在open3d中创建箭头

Question

我正在使用Open3D来可视化一些点云。我想添加箭头，开始和结束在特定的点。箭头可以想象出我正在做的一些事情。但是，我没有找到一个简单的方法来添加这些箭头。在

我注意到有一个函数可以创建笛卡尔坐标系，它使用箭头。因此，可以在三维可视化中添加箭头。在

import open3d as o3d
# Create cartesian coordinate 
FOR = o3d.geometry.TriangleMesh.create_coordinate_frame(
    size=10, origin=[0,0,0])
# Visualize FOR
o3d.visualization.draw_geometries([FOR])

Answer 1

在Open3D中没有找到一种简单的方法来创建箭头，这让我很沮丧，经过一段时间的努力，我想出了一个解决方案。在

import open3d as o3d
import numpy as np

def draw_geometries(pcds):
    """
    Draw Geometries
    Args:
        - pcds (): [pcd1,pcd2,...]
    """
    o3d.visualization.draw_geometries(pcds)

def get_o3d_FOR(origin=[0, 0, 0],size=10):
    """ 
    Create a FOR that can be added to the open3d point cloud
    """
    mesh_frame = o3d.geometry.TriangleMesh.create_coordinate_frame(
    size=size, origin=origin)
    return(mesh_frame)

def vector_magnitude(vec):
    """
    Calculates a vector's magnitude.
    Args:
        - vec (): 
    """
    magnitude = np.sqrt(np.sum(vec**2))
    return(magnitude)


def calculate_zy_rotation_for_arrow(vec):
    """
    Calculates the rotations required to go from the vector vec to the 
    z axis vector of the original FOR. The first rotation that is 
    calculated is over the z axis. This will leave the vector vec on the
    XZ plane. Then, the rotation over the y axis. 

    Returns the angles of rotation over axis z and y required to
    get the vector vec into the same orientation as axis z
    of the original FOR

    Args:
        - vec (): 
    """
    # Rotation over z axis of the FOR
    gamma = np.arctan(vec[1]/vec[0])
    Rz = np.array([[np.cos(gamma),-np.sin(gamma),0],
                   [np.sin(gamma),np.cos(gamma),0],
                   [0,0,1]])
    # Rotate vec to calculate next rotation
    vec = Rz.T@vec.reshape(-1,1)
    vec = vec.reshape(-1)
    # Rotation over y axis of the FOR
    beta = np.arctan(vec[0]/vec[2])
    Ry = np.array([[np.cos(beta),0,np.sin(beta)],
                   [0,1,0],
                   [-np.sin(beta),0,np.cos(beta)]])
    return(gamma,beta)

def create_arrow(scale=10):
    """
    Create an arrow in for Open3D
    """
    cone_height = scale*0.2
    cylinder_height = scale*0.8
    cone_radius = scale/10
    cylinder_radius = scale/20
    mesh_frame = o3d.geometry.TriangleMesh.create_arrow(cone_radius=1,
        cone_height=cone_height,
        cylinder_radius=0.5,
        cylinder_height=cylinder_height)
    return(mesh_frame)

def get_arrow(origin=[0,0,0],end=None,vec=None):
    """
    Creates an arrow from an origin point to an end point,
    or create an arrow from a vector vec starting from origin.
    Args:
        - end (): End point. [x,y,z]
        - vec (): Vector. [i,j,k]
    """
    scale = 10; beta = 0; gamma = 0
    T = np.array([[1,0,0,0],[0,1,0,0],[0,0,1,0],[0,0,0,1]])
    T[:3,-1] = origin
    if end is not None:
        vec = np.array(end) - np.array(origin)
    elif vec is not None:
        vec = np.array(vec)
    if end is not None or vec is not None:
        scale = vector_magnitude(vec)
        gamma,beta = calculate_zy_rotation_for_arrow(vec)
    mesh = create_arrow(scale)
    # mesh.transform(T)
    mesh.rotate([0,beta,0],center=False)
    mesh.rotate([0,0,gamma],center=False)
    mesh.translate(origin)
    return(mesh)


# Create a Cartesian Frame of Reference
FOR = get_o3d_FOR()
# Create an arrow from point (5,5,5) to point (10,10,10)
# arrow = get_arrow([5,5,5],[10,10,10])

# Create an arrow representing vector vec, starting at (5,5,5)
# arrow = get_arrow([5,5,5],vec=[5,5,5])

# Create an arrow in the same place as the z axis
arrow = get_arrow()

# Draw everything
draw_geometries([FOR,arrow])