【小白深度教程 1.13】手把手教你使用 Open3D，简明教程（含 Python 代码）

Open3D是一个开源库，支持处理3D数据的软件的 快速开发

它是由英特尔实验室的研究人员周乾一、Jaesik Park和Vladlen Koltun 开发的，这是对应的论文：

http://www.open3d.org/wordpress/wp-content/paper.pdf

1. 创建环境

conda create -n open3denv python=3.6
conda activate open3denv
conda install -c open3d-admin open3d==0.8.0.0
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2. 下载数据集

http ://graphics.stanford.edu/data/3Dscanrep/

3. 加载点云数据

import open3d as o3d
import wget
url = 'https://raw.githubusercontent.com/PointCloudLibrary/pcl/master/test/bunny.pcd'
#filename = wget.download(url)

pcd = o3d.io.read_point_cloud("bunny.pcd")
print(pcd)
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4. Open3D 文件点云文件格式

#The code below writes a point cloud.
o3d.io.write_point_cloud("copy_of_bunny.pcd", pcd)
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pcd = o3d.io.read_point_cloud("sample.xyz", format='xyz')
print(pcd)
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5. Open3D 文件 Mesh 文件格式

# The code below reads and writes a mesh.
print("Testing IO for meshes ...")

#Function to read TriangleMesh from file
mesh = o3d.io.read_triangle_mesh("knot.ply")
print(mesh)
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6. 在样例数据使用 Open3D

6.1 Bunny 数据集

import open3d as o3d
import numpy as np
import PIL.Image
import IPython.display
import os
import urllib
import tarfile
import gzip
import zipfile
import shutil

#Download the point cloud using below command
import wget
url = 'http://graphics.stanford.edu/pub/3Dscanrep/bunny.tar.gz'
#filename = wget.download(url)

bunny_path = "bunny"
with tarfile.open(bunny_path + ".tar.gz") as tar:
            tar.extractall(path=os.path.dirname(bunny_path))

bunny_path = "D:/open3D_env/bunny/reconstruction/bun_zipper.ply"
mesh = o3d.io.read_triangle_mesh(bunny_path)
mesh.compute_vertex_normals()

mesh.compute_vertex_normals()
o3d.visualization.draw_geometries([mesh])

pcd = mesh.sample_points_uniformly(number_of_points=500)
o3d.visualization.draw_geometries([pcd])
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6.2 Happy Buddha 数据集

#Download the Happy Buddha dataset
import wget
url = 'http://graphics.stanford.edu/pub/3Dscanrep/happy/happy_recon.tar.gz'
#filename = wget.download(url)

budha_path = "happy_recon"
with tarfile.open(budha_path + ".tar.gz") as tar:
            tar.extractall(path=os.path.dirname(budha_path))
        
budha_path = "D:/open3D_env/happy_recon/happy_vrip.ply"
mesh_budha = o3d.io.read_triangle_mesh(budha_path)
mesh_budha.compute_vertex_normals()

mesh_budha.compute_vertex_normals()
o3d.visualization.draw_geometries([mesh_budha])

pcd_budha = mesh_budha.sample_points_uniformly(number_of_points=500)
o3d.visualization.draw_geometries([pcd_budha])
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6.3 Dragon 数据集

import wget
url = 'http://graphics.stanford.edu/pub/3Dscanrep/dragon/dragon_recon.tar.gz'
#filename = wget.download(url)

dragon_path = "dragon_recon"
with tarfile.open(dragon_path + ".tar.gz") as tar:
            tar.extractall(path=os.path.dirname(dragon_path))
        
dragon_path = "D:/open3D_env/dragon_recon/dragon_vrip.ply"
mesh_dragon = o3d.io.read_triangle_mesh(dragon_path)
mesh_dragon.compute_vertex_normals()

mesh_dragon.compute_vertex_normals()
o3d.visualization.draw_geometries([mesh_dragon])

pcd_dragon = mesh_dragon.sample_points_uniformly(number_of_points=500)
o3d.visualization.draw_geometries([pcd_dragon])
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7. 体素降采样

1. 这是点云处理任务的预处理步骤。
2. 它取点云和下采样。
3. 在1体素中的点被平均，平均后我们得到1点。

为什么要降采样？

• 它使数据的大小更易于管理

• 降低数据的维数，从而实现更快的数据处理

• 减少数据的存储大小

print("Downsample the point cloud with a voxel of 0.05")
downpcd = pcd_dragon.voxel_down_sample(voxel_size=0.05)
o3d.visualization.draw_geometries([downpcd],width=1920, height=1080, left=50, top=50)
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另一种实现方式：

import numpy as np
print("Load a ply point cloud, print it, and render it")

#read_point_cloud reads a point cloud from a file. It tries to decode the file based on the extension name.
pcd = o3d.io.read_point_cloud("fragment.ply")
print(pcd)
print(np.asarray(pcd.points))

#draw_geometries visualizes the point cloud. 
o3d.visualization.draw_geometries([pcd],width=1920, height=1080, left=50, top=50)
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print("Downsample the point cloud with a voxel of 0.05")
downpcd = pcd.voxel_down_sample(voxel_size=0.05)
o3d.visualization.draw_geometries([downpcd],width=1920, height=1080, left=50, top=50)
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8. 裁剪点云

print("Load a polygon volume and use it to crop the original point cloud")

#read_selection_polygon_volume reads a json file that specifies polygon selection area. 
vol = o3d.visualization.read_selection_polygon_volume("cropped.json")

#vol.crop_point_cloud(pcd) filters out points. Only the chair remains.
chair = vol.crop_point_cloud(pcd)
o3d.visualization.draw_geometries([chair],width=1920, height=1080, left=50, top=50)
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加载一个模型，并使用它来裁剪原始点云

9. 点云着色

print("Paint chair")

#paint_uniform_color paints all the points to a uniform color. The color is in RGB space, [0, 1] range.
chair.paint_uniform_color([1, 0.706, 0])
o3d.visualization.draw_geometries([chair], width=1920, height=1080, left=50, top=50)
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10. 绘制矩形 框

PointCloud几何类型与Open3D中的所有其他几何类型一样具有边界框。

目前，Open3D实现了一个AxisAlignedBoundingBox和一个orientteddboundingbox，它们也可以用来裁剪几何图形。

aabb = chair.get_axis_aligned_bounding_box()
aabb.color = (1, 0, 0)
obb = chair.get_oriented_bounding_box()
obb.color = (0, 1, 0)
o3d.visualization.draw_geometries([chair, aabb, obb])
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11. Mesh 处理

Open3D有一个3D三角形网格的数据结构，叫做TriangleMesh。下面的代码展示了如何从ply文件中读取三角形网格并打印其顶点和三角形。

#!pip install pillow

# import functions from open3d_tutorial.py 
import open3d_tutorial as o3dtut


print("Testing mesh in Open3D...")
mesh = o3dtut.get_knot_mesh()
print(mesh)
print('Vertices:')
print(np.asarray(mesh.vertices))
print('Triangles:')
print(np.asarray(mesh.triangles))

#The TriangleMesh class has a few data fields such as vertices and triangles. Open3D provides direct memory access to these fields via numpy.

print("Try to render a mesh with normals (exist: " +str(mesh.has_vertex_normals()) + ") and colors (exist: " +str(mesh.has_vertex_colors()) + ")")
o3d.visualization.draw_geometries([mesh])
print("A mesh with no normals and no colors does not look good.")
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print("Computing normal and rendering it.")
mesh.compute_vertex_normals()
print(np.asarray(mesh.triangle_normals))
o3d.visualization.draw_geometries([mesh])
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12. 裁剪 Mesh

我们通过直接操作网格的triangle和triangle_normals数据字段来去除一半的表面。这是通过 numpy 完成的。

print("We make a partial mesh of only the first half triangles.")
#mesh1 = copy.deepcopy(mesh)
mesh1=mesh
mesh1.triangles = o3d.utility.Vector3iVector(
    np.asarray(mesh1.triangles)[:len(mesh1.triangles) // 2, :])
mesh1.triangle_normals = o3d.utility.Vector3dVector(
    np.asarray(mesh1.triangle_normals)[:len(mesh1.triangle_normals) // 2, :])
print(mesh1.triangles)
o3d.visualization.draw_geometries([mesh1])
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13. Mesh 着色

Paint_uniform_color用统一的颜色绘制网格。颜色在RGB空间，[0,1]范围内。

print("Painting the mesh")
mesh1.paint_uniform_color([1, 0.706, 0])
o3d.visualization.draw_geometries([mesh1])
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