RaycastingScene class in Open3D provides basic ray casting functionality. In this tutorial we show how to create a scene and do ray intersection tests. You can also use
RaycastingScene to create a virtual point cloud from a mesh, such as from a CAD model.
As the first step we initialize a
RaycastingScene with one or more triangle meshes.
# Load mesh and convert to open3d.t.geometry.TriangleMesh cube = o3d.geometry.TriangleMesh.create_box().translate([0, 0, 0]) cube = o3d.t.geometry.TriangleMesh.from_legacy(cube)
# Create a scene and add the triangle mesh scene = o3d.t.geometry.RaycastingScene() cube_id = scene.add_triangles(cube)
add_triangles() returns the ID for the added geometry. This ID can be used to identify which mesh is hit by a ray.
We can now generate rays which are 6D vectors with origin and direction.
# We create two rays: # The first ray starts at (0.5,0.5,10) and has direction (0,0,-1). # The second ray start at (-1,-1,-1) and has direction (0,0,-1). rays = o3d.core.Tensor([[0.5, 0.5, 10, 0, 0, -1], [-1, -1, -1, 0, 0, -1]], dtype=o3d.core.Dtype.Float32) ans = scene.cast_rays(rays)
The result contains information about a possible intersection with the geometry in the scene.
dict_keys(['primitive_uvs', 'primitive_ids', 'geometry_ids', 'primitive_normals', 't_hit'])
t_hit is the distance to the intersection. The unit is defined by the length of the ray direction. If there is no intersection this is inf
geometry_ids gives the id of the geometry hit by the ray. If no geometry was hit this is
primitive_ids is the triangle index of the triangle that was hit or
primitive_uvs is the barycentric coordinates of the intersection point within the triangle.
primitive_normals is the normal of the hit triangle.
We can see from t_hit and geometry_ids that the first ray did hit the mesh but the second ray missed.
[8.999999 inf] [ 0 4294967295]
We now create a scene with multiple objects
# Create meshes and convert to open3d.t.geometry.TriangleMesh cube = o3d.geometry.TriangleMesh.create_box().translate([0, 0, 0]) cube = o3d.t.geometry.TriangleMesh.from_legacy(cube) torus = o3d.geometry.TriangleMesh.create_torus().translate([0, 0, 2]) torus = o3d.t.geometry.TriangleMesh.from_legacy(torus) sphere = o3d.geometry.TriangleMesh.create_sphere(radius=0.5).translate( [1, 2, 3]) sphere = o3d.t.geometry.TriangleMesh.from_legacy(sphere) scene = o3d.t.geometry.RaycastingScene() scene.add_triangles(cube) scene.add_triangles(torus) _ = scene.add_triangles(sphere)
RaycastingScene allows to organize rays with an arbitrary number of leading dimensions. For instance we can generate an array with shape
[h,w,6] to organize rays for creating an image. The class also provides helper functions for creating rays for a pinhole camera. The following creates rays Tensor with shape
rays = o3d.t.geometry.RaycastingScene.create_rays_pinhole( fov_deg=90, center=[0, 0, 2], eye=[2, 3, 0], up=[0, 1, 0], width_px=640, height_px=480, ) # We can directly pass the rays tensor to the cast_rays function. ans = scene.cast_rays(rays)
The output tensors preserve the shape of the rays and we can directly visualize the hit distance with matplotlib to get a depth map.
import matplotlib.pyplot as plt plt.imshow(ans['t_hit'].numpy())
<matplotlib.image.AxesImage at 0x7ff6d05fa2b0>
Furhter we can plot the other results to visualize the primitive normals, ..
# use abs to avoid negative values plt.imshow(np.abs(ans['primitive_normals'].numpy()))
<matplotlib.image.AxesImage at 0x7ff6d016f860>
<matplotlib.image.AxesImage at 0x7ff6d0520748>
Creating a virtual point cloud¶
We can also use the hit distance to calculate the XYZ coordinates of the intersection points. These are the points that you would get by placing a virtual 3D sensor at the point of origin of the rays.
hit = ans['t_hit'].isfinite() points = rays[hit][:,:3] + rays[hit][:,3:]*ans['t_hit'][hit].reshape((-1,1)) pcd = o3d.t.geometry.PointCloud(points) # Press Ctrl/Cmd-C in the visualization window to copy the current viewpoint o3d.visualization.draw_geometries([pcd.to_legacy()], front=[0.5, 0.86, 0.125], lookat=[0.23, 0.5, 2], up=[-0.63, 0.45, -0.63], zoom=0.7) # o3d.visualization.draw([pcd]) # new API