_mesh(filename, convex_hull=False):
+def load_mesh(filename):
     """Load mesh from file.
 
     This feature relies on optional dependencies. It can use trimesh or
@@ -17,26 +17,22 @@ def load_mesh(filename, convex_hull=False):
     filename : str
         File in which the mesh is stored.
 
-    convex_hull : bool, optional (default: False)
-        Compute convex hull of mesh.
-
     Returns
     -------
     mesh : MeshBase
         Mesh instance.
     """
     mesh = _Trimesh(filename)
-    success = mesh.load()
+    loader_available = mesh.load()
 
-    if not success:
+    if not loader_available:
         mesh = _Open3DMesh(filename)
-        success = mesh.load()
-
-    if not success:
-        raise IOError("Could not load mesh from '%s'" % filename)
+        loader_available = mesh.load()
 
-    if convex_hull:
-        mesh.convex_hull()
+    if not loader_available:
+        raise IOError(
+            "Could not load mesh from '%s'. Please install one of the "
+            "optional dependencies 'trimesh' or 'open3d'." % filename)
 
     return mesh
 
@@ -58,8 +54,8 @@ def load(self):
 
         Returns
         -------
-        success : bool
-            Has the mesh been loaded?
+        loader_available : bool
+            Is the mesh loader available?
         """
 
     @abc.abstractmethod
@@ -97,7 +93,6 @@ def load(self):
             import trimesh
         except ImportError:
             return False
-
         obj = trimesh.load(self.filename)
         if isinstance(obj, trimesh.Scene):
             obj = obj.dump().sum()
diff --git a/pytransform3d/plot_utils/_plot_functions.py b/pytransform3d/plot_utils/_plot_functions.py
index c81f2ca3c..9ce1a5c87 100644
--- a/pytransform3d/plot_utils/_plot_functions.py
+++ b/pytransform3d/plot_utils/_plot_functions.py
@@ -365,7 +365,10 @@ def plot_mesh(ax=None, filename=None, A2B=np.eye(4),
             "package directory.")
         return ax
 
-    mesh = load_mesh(filename, convex_hull=convex_hull)
+    mesh = load_mesh(filename)
+    if convex_hull:
+        mesh.convex_hull()
+
     vertices = mesh.vertices * s
     vertices = np.hstack((vertices, np.ones((len(vertices), 1))))
     vertices = transform(A2B, vertices)[:, :3]
diff --git a/pytransform3d/visualizer/_artists.py b/pytransform3d/visualizer/_artists.py
index b675cfd01..6219d6098 100644
--- a/pytransform3d/visualizer/_artists.py
+++ b/pytransform3d/visualizer/_artists.py
@@ -555,7 +555,10 @@ class Mesh(Artist):
     """
     def __init__(self, filename, A2B=np.eye(4), s=np.ones(3), c=None,
                  convex_hull=False):
-        mesh = mesh_loader.load_mesh(filename, convex_hull=convex_hull)
+        mesh = mesh_loader.load_mesh(filename)
+        if convex_hull:
+            mesh.convex_hull()
+
         self.mesh = mesh.get_open3d_mesh()
         self.mesh.vertices = o3d.utility.Vector3dVector(
             np.asarray(self.mesh.vertices) * s)

From dad23560c088e62c97503b4baa08f10002ddbc7d Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:32:45 +0200
Subject: [PATCH 08/15] Add type stub

---
 pytransform3d/mesh_loader.pyi | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 pytransform3d/mesh_loader.pyi

diff --git a/pytransform3d/mesh_loader.pyi b/pytransform3d/mesh_loader.pyi
new file mode 100644
index 000000000..3eab08060
--- /dev/null
+++ b/pytransform3d/mesh_loader.pyi
@@ -0,0 +1,30 @@
+import abc
+from typing import Any
+
+import numpy.typing as npt
+
+
+class MeshBase(abc.ABC):
+    filename: str
+
+    def __init__(self, filename: str): ...
+
+    @abc.abstractmethod
+    def load(self) -> bool: ...
+
+    @abc.abstractmethod
+    def convex_hull(self): ...
+
+    @abc.abstractmethod
+    def get_open3d_mesh(self) -> Any: ...
+
+    @property
+    @abc.abstractmethod
+    def vertices(self) -> npt.ArrayLike: ...
+
+    @property
+    @abc.abstractmethod
+    def triangles(self) -> npt.ArrayLike: ...
+
+
+def load_mesh(filename: str) -> MeshBase: ...

From 7147c206b8b52f44e9bb9cdda6ed0c5563be4dea Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:50:10 +0200
Subject: [PATCH 09/15] Test mesh loader

---
 pytransform3d/mesh_loader.py           |  4 +-
 pytransform3d/test/test_mesh_loader.py | 54 ++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 pytransform3d/test/test_mesh_loader.py

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 43c162500..bdb8f5371 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -29,8 +29,8 @@ def load_mesh(filename):
         mesh = _Open3DMesh(filename)
         loader_available = mesh.load()
 
-    if not loader_available:
-        raise IOError(
+    if not loader_available:  # pragma: no cover
+        raise ImportError(
             "Could not load mesh from '%s'. Please install one of the "
             "optional dependencies 'trimesh' or 'open3d'." % filename)
 
diff --git a/pytransform3d/test/test_mesh_loader.py b/pytransform3d/test/test_mesh_loader.py
new file mode 100644
index 000000000..59395831d
--- /dev/null
+++ b/pytransform3d/test/test_mesh_loader.py
@@ -0,0 +1,54 @@
+from pytransform3d import mesh_loader
+
+import pytest
+
+
+def test_trimesh():
+    mesh = mesh_loader._Trimesh("test/test_data/cone.stl")
+    loader_available = mesh.load()
+    if not loader_available:
+        pytest.skip("trimesh is required for this test")
+
+    assert len(mesh.vertices) == 64
+    assert len(mesh.triangles) == 124
+
+    mesh.convex_hull()
+
+    assert len(mesh.vertices) == 64
+
+
+def test_open3d():
+    mesh = mesh_loader._Open3DMesh("test/test_data/cone.stl")
+    loader_available = mesh.load()
+    if not loader_available:
+        pytest.skip("open3d is required for this test")
+
+    assert len(mesh.vertices) == 295
+    assert len(mesh.triangles) == 124
+
+    o3d_mesh = mesh.get_open3d_mesh()
+    assert len(o3d_mesh.vertices) == 295
+
+    mesh.convex_hull()
+
+    assert len(mesh.vertices) == 64
+
+
+def test_trimesh_with_open3d():
+    mesh = mesh_loader._Trimesh("test/test_data/cone.stl")
+    loader_available = mesh.load()
+    if not loader_available:
+        pytest.skip("trimesh is required for this test")
+    try:
+        o3d_mesh = mesh.get_open3d_mesh()
+    except ImportError:
+        pytest.skip("open3d is required for this test")
+    assert len(o3d_mesh.vertices) == 64
+
+
+def test_interface():
+    try:
+        mesh = mesh_loader.load_mesh("test/test_data/cone.stl")
+        assert len(mesh.triangles) == 124
+    except ImportError:
+        pytest.skip("trimesh or open3d are required for this test")

From 39d8c5a9346445933ded9dec6a6838473636ddd1 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 15:56:06 +0200
Subject: [PATCH 10/15] Fix coverage

---
 pytransform3d/mesh_loader.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index bdb8f5371..83b4df767 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -25,7 +25,7 @@ def load_mesh(filename):
     mesh = _Trimesh(filename)
     loader_available = mesh.load()
 
-    if not loader_available:
+    if not loader_available:  # pragma: no cover
         mesh = _Open3DMesh(filename)
         loader_available = mesh.load()
 

From 75761bc0f2f037286901750d2bd9711dab6ae30a Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 16:04:05 +0200
Subject: [PATCH 11/15] Increase coverage

---
 pytransform3d/mesh_loader.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 83b4df767..69dc850e8 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -94,7 +94,10 @@ def load(self):
         except ImportError:
             return False
         obj = trimesh.load(self.filename)
-        if isinstance(obj, trimesh.Scene):
+        if isinstance(obj, trimesh.Scene):  # pragma: no cover
+            # Special case in which we load a collada file that contains
+            # multiple meshes. We might lose textures. This is excluded
+            # from testing as it would add another dependency.
             obj = obj.dump().sum()
         self.mesh = obj
         return True

From e52031aeda9bf02776c0e8b1517dcd4d1f26835c Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 16:06:51 +0200
Subject: [PATCH 12/15] Exclude Open3D mesh loader from coverage

---
 pytransform3d/mesh_loader.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 69dc850e8..42a4c5b16 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -120,7 +120,7 @@ def triangles(self):
         return self.mesh.faces
 
 
-class _Open3DMesh(MeshBase):
+class _Open3DMesh(MeshBase):  # pragma: no cover
     def __init__(self, filename):
         super(_Open3DMesh, self).__init__(filename)
         self.mesh = None

From 1abe18590b191339c80b32aef0723c18db81883b Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 16:09:13 +0200
Subject: [PATCH 13/15] Exclude open3d from coverage

---
 pytransform3d/mesh_loader.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 42a4c5b16..834383dbf 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -105,7 +105,7 @@ def load(self):
     def convex_hull(self):
         self.mesh = self.mesh.convex_hull
 
-    def get_open3d_mesh(self):
+    def get_open3d_mesh(self):  # pragma: no cover
         import open3d
         return open3d.geometry.TriangleMesh(
             open3d.utility.Vector3dVector(self.vertices),

From 87ae696f87fd9afda57ee4966385a13cd6e5e106 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Thu, 27 Jul 2023 16:11:22 +0200
Subject: [PATCH 14/15] Add module docstring

---
 pytransform3d/mesh_loader.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pytransform3d/mesh_loader.py b/pytransform3d/mesh_loader.py
index 834383dbf..b42a26330 100644
--- a/pytransform3d/mesh_loader.py
+++ b/pytransform3d/mesh_loader.py
@@ -1,3 +1,4 @@
+"""Common interface to load meshes."""
 import abc
 
 import numpy as np

From f082bff544c46a29154731b97e3571813f51ab15 Mon Sep 17 00:00:00 2001
From: Alexander Fabisch <alexander.fabisch@dfki.de>
Date: Fri, 28 Jul 2023 11:20:07 +0200
Subject: [PATCH 15/15] Add pycollada to requirements.txt

---
 requirements.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/requirements.txt b/requirements.txt
index ba9132165..85caf81c7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,5 +3,6 @@ scipy
 matplotlib
 lxml
 trimesh
+pycollada
 pydot
 open3d