本文介绍在3D目标检测中，理解和使用KITTI 数据集，包括KITTI 的基本情况、下载数据集、标签格式解析、3D框可视化、点云转图像、画BEV鸟瞰图等，并配有实现代码。
2、KITTI 3D数据集
kitti 3D数据集的基本情况：
KITTI整个数据集是在德国卡尔斯鲁厄采集的，采集时长6小时。KITTI官网放出的数据大约占采集全部的25%，去除了测试集中相关的数据片段，按场景可以分为“道路”、“城市”、“住宅区”、“校园”和“行人”5类。
传感器配置：
传感器安装位置：
3、下载数据集
The KITTI Vision Benchmark Suite (cvlibs.net)
下载数据需要注册账号的，获取取百度网盘下载；文件的格式如下所示
图片格式：xxx.jpg
点云格式：xxx.bin（点云是以bin二进制的方式存储的）
标定参数：xxx.txt（一个文件中包括各个相机的内参、畸变校正矩阵、激光雷达坐标转到相机坐标的矩阵、IMU坐标转到激光雷达坐标的矩阵）
标签格式：xxx.txt（包含类别、截断情况、遮挡情况、观测角度、2D框左上角坐标、2D框右下角坐标、3D物体的尺寸-高宽长、3D物体的中心坐标-xyz、置信度）
4、标签格式
示例标签：Pedestrian 0.00 0 -0.20 712.40 143.00 810.73 307.92 1.89 0.48 1.20 1.84 1.47 8.41 0.01
这时可以看看这个视频：
Nuscenes、KITTI等多个BEV开源数据集介绍
5、标定参数解析
然后看一下标定参数：
P0-P3:是各个相机的内参矩阵；3×4的相机投影矩阵，0~3分别对应左侧灰度相机、右侧灰度相机、左侧彩色相机、右侧彩色相机。
R0_rect: 是左相机的畸变矫正矩阵；3×3的旋转修正矩阵。
Tr_velo_to_cam:是激光雷达坐标系 转到 相机坐标系矩阵；3×4的激光坐标系到Cam 0坐标系的变换矩阵。
Tr_imu_to_velo: 是IMU坐标转到激光雷达坐标的矩阵；3×4的IMU坐标系到激光坐标系的变换矩阵。
6、点云数据-->投影到图像
当有了点云数据信息，如何投影到图像中呢？本质上是一个坐标系转换的问题，流程思路如下：
- 已知点云坐标（x，y，z），当前是处于激光雷达坐标系
- 激光雷达坐标系 转到 相机坐标系，需要用到标定参数中的Tr_velo_to_cam矩阵，此时得到相机坐标（x1，y1，z1）
- 相机坐标系进行畸变矫正，需要用到标定参数中的R0_rect矩阵，此时得到相机坐标（x2，y2，z2）
- 相机坐标系转为图像坐标系，需要用到标定参数中的P0矩阵，即相机内存矩阵，此时得到图像坐标（u，v）
看一下示例效果：
接口代码：
'''
将点云数据投影到图像
'''
def show_lidar_on_image(pc_velo, img, calib, img_width, img_height):
''' Project LiDAR points to image '''
imgfov_pc_velo, pts_2d, fov_inds = get_lidar_in_image_fov(pc_velo,
calib, 0, 0, img_width, img_height, True)
imgfov_pts_2d = pts_2d[fov_inds,:]
imgfov_pc_rect = calib.project_velo_to_rect(imgfov_pc_velo)
import matplotlib.pyplot as plt
cmap = plt.cm.get_cmap('hsv', 256)
cmap = np.array([cmap(i) for i in range(256)])[:,:3]*255
for i in range(imgfov_pts_2d.shape[0]):
depth = imgfov_pc_rect[i,2]
color = cmap[int(640.0/depth),:]
cv2.circle(img, (int(np.round(imgfov_pts_2d[i,0])),
int(np.round(imgfov_pts_2d[i,1]))),
2, color=tuple(color), thickness=-1)
Image.fromarray(img).save('save_output/lidar_on_image.png')
Image.fromarray(img).show()
return img
核心代码：
'''
将点云数据投影到相机坐标系
'''
def get_lidar_in_image_fov(pc_velo, calib, xmin, ymin, xmax, ymax,
return_more=False, clip_distance=2.0):
''' Filter lidar points, keep those in image FOV '''
pts_2d = calib.project_velo_to_image(pc_velo)
fov_inds = (pts_2d[:,0]<xmax) & (pts_2d[:,0]>=xmin) & \
(pts_2d[:,1]<ymax) & (pts_2d[:,1]>=ymin)
fov_inds = fov_inds & (pc_velo[:,0]>clip_distance)
imgfov_pc_velo = pc_velo[fov_inds,:]
if return_more:
return imgfov_pc_velo, pts_2d, fov_inds
else:
return imgfov_pc_velo
7、图像数据-->投影到点云
当有了图像RGB信息，如何投影到点云中呢？本质上是一个坐标系转换的问题，和上面的是逆过程，流程思路如下：
- 已知图像坐标（u，v），当前是处于图像坐标系
- 图像坐标系 转 相机坐标系，需要用到标定参数中的P0逆矩阵，即相机内存矩阵，得到相机坐标（x，y，z）
- 相机坐标系进行畸变矫正，需要用到标定参数中的R0_rect逆矩阵，得到相机坐标（x1，y1，z1）
- 矫正后相机坐标系 转 激光雷达坐标系，需要用到标定参数中的Tr_velo_to_cam逆矩阵，此时得到激光雷达坐标（x2，y2，z2）
8、可视化图像2D结果、3D结果
先看一下2D框的效果：
3D框的效果：
接口代码：
'''
在图像中画2D框、3D框
'''
def show_image_with_boxes(img, objects, calib, show3d=True):
img1 = np.copy(img) # for 2d bbox
img2 = np.copy(img) # for 3d bbox
for obj in objects:
if obj.type=='DontCare':continue
cv2.rectangle(img1, (int(obj.xmin),int(obj.ymin)), (int(obj.xmax),int(obj.ymax)), (0,255,0), 2) # 画2D框
box3d_pts_2d, box3d_pts_3d = utils.compute_box_3d(obj, calib.P) # 获取图像3D框(8*2)、相机坐标系3D框(8*3)
img2 = utils.draw_projected_box3d(img2, box3d_pts_2d) # 在图像上画3D框
if show3d:
Image.fromarray(img2).save('save_output/image_with_3Dboxes.png')
Image.fromarray(img2).show()
else:
Image.fromarray(img1).save('save_output/image_with_2Dboxes.png')
Image.fromarray(img1).show()
核心代码：
def compute_box_3d(obj, P):
'''
计算对象的3D边界框在图像平面上的投影
输入: obj代表一个物体标签信息, P代表相机的投影矩阵-内参。
输出: 返回两个值, corners_3d表示3D边界框在 相机坐标系 的8个角点的坐标-3D坐标。
corners_2d表示3D边界框在 图像上 的8个角点的坐标-2D坐标。
'''
# 计算一个绕Y轴旋转的旋转矩阵R，用于将3D坐标从世界坐标系转换到相机坐标系。obj.ry是对象的偏航角
R = roty(obj.ry)
# 物体实际的长、宽、高
l = obj.l;
w = obj.w;
h = obj.h;
# 存储了3D边界框的8个角点相对于对象中心的坐标。这些坐标定义了3D边界框的形状。
x_corners = [l/2,l/2,-l/2,-l/2,l/2,l/2,-l/2,-l/2];
y_corners = [0,0,0,0,-h,-h,-h,-h];
z_corners = [w/2,-w/2,-w/2,w/2,w/2,-w/2,-w/2,w/2];
# 1、将3D边界框的角点坐标从对象坐标系转换到相机坐标系。它使用了旋转矩阵R
corners_3d = np.dot(R, np.vstack([x_corners,y_corners,z_corners]))
# 3D边界框的坐标进行平移
corners_3d[0,:] = corners_3d[0,:] + obj.t[0];
corners_3d[1,:] = corners_3d[1,:] + obj.t[1];
corners_3d[2,:] = corners_3d[2,:] + obj.t[2];
# 2、检查对象是否在相机前方，因为只有在相机前方的对象才会被绘制。
# 如果对象的Z坐标（深度）小于0.1，就意味着对象在相机后方，那么corners_2d将被设置为None，函数将返回None。
if np.any(corners_3d[2,:]<0.1):
corners_2d = None
return corners_2d, np.transpose(corners_3d)
# 3、将相机坐标系下的3D边界框的角点，投影到图像平面上，得到它们在图像上的2D坐标。
corners_2d = project_to_image(np.transpose(corners_3d), P);
return corners_2d, np.transpose(corners_3d)
def draw_projected_box3d(image, qs, color=(0,60,255), thickness=2):
'''
qs: 包含8个3D边界框角点坐标的数组, 形状为(8, 2)。图像坐标下的3D框, 8个顶点坐标。
'''
''' Draw 3d bounding box in image
qs: (8,2) array of vertices for the 3d box in following order:
1 -------- 0
/| /|
2 -------- 3 .
| | | |
. 5 -------- 4
|/ |/
6 -------- 7
'''
qs = qs.astype(np.int32) # 将输入的顶点坐标转换为整数类型，以便在图像上绘制。
# 这个循环迭代4次，每次处理一个边界框的一条边。
for k in range(0,4):
# Ref: http://docs.enthought.com/mayavi/mayavi/auto/mlab_helper_functions.html
# 定义了要绘制的边的起始点和结束点的索引。在这个循环中，它用于绘制边界框的前四条边。
i,j=k,(k+1)%4
cv2.line(image, (qs[i,0],qs[i,1]), (qs[j,0],qs[j,1]), color, thickness)
# 定义了要绘制的边的起始点和结束点的索引。在这个循环中，它用于绘制边界框的后四条边，与前四条边平行
i,j=k+4,(k+1)%4 + 4
cv2.line(image, (qs[i,0],qs[i,1]), (qs[j,0],qs[j,1]), color, thickness)
# 定义了要绘制的边的起始点和结束点的索引。在这个循环中，它用于绘制连接前四条边和后四条边的边界框的边。
i,j=k,k+4
cv2.line(image, (qs[i,0],qs[i,1]), (qs[j,0],qs[j,1]), color, thickness)
return image
9、点云3D结果-->图像BEV鸟瞰图结果（坐标系转换）
思路流程：
- 读取点云数据，点云得存储格式是n*4，n是指当前文件点云的数量，4分别表示（x，y，z，intensity），即点云的空间三维坐标、反射强度
- 我们只需读取前两行即可，得到坐标点（x，y）
- 然后将坐标点（x，y），画散点图
BEV鸟瞰图效果如下：
10、绘制BEV鸟瞰图
BEV图像示例效果：
核心代码：
'''
可视化BEV鸟瞰图
'''
def show_lidar_topview(pc_velo, objects, calib):
# 1-设置鸟瞰图范围
side_range = (-30, 30) # 左右距离
fwd_range = (0, 80) # 后前距离
x_points = pc_velo[:, 0]
y_points = pc_velo[:, 1]
z_points = pc_velo[:, 2]
# 2-获得区域内的点
f_filt = np.logical_and(x_points > fwd_range[0], x_points < fwd_range[1])
s_filt = np.logical_and(y_points > side_range[0], y_points < side_range[1])
filter = np.logical_and(f_filt, s_filt)
indices = np.argwhere(filter).flatten()
x_points = x_points[indices]
y_points = y_points[indices]
z_points = z_points[indices]
# 定义了鸟瞰图中每个像素代表的距离
res = 0.1
# 3-1将点云坐标系 转到 BEV坐标系
x_img = (-y_points / res).astype(np.int32)
y_img = (-x_points / res).astype(np.int32)
# 3-2调整坐标原点
x_img -= int(np.floor(side_range[0]) / res)
y_img += int(np.floor(fwd_range[1]) / res)
print(x_img.min(), x_img.max(), y_img.min(), y_img.max())
# 4-填充像素值, 将点云数据的高度信息（Z坐标）映射到像素值
height_range = (-3, 1.0)
pixel_value = np.clip(a=z_points, a_max=height_range[1], a_min=height_range[0])
def scale_to_255(a, min, max, dtype=np.uint8):
return ((a - min) / float(max - min) * 255).astype(dtype)
pixel_value = scale_to_255(pixel_value, height_range[0], height_range[1])
# 创建图像数组
x_max = 1 + int((side_range[1] - side_range[0]) / res)
y_max = 1 + int((fwd_range[1] - fwd_range[0]) / res)
im = np.zeros([y_max, x_max], dtype=np.uint8)
im[y_img, x_img] = pixel_value
im2 = Image.fromarray(im)
im2.save('save_output/BEV.png')
im2.show()
11、BEV鸟瞰图画2d框
在BEV视图中画框，可视化结果：
接口代码：
'''
将点云数据3D框投影到BEV
'''
def show_lidar_topview_with_boxes(img, objects, calib):
def bbox3d(obj):
box3d_pts_2d, box3d_pts_3d = utils.compute_box_3d(obj, calib.P) # 获取3D框-图像、3D框-相机坐标系
box3d_pts_3d_velo = calib.project_rect_to_velo(box3d_pts_3d) # 将相机坐标系的框 转到 激光雷达坐标系
return box3d_pts_3d_velo # 返回nx3的点
boxes3d = [bbox3d(obj) for obj in objects if obj.type == "Car"]
gt = np.array(boxes3d)
im2 = utils.draw_box3d_label_on_bev(img, gt, scores=None, thickness=1) # 获取激光雷达坐标系的3D点，选择x, y两维，画到BEV平面坐标系上
im2 = Image.fromarray(im2)
im2.save('save_output/BEV with boxes.png')
im2.show()
核心代码：
# 设置BEV鸟瞰图参数
side_range = (-30, 30) # 左右距离
fwd_range = (0, 80) # 后前距离
res = 0.1 # 分辨率0.05m
def compute_box_3d(obj, P):
'''
计算对象的3D边界框在图像平面上的投影
输入: obj代表一个物体标签信息, P代表相机的投影矩阵-内参。
输出: 返回两个值, corners_3d表示3D边界框在 相机坐标系 的8个角点的坐标-3D坐标。
corners_2d表示3D边界框在 图像上 的8个角点的坐标-2D坐标。
'''
# 计算一个绕Y轴旋转的旋转矩阵R，用于将3D坐标从世界坐标系转换到相机坐标系。obj.ry是对象的偏航角
R = roty(obj.ry)
# 物体实际的长、宽、高
l = obj.l;
w = obj.w;
h = obj.h;
# 存储了3D边界框的8个角点相对于对象中心的坐标。这些坐标定义了3D边界框的形状。
x_corners = [l/2,l/2,-l/2,-l/2,l/2,l/2,-l/2,-l/2];
y_corners = [0,0,0,0,-h,-h,-h,-h];
z_corners = [w/2,-w/2,-w/2,w/2,w/2,-w/2,-w/2,w/2];
# 1、将3D边界框的角点坐标从对象坐标系转换到相机坐标系。它使用了旋转矩阵R
corners_3d = np.dot(R, np.vstack([x_corners,y_corners,z_corners]))
# 3D边界框的坐标进行平移
corners_3d[0,:] = corners_3d[0,:] + obj.t[0];
corners_3d[1,:] = corners_3d[1,:] + obj.t[1];
corners_3d[2,:] = corners_3d[2,:] + obj.t[2];
# 2、检查对象是否在相机前方，因为只有在相机前方的对象才会被绘制。
# 如果对象的Z坐标（深度）小于0.1，就意味着对象在相机后方，那么corners_2d将被设置为None，函数将返回None。
if np.any(corners_3d[2,:]<0.1):
corners_2d = None
return corners_2d, np.transpose(corners_3d)
# 3、将相机坐标系下的3D边界框的角点，投影到图像平面上，得到它们在图像上的2D坐标。
corners_2d = project_to_image(np.transpose(corners_3d), P);
return corners_2d, np.transpose(corners_3d)
12、完整工程代码
工程目录：
kitti_vis_main.py（主代码入口）
from __future__ import print_function
import os
import sys
import cv2
import os.path
from PIL import Image
BASE_DIR = os.path.dirname(os.path.abspath(__file__))
ROOT_DIR = os.path.dirname(BASE_DIR)
sys.path.append(BASE_DIR)
sys.path.append(os.path.join(ROOT_DIR, 'mayavi'))
from kitti_object import *
def visualization():
import mayavi.mlab as mlab
dataset = kitti_object(os.path.join(ROOT_DIR, 'Kitti_3D_Vis/dataset/object')) # linux 路径
data_idx = 10 # 选择第几张图像
# 1-加载标签数据
objects = dataset.get_label_objects(data_idx)
print("There are %d objects.", len(objects))
# 2-加载图像
img = dataset.get_image(data_idx)
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
img_height, img_width, img_channel = img.shape
# 3-加载点云数据
pc_velo = dataset.get_lidar(data_idx)[:,0:3] # (x, y, z)
# 4-加载标定参数
calib = dataset.get_calibration(data_idx)
# 5-可视化原始图像
print(' ------------ show raw image -------- ')
Image.fromarray(img).show()
# 6-在图像中画2D框
print(' ------------ show image with 2D bounding box -------- ')
show_image_with_boxes(img, objects, calib, False)
# 7-在图像中画3D框
print(' ------------ show image with 3D bounding box ------- ')
show_image_with_boxes(img, objects, calib, True)
# 8-将点云数据投影到图像
print(' ----------- LiDAR points projected to image plane -- ')
show_lidar_on_image(pc_velo, img, calib, img_width, img_height)
# 9-画BEV图
print('------------------ BEV of LiDAR points -----------------------------')
show_lidar_topview(pc_velo, objects, calib)
# 10-在BEV图中画2D框
print('--------------- BEV of LiDAR points with bobes ---------------------')
img1 = cv2.imread('save_output/BEV.png')
img = cv2.cvtColor(img1, cv2.COLOR_BGR2RGB)
show_lidar_topview_with_boxes(img1, objects, calib)
if __name__=='__main__':
visualization()
kitti_util.py
from __future__ import print_function
import numpy as np
import cv2
from PIL import Image
import os
# 设置BEV鸟瞰图参数
side_range = (-30, 30) # 左右距离
fwd_range = (0, 80) # 后前距离
res = 0.1 # 分辨率0.05m
def compute_box_3d(obj, P):
'''
计算对象的3D边界框在图像平面上的投影
输入: obj代表一个物体标签信息, P代表相机的投影矩阵-内参。
输出: 返回两个值, corners_3d表示3D边界框在 相机坐标系 的8个角点的坐标-3D坐标。
corners_2d表示3D边界框在 图像上 的8个角点的坐标-2D坐标。
'''
# 计算一个绕Y轴旋转的旋转矩阵R，用于将3D坐标从世界坐标系转换到相机坐标系。obj.ry是对象的偏航角
R = roty(obj.ry)
# 物体实际的长、宽、高
l = obj.l;
w = obj.w;
h = obj.h;
# 存储了3D边界框的8个角点相对于对象中心的坐标。这些坐标定义了3D边界框的形状。
x_corners = [l/2,l/2,-l/2,-l/2,l/2,l/2,-l/2,-l/2];
y_corners = [0,0,0,0,-h,-h,-h,-h];
z_corners = [w/2,-w/2,-w/2,w/2,w/2,-w/2,-w/2,w/2];
# 1、将3D边界框的角点坐标从对象坐标系转换到相机坐标系。它使用了旋转矩阵R
corners_3d = np.dot(R, np.vstack([x_corners,y_corners,z_corners]))
# 3D边界框的坐标进行平移
corners_3d[0,:] = corners_3d[0,:] + obj.t[0];
corners_3d[1,:] = corners_3d[1,:] + obj.t[1];
corners_3d[2,:] = corners_3d[2,:] + obj.t[2];
# 2、检查对象是否在相机前方，因为只有在相机前方的对象才会被绘制。
# 如果对象的Z坐标（深度）小于0.1，就意味着对象在相机后方，那么corners_2d将被设置为None，函数将返回None。
if np.any(corners_3d[2,:]<0.1):
corners_2d = None
return corners_2d, np.transpose(corners_3d)
# 3、将相机坐标系下的3D边界框的角点，投影到图像平面上，得到它们在图像上的2D坐标。
corners_2d = project_to_image(np.transpose(corners_3d), P);
return corners_2d, np.transpose(corners_3d)
def project_to_image(pts_3d, P):
'''
将相机坐标系下的3D边界框的角点, 投影到图像平面上, 得到它们在图像上的2D坐标
输入: pts_3d是一个nx3的矩阵, 包含了待投影的3D坐标点(每行一个点), P是相机的投影矩阵, 通常是一个3x4的矩阵。
输出: 返回一个nx2的矩阵, 包含了投影到图像平面上的2D坐标点。
P(3x4) dot pts_3d_extended(4xn) = projected_pts_2d(3xn) => normalize projected_pts_2d(2xn)
<=> pts_3d_extended(nx4) dot P'(4x3) = projected_pts_2d(nx3) => normalize projected_pts_2d(nx2)
'''
n = pts_3d.shape[0] # 获取3D点的数量
pts_3d_extend = np.hstack((pts_3d, np.ones((n,1)))) # 将每个3D点的坐标扩展为齐次坐标形式（4D），通过在每个点的末尾添加1，创建了一个nx4的矩阵。
pts_2d = np.dot(pts_3d_extend, np.transpose(P)) # 将扩展的3D坐标点矩阵与投影矩阵P相乘，得到一个nx3的矩阵，其中每一行包含了3D点在图像平面上的投影坐标。每个点的坐标表示为[x, y, z]。
pts_2d[:,0] /= pts_2d[:,2] # 将投影坐标中的x坐标除以z坐标，从而获得2D图像上的x坐标。
pts_2d[:,1] /= pts_2d[:,2] # 将投影坐标中的y坐标除以z坐标，从而获得2D图像上的y坐标。
return pts_2d[:,0:2] # 返回一个nx2的矩阵,其中包含了每个3D点在2D图像上的坐标。
def draw_projected_box3d(image, qs, color=(0,60,255), thickness=2):
'''
qs: 包含8个3D边界框角点坐标的数组, 形状为(8, 2)。图像坐标下的3D框, 8个顶点坐标。
'''
''' Draw 3d bounding box in image
qs: (8,2) array of vertices for the 3d box in following order:
1 -------- 0
/| /|
2 -------- 3 .
| | | |
. 5 -------- 4
|/ |/
6 -------- 7
'''
qs = qs.astype(np.int32) # 将输入的顶点坐标转换为整数类型，以便在图像上绘制。
# 这个循环迭代4次，每次处理一个边界框的一条边。
for k in range(0,4):
# Ref: http://docs.enthought.com/mayavi/mayavi/auto/mlab_helper_functions.html
# 定义了要绘制的边的起始点和结束点的索引。在这个循环中，它用于绘制边界框的前四条边。
i,j=k,(k+1)%4
cv2.line(image, (qs[i,0],qs[i,1]), (qs[j,0],qs[j,1]), color, thickness)
# 定义了要绘制的边的起始点和结束点的索引。在这个循环中，它用于绘制边界框的后四条边，与前四条边平行
i,j=k+4,(k+1)%4 + 4
cv2.line(image, (qs[i,0],qs[i,1]), (qs[j,0],qs[j,1]), color, thickness)
# 定义了要绘制的边的起始点和结束点的索引。在这个循环中，它用于绘制连接前四条边和后四条边的边界框的边。
i,j=k,k+4
cv2.line(image, (qs[i,0],qs[i,1]), (qs[j,0],qs[j,1]), color, thickness)
return image
def draw_box3d_label_on_bev(image, boxes3d, thickness=1, scores=None):
# if scores is not None and scores.shape[0] >0:
img = image.copy()
num = len(boxes3d)
for n in range(num):
b = boxes3d[n]
x0 = b[0, 0]
y0 = b[0, 1]
x1 = b[1, 0]
y1 = b[1, 1]
x2 = b[2, 0]
y2 = b[2, 1]
x3 = b[3, 0]
y3 = b[3, 1]
if (x0<30 and x1<30 and x2<30 and x3<30):
u0, v0 = lidar_to_top_coords(x0, y0)
u1, v1 = lidar_to_top_coords(x1, y1)
u2, v2 = lidar_to_top_coords(x2, y2)
u3, v3 = lidar_to_top_coords(x3, y3)
color = (0, 255, 0) # green
cv2.line(img, (u0, v0), (u1, v1), color, thickness, cv2.LINE_AA)
cv2.line(img, (u1, v1), (u2, v2), color, thickness, cv2.LINE_AA)
cv2.line(img, (u2, v2), (u3, v3), color, thickness, cv2.LINE_AA)
cv2.line(img, (u3, v3), (u0, v0), color, thickness, cv2.LINE_AA)
elif (x0<50 and x1<50 and x2<50 and x3<50):
color = (255, 0, 0) # red
u0, v0 = lidar_to_top_coords(x0, y0)
u1, v1 = lidar_to_top_coords(x1, y1)
u2, v2 = lidar_to_top_coords(x2, y2)
u3, v3 = lidar_to_top_coords(x3, y3)
cv2.line(img, (u0, v0), (u1, v1), color, thickness, cv2.LINE_AA)
cv2.line(img, (u1, v1), (u2, v2), color, thickness, cv2.LINE_AA)
cv2.line(img, (u2, v2), (u3, v3), color, thickness, cv2.LINE_AA)
cv2.line(img, (u3, v3), (u0, v0), color, thickness, cv2.LINE_AA)
else:
color = (0, 0, 255) # blue
u0, v0 = lidar_to_top_coords(x0, y0)
u1, v1 = lidar_to_top_coords(x1, y1)
u2, v2 = lidar_to_top_coords(x2, y2)
u3, v3 = lidar_to_top_coords(x3, y3)
cv2.line(img, (u0, v0), (u1, v1), color, thickness, cv2.LINE_AA)
cv2.line(img, (u1, v1), (u2, v2), color, thickness, cv2.LINE_AA)
cv2.line(img, (u2, v2), (u3, v3), color, thickness, cv2.LINE_AA)
cv2.line(img, (u3, v3), (u0, v0), color, thickness, cv2.LINE_AA)
return img
def draw_box3d_predict_on_bev(image, boxes3d, thickness=1, scores=None):
# if scores is not None and scores.shape[0] >0:
img = image.copy()
num = len(boxes3d)
for n in range(num):
b = boxes3d[n]
x0 = b[0, 0]
y0 = b[0, 1]
x1 = b[1, 0]
y1 = b[1, 1]
x2 = b[2, 0]
y2 = b[2, 1]
x3 = b[3, 0]
y3 = b[3, 1]
color = (255, 255, 255) # white
u0, v0 = lidar_to_top_coords(x0, y0)
u1, v1 = lidar_to_top_coords(x1, y1)
u2, v2 = lidar_to_top_coords(x2, y2)
u3, v3 = lidar_to_top_coords(x3, y3)
cv2.line(img, (u0, v0), (u1, v1), color, thickness, cv2.LINE_AA)
cv2.line(img, (u1, v1), (u2, v2), color, thickness, cv2.LINE_AA)
cv2.line(img, (u2, v2), (u3, v3), color, thickness, cv2.LINE_AA)
cv2.line(img, (u3, v3), (u0, v0), color, thickness, cv2.LINE_AA)
return img
def lidar_to_top_coords(x, y, z=None):
if 0:
return x, y
else:
# print("TOP_X_MAX-TOP_X_MIN:",TOP_X_MAX,TOP_X_MIN)
xx = (-y / res).astype(np.int32)
yy = (-x / res).astype(np.int32)
# 调整坐标原点
xx -= int(np.floor(side_range[0]) / res)
yy += int(np.floor(fwd_range[1]) / res)
return xx, yy
# 解析标签数据
class Object3d(object):
''' 3d object label '''
def __init__(self, label_file_line):
data = label_file_line.split(' ')
data[1:] = [float(x) for x in data[1:]]
# extract label, truncation, occlusion
self.type = data[0] # 'Car', 'Pedestrian', ...
self.truncation = data[1] # truncated pixel ratio [0..1]
self.occlusion = int(data[2]) # 0=visible, 1=partly occluded, 2=fully occluded, 3=unknown
self.alpha = data[3] # object observation angle [-pi..pi]
# extract 2d bounding box in 0-based coordinates
self.xmin = data[4] # left
self.ymin = data[5] # top
self.xmax = data[6] # right
self.ymax = data[7] # bottom
self.box2d = np.array([self.xmin,self.ymin,self.xmax,self.ymax])
# extract 3d bounding box information
self.h = data[8] # box height
self.w = data[9] # box width
self.l = data[10] # box length (in meters)
self.t = (data[11],data[12],data[13]) # location (x,y,z) in camera coord.
self.ry = data[14] # yaw angle (around Y-axis in camera coordinates) [-pi..pi]
def print_object(self):
print('Type, truncation, occlusion, alpha: %s, %d, %d, %f' % \
(self.type, self.truncation, self.occlusion, self.alpha))
print('2d bbox (x0,y0,x1,y1): %f, %f, %f, %f' % \
(self.xmin, self.ymin, self.xmax, self.ymax))
print('3d bbox h,w,l: %f, %f, %f' % \
(self.h, self.w, self.l))
print('3d bbox location, ry: (%f, %f, %f), %f' % \
(self.t[0],self.t[1],self.t[2],self.ry))
class Calibration(object):
''' Calibration matrices and utils
3d XYZ in <label>.txt are in rect camera coord.
2d box xy are in image2 coord
Points in <lidar>.bin are in Velodyne coord.
y_image2 = P^2_rect * x_rect
y_image2 = P^2_rect * R0_rect * Tr_velo_to_cam * x_velo
x_ref = Tr_velo_to_cam * x_velo
x_rect = R0_rect * x_ref
P^2_rect = [f^2_u, 0, c^2_u, -f^2_u b^2_x;
0, f^2_v, c^2_v, -f^2_v b^2_y;
0, 0, 1, 0]
= K * [1|t]
image2 coord:
----> x-axis (u)
|
|
v y-axis (v)
velodyne coord:
front x, left y, up z
rect/ref camera coord:
right x, down y, front z
Ref (KITTI paper): http://www.cvlibs.net/publications/Geiger2013IJRR.pdf
TODO(rqi): do matrix multiplication only once for each projection.
'''
def __init__(self, calib_filepath, from_video=False):
if from_video:
calibs = self.read_calib_from_video(calib_filepath)
else:
calibs = self.read_calib_file(calib_filepath)
# Projection matrix from rect camera coord to image2 coord
self.P = calibs['P2']
self.P = np.reshape(self.P, [3,4])
# Rigid transform from Velodyne coord to reference camera coord
self.V2C = calibs['Tr_velo_to_cam']
self.V2C = np.reshape(self.V2C, [3,4])
self.C2V = inverse_rigid_trans(self.V2C)
# Rotation from reference camera coord to rect camera coord
self.R0 = calibs['R0_rect']
self.R0 = np.reshape(self.R0,[3,3])
# Camera intrinsics and extrinsics
self.c_u = self.P[0,2]
self.c_v = self.P[1,2]
self.f_u = self.P[0,0]
self.f_v = self.P[1,1]
self.b_x = self.P[0,3]/(-self.f_u) # relative
self.b_y = self.P[1,3]/(-self.f_v)
def read_calib_file(self, filepath):
''' Read in a calibration file and parse into a dictionary.'''
data = {}
with open(filepath, 'r') as f:
for line in f.readlines():
line = line.rstrip()
if len(line)==0: continue
key, value = line.split(':', 1)
# The only non-float values in these files are dates, which
# we don't care about anyway
try:
data[key] = np.array([float(x) for x in value.split()])
except ValueError:
pass
return data
def read_calib_from_video(self, calib_root_dir):
''' Read calibration for camera 2 from video calib files.
there are calib_cam_to_cam and calib_velo_to_cam under the calib_root_dir
'''
data = {}
cam2cam = self.read_calib_file(os.path.join(calib_root_dir, 'calib_cam_to_cam.txt'))
velo2cam = self.read_calib_file(os.path.join(calib_root_dir, 'calib_velo_to_cam.txt'))
Tr_velo_to_cam = np.zeros((3,4))
Tr_velo_to_cam[0:3,0:3] = np.reshape(velo2cam['R'], [3,3])
Tr_velo_to_cam[:,3] = velo2cam['T']
data['Tr_velo_to_cam'] = np.reshape(Tr_velo_to_cam, [12])
data['R0_rect'] = cam2cam['R_rect_00']
data['P2'] = cam2cam['P_rect_02']
return data
def cart2hom(self, pts_3d):
''' Input: nx3 points in Cartesian
Oupput: nx4 points in Homogeneous by pending 1
'''
n = pts_3d.shape[0]
pts_3d_hom = np.hstack((pts_3d, np.ones((n,1))))
return pts_3d_hom
# ===========================
# ------- 3d to 3d ----------
# ===========================
def project_velo_to_ref(self, pts_3d_velo):
pts_3d_velo = self.cart2hom(pts_3d_velo) # nx4
return np.dot(pts_3d_velo, np.transpose(self.V2C))
def project_ref_to_velo(self, pts_3d_ref):
pts_3d_ref = self.cart2hom(pts_3d_ref) # nx4
return np.dot(pts_3d_ref, np.transpose(self.C2V))
def project_rect_to_ref(self, pts_3d_rect):
''' Input and Output are nx3 points '''
return np.transpose(np.dot(np.linalg.inv(self.R0), np.transpose(pts_3d_rect)))
def project_ref_to_rect(self, pts_3d_ref):
''' Input and Output are nx3 points '''
return np.transpose(np.dot(self.R0, np.transpose(pts_3d_ref)))
def project_rect_to_velo(self, pts_3d_rect):
''' Input: nx3 points in rect camera coord.
Output: nx3 points in velodyne coord.
'''
pts_3d_ref = self.project_rect_to_ref(pts_3d_rect)
return self.project_ref_to_velo(pts_3d_ref)
def project_velo_to_rect(self, pts_3d_velo):
pts_3d_ref = self.project_velo_to_ref(pts_3d_velo)
return self.project_ref_to_rect(pts_3d_ref)
def corners3d_to_img_boxes(self, corners3d):
"""
:param corners3d: (N, 8, 3) corners in rect coordinate
:return: boxes: (None, 4) [x1, y1, x2, y2] in rgb coordinate
:return: boxes_corner: (None, 8) [xi, yi] in rgb coordinate
"""
sample_num = corners3d.shape[0]
corners3d_hom = np.concatenate((corners3d, np.ones((sample_num, 8, 1))), axis=2) # (N, 8, 4)
img_pts = np.matmul(corners3d_hom, self.P.T) # (N, 8, 3)
x, y = img_pts[:, :, 0] / img_pts[:, :, 2], img_pts[:, :, 1] / img_pts[:, :, 2]
x1, y1 = np.min(x, axis=1), np.min(y, axis=1)
x2, y2 = np.max(x, axis=1), np.max(y, axis=1)
boxes = np.concatenate((x1.reshape(-1, 1), y1.reshape(-1, 1), x2.reshape(-1, 1), y2.reshape(-1, 1)), axis=1)
boxes_corner = np.concatenate((x.reshape(-1, 8, 1), y.reshape(-1, 8, 1)), axis=2)
return boxes, boxes_corner
# ===========================
# ------- 3d to 2d ----------
# ===========================
def project_rect_to_image(self, pts_3d_rect):
''' Input: nx3 points in rect camera coord.
Output: nx2 points in image2 coord.
'''
pts_3d_rect = self.cart2hom(pts_3d_rect)
pts_2d = np.dot(pts_3d_rect, np.transpose(self.P)) # nx3
pts_2d[:,0] /= pts_2d[:,2]
pts_2d[:,1] /= pts_2d[:,2]
return pts_2d[:,0:2]
def project_velo_to_image(self, pts_3d_velo):
''' Input: nx3 points in velodyne coord.
Output: nx2 points in image2 coord.
'''
pts_3d_rect = self.project_velo_to_rect(pts_3d_velo)
return self.project_rect_to_image(pts_3d_rect)
# ===========================
# ------- 2d to 3d ----------
# ===========================
def project_image_to_rect(self, uv_depth):
''' Input: nx3 first two channels are uv, 3rd channel
is depth in rect camera coord.
Output: nx3 points in rect camera coord.
'''
n = uv_depth.shape[0]
x = ((uv_depth[:,0]-self.c_u)*uv_depth[:,2])/self.f_u + self.b_x
y = ((uv_depth[:,1]-self.c_v)*uv_depth[:,2])/self.f_v + self.b_y
pts_3d_rect = np.zeros((n,3))
pts_3d_rect[:,0] = x
pts_3d_rect[:,1] = y
pts_3d_rect[:,2] = uv_depth[:,2]
return pts_3d_rect
def project_image_to_velo(self, uv_depth):
pts_3d_rect = self.project_image_to_rect(uv_depth)
return self.project_rect_to_velo(pts_3d_rect)
def rotx(t):
''' 3D Rotation about the x-axis. '''
c = np.cos(t)
s = np.sin(t)
return np.array([[1, 0, 0],
[0, c, -s],
[0, s, c]])
def roty(t):
''' Rotation about the y-axis. '''
c = np.cos(t)
s = np.sin(t)
return np.array([[c, 0, s],
[0, 1, 0],
[-s, 0, c]])
def rotz(t):
''' Rotation about the z-axis. '''
c = np.cos(t)
s = np.sin(t)
return np.array([[c, -s, 0],
[s, c, 0],
[0, 0, 1]])
def transform_from_rot_trans(R, t):
''' Transforation matrix from rotation matrix and translation vector. '''
R = R.reshape(3, 3)
t = t.reshape(3, 1)
return np.vstack((np.hstack([R, t]), [0, 0, 0, 1]))
def inverse_rigid_trans(Tr):
''' Inverse a rigid body transform matrix (3x4 as [R|t])
[R'|-R't; 0|1]
'''
inv_Tr = np.zeros_like(Tr) # 3x4
inv_Tr[0:3,0:3] = np.transpose(Tr[0:3,0:3])
inv_Tr[0:3,3] = np.dot(-np.transpose(Tr[0:3,0:3]), Tr[0:3,3])
return inv_Tr
def read_label(label_filename):
lines = [line.rstrip() for line in open(label_filename)]
objects = [Object3d(line) for line in lines]
return objects
def load_image(img_filename):
return cv2.imread(img_filename)
def load_velo_scan(velo_filename):
scan = np.fromfile(velo_filename, dtype=np.float32)
scan = scan.reshape((-1, 4))
return scan
kitti_object.py
from __future__ import print_function
import os
import sys
import cv2
import numpy as np
from PIL import Image
import matplotlib.pyplot as plt
BASE_DIR = os.path.dirname(os.path.abspath(__file__))
ROOT_DIR = os.path.dirname(BASE_DIR)
sys.path.append(os.path.join(ROOT_DIR, 'mayavi'))
import kitti_util as utils
'''
在图像中画2D框、3D框
'''
def show_image_with_boxes(img, objects, calib, show3d=True):
img1 = np.copy(img) # for 2d bbox
img2 = np.copy(img) # for 3d bbox
for obj in objects:
if obj.type=='DontCare':continue
cv2.rectangle(img1, (int(obj.xmin),int(obj.ymin)), (int(obj.xmax),int(obj.ymax)), (0,255,0), 2) # 画2D框
box3d_pts_2d, box3d_pts_3d = utils.compute_box_3d(obj, calib.P) # 获取图像3D框(8*2)、相机坐标系3D框(8*3)
img2 = utils.draw_projected_box3d(img2, box3d_pts_2d) # 在图像上画3D框
if show3d:
Image.fromarray(img2).save('save_output/image_with_3Dboxes.png')
Image.fromarray(img2).show()
else:
Image.fromarray(img1).save('save_output/image_with_2Dboxes.png')
Image.fromarray(img1).show()
'''
可视化BEV鸟瞰图
'''
def show_lidar_topview(pc_velo, objects, calib):
# 1-设置鸟瞰图范围
side_range = (-30, 30) # 左右距离
fwd_range = (0, 80) # 后前距离
x_points = pc_velo[:, 0]
y_points = pc_velo[:, 1]
z_points = pc_velo[:, 2]
# 2-获得区域内的点
f_filt = np.logical_and(x_points > fwd_range[0], x_points < fwd_range[1])
s_filt = np.logical_and(y_points > side_range[0], y_points < side_range[1])
filter = np.logical_and(f_filt, s_filt)
indices = np.argwhere(filter).flatten()
x_points = x_points[indices]
y_points = y_points[indices]
z_points = z_points[indices]
# 定义了鸟瞰图中每个像素代表的距离
res = 0.1
# 3-1将点云坐标系 转到 BEV坐标系
x_img = (-y_points / res).astype(np.int32)
y_img = (-x_points / res).astype(np.int32)
# 3-2调整坐标原点
x_img -= int(np.floor(side_range[0]) / res)
y_img += int(np.floor(fwd_range[1]) / res)
print(x_img.min(), x_img.max(), y_img.min(), y_img.max())
# 4-填充像素值, 将点云数据的高度信息（Z坐标）映射到像素值
height_range = (-3, 1.0)
pixel_value = np.clip(a=z_points, a_max=height_range[1], a_min=height_range[0])
def scale_to_255(a, min, max, dtype=np.uint8):
return ((a - min) / float(max - min) * 255).astype(dtype)
pixel_value = scale_to_255(pixel_value, height_range[0], height_range[1])
# 创建图像数组
x_max = 1 + int((side_range[1] - side_range[0]) / res)
y_max = 1 + int((fwd_range[1] - fwd_range[0]) / res)
im = np.zeros([y_max, x_max], dtype=np.uint8)
im[y_img, x_img] = pixel_value
im2 = Image.fromarray(im)
im2.save('save_output/BEV.png')
im2.show()
'''
将点云数据3D框投影到BEV
'''
def show_lidar_topview_with_boxes(img, objects, calib):
def bbox3d(obj):
box3d_pts_2d, box3d_pts_3d = utils.compute_box_3d(obj, calib.P) # 获取3D框-图像、3D框-相机坐标系
box3d_pts_3d_velo = calib.project_rect_to_velo(box3d_pts_3d) # 将相机坐标系的框 转到 激光雷达坐标系
return box3d_pts_3d_velo # 返回nx3的点
boxes3d = [bbox3d(obj) for obj in objects if obj.type == "Car"]
gt = np.array(boxes3d)
im2 = utils.draw_box3d_label_on_bev(img, gt, scores=None, thickness=1) # 获取激光雷达坐标系的3D点，选择x, y两维，画到BEV平面坐标系上
im2 = Image.fromarray(im2)
im2.save('save_output/BEV with boxes.png')
im2.show()
'''
将点云数据投影到图像
'''
def show_lidar_on_image(pc_velo, img, calib, img_width, img_height):
''' Project LiDAR points to image '''
imgfov_pc_velo, pts_2d, fov_inds = get_lidar_in_image_fov(pc_velo,
calib, 0, 0, img_width, img_height, True)
imgfov_pts_2d = pts_2d[fov_inds,:]
imgfov_pc_rect = calib.project_velo_to_rect(imgfov_pc_velo)
import matplotlib.pyplot as plt
cmap = plt.cm.get_cmap('hsv', 256)
cmap = np.array([cmap(i) for i in range(256)])[:,:3]*255
for i in range(imgfov_pts_2d.shape[0]):
depth = imgfov_pc_rect[i,2]
color = cmap[int(640.0/depth),:]
cv2.circle(img, (int(np.round(imgfov_pts_2d[i,0])),
int(np.round(imgfov_pts_2d[i,1]))),
2, color=tuple(color), thickness=-1)
Image.fromarray(img).save('save_output/lidar_on_image.png')
Image.fromarray(img).show()
return img
'''
将点云数据投影到相机坐标系
'''
def get_lidar_in_image_fov(pc_velo, calib, xmin, ymin, xmax, ymax,
return_more=False, clip_distance=2.0):
''' Filter lidar points, keep those in image FOV '''
pts_2d = calib.project_velo_to_image(pc_velo)
fov_inds = (pts_2d[:,0]<xmax) & (pts_2d[:,0]>=xmin) & \
(pts_2d[:,1]<ymax) & (pts_2d[:,1]>=ymin)
fov_inds = fov_inds & (pc_velo[:,0]>clip_distance)
imgfov_pc_velo = pc_velo[fov_inds,:]
if return_more:
return imgfov_pc_velo, pts_2d, fov_inds
else:
return imgfov_pc_velo
'''
解析标签
'''
class kitti_object(object):
'''Load and parse object data into a usable format.'''
def __init__(self, root_dir, split='training'):
'''root_dir contains training and testing folders'''
self.root_dir = root_dir
self.split = split
self.split_dir = os.path.join(root_dir, split)
if split == 'training':
self.num_samples = 7481
elif split == 'testing':
self.num_samples = 7518
else:
print('Unknown split: %s' % (split))
exit(-1)
self.image_dir = os.path.join(self.split_dir, 'image_2')
self.calib_dir = os.path.join(self.split_dir, 'calib')
self.lidar_dir = os.path.join(self.split_dir, 'velodyne')
self.label_dir = os.path.join(self.split_dir, 'label_2')
def __len__(self):
return self.num_samples
def get_image(self, idx):
assert(idx<self.num_samples)
img_filename = os.path.join(self.image_dir, '%06d.png'%(idx))
return utils.load_image(img_filename)
def get_lidar(self, idx):
assert(idx<self.num_samples)
lidar_filename = os.path.join(self.lidar_dir, '%06d.bin'%(idx))
return utils.load_velo_scan(lidar_filename)
def get_calibration(self, idx):
assert(idx<self.num_samples)
calib_filename = os.path.join(self.calib_dir, '%06d.txt'%(idx))
return utils.Calibration(calib_filename)
def get_label_objects(self, idx):
assert(idx<self.num_samples and self.split=='training')
label_filename = os.path.join(self.label_dir, '%06d.txt'%(idx))
return utils.read_label(label_filename)
def get_depth_map(self, idx):
pass
def get_top_down(self, idx):
pass
运行程序后kitti_vis_main.py后，回保存5张结果图片
后面还会介绍Nuscenes、Waymo等3D数据集。
本文转载自: https://blog.csdn.net/qq_41204464/article/details/132776800
版权归原作者 一颗小树x 所有， 如有侵权，请联系我们删除。
版权归原作者 一颗小树x 所有， 如有侵权，请联系我们删除。