在数据结构中ASL是啥？

Posted 2023-04-25

是平均查找长度么？

参考技术A 是的，英语是 average search length

ASL数据转换为ROS bag数据

故跬步不休，跛鳖千里；累积不辍，可成丘阜。——（西汉）刘安《淮南子·说林训》

差不多从夏天的时候开始就一直在找有没有什么方法可以生成ROS bag数据，当时只找到了录制的方法，使用图片等原始数据生成的方法一直没找到。直到最近看到一篇博客使用了一个Python脚本将ASL数据转换成了ROS bag，试了一下挺好用的，欣喜若狂。有了它就可以将自己的数据按照ASL格式进行组织，之后使用脚本直接生成ROS bag就可以了。

简单说一下使用方法。因为需要用到ROS的一些Python包，所以使用的Python环境必须是安装了ROS的。我是在Ubuntu 16.04 LTS下运行的，安装的ROS Kinetic，运行环境其实和这篇博客的一样：一周小结（七）——从零开始配置VINS-Mono运行环境。不知道什么原因，在Pycharm中导入相关包时一直报错，但是相同的Python版本在终端却可以，大家如果有知道什么原因的欢迎评论区留言。所以无奈就抛弃了IDE而在终端运行，使用时需要给出ASL数据解压的文件路径以及生成的ROS bag数据的路径、名称，后者可以使用默认值（home文件夹下生成output.bag），例如：

python '/home/dong/Code/zip2bag/zip2bag.py'  --folder /home/dong/catkin_ws/dataset/1

最后给出Python脚本。大家也可以根据自己数据的组织结构、命名规则等进行适当修改。

#!/usr/bin/env python
print
"importing libraries"

import rosbag
import rospy
from sensor_msgs.msg import Image
from sensor_msgs.msg import Imu
from geometry_msgs.msg import PointStamped
# import ImageFile
# import PIL.ImageFile as ImageFile
import time, sys, os
import argparse
import cv2
import numpy as np
import csv

# structure
# dataset/cam0/data/TIMESTAMP.png
# dataset/camN/data/TIMESTAMP.png
# dataset/imu0/data.csv
# dataset/imuN/data.csv
# dataset/leica0/data.csv

# setup the argument list
parser = argparse.ArgumentParser(description='Create a ROS bag using the images and imu data.')
parser.add_argument('--folder', metavar='folder', nargs='?', help='Data folder')
parser.add_argument('--output_bag', metavar='output_bag', default="output.bag", help='ROS bag file %(default)s')

# print help if no argument is specified
if len(sys.argv) < 2:
    parser.print_help()
    sys.exit(0)

# parse the args
parsed = parser.parse_args()


def getImageFilesFromDir(dir):
    '''Generates a list of files from the directory'''
    image_files = list()
    timestamps = list()
    if os.path.exists(dir):
        for path, names, files in os.walk(dir):
            for f in files:
                if os.path.splitext(f)[1] in ['.bmp', '.png', '.jpg']:
                    image_files.append(os.path.join(path, f))
                    timestamps.append(os.path.splitext(f)[0])
                    # sort by timestamp
    sort_list = sorted(zip(timestamps, image_files))
    image_files = [file[1] for file in sort_list]
    return image_files


def getCamFoldersFromDir(dir):
    '''Generates a list of all folders that start with cam e.g. cam0'''
    cam_folders = list()
    if os.path.exists(dir):
        for path, folders, files in os.walk(dir):
            for folder in folders:
                if folder[0:3] == "cam":
                    cam_folders.append(folder)
    return cam_folders


def getImuFoldersFromDir(dir):
    '''Generates a list of all folders that start with imu e.g. cam0'''
    imu_folders = list()
    if os.path.exists(dir):
        for path, folders, files in os.walk(dir):
            for folder in folders:
                if folder[0:3] == "imu":
                    imu_folders.append(folder)
    return imu_folders


def getImuCsvFiles(dir):
    '''Generates a list of all csv files that start with imu'''
    imu_files = list()
    if os.path.exists(dir):
        for path, folders, files in os.walk(dir):
            for file in files:
                if file[0:3] == 'imu' and os.path.splitext(file)[1] == ".csv":
                    imu_files.append(os.path.join(path, file))

    return imu_files


def loadImageToRosMsg(filename):
    image_np = cv2.imread(filename, cv2.IMREAD_GRAYSCALE)

    timestamp_nsecs = os.path.splitext(os.path.basename(filename))[0]
    timestamp = rospy.Time(secs=int(timestamp_nsecs[0:-9]), nsecs=int(timestamp_nsecs[-9:]))

    rosimage = Image()
    rosimage.header.stamp = timestamp
    rosimage.height = image_np.shape[0]
    rosimage.width = image_np.shape[1]
    rosimage.step = rosimage.width  # only with mono8! (step = width * byteperpixel * numChannels)
    rosimage.encoding = "mono8"
    rosimage.data = image_np.tostring()

    return rosimage, timestamp


def createImuMessge(timestamp_int, omega, alpha):
    timestamp_nsecs = str(timestamp_int)
    timestamp = rospy.Time(int(timestamp_nsecs[0:-9]), int(timestamp_nsecs[-9:]))

    rosimu = Imu()
    rosimu.header.stamp = timestamp
    rosimu.angular_velocity.x = float(omega[0])
    rosimu.angular_velocity.y = float(omega[1])
    rosimu.angular_velocity.z = float(omega[2])
    rosimu.linear_acceleration.x = float(alpha[0])
    rosimu.linear_acceleration.y = float(alpha[1])
    rosimu.linear_acceleration.z = float(alpha[2])

    return rosimu, timestamp

# create the bag
bag = rosbag.Bag(parsed.output_bag, 'w')

# write images
camfolders = getCamFoldersFromDir(parsed.folder)
for camfolder in camfolders:
    camdir = parsed.folder + "/0".format(camfolder) + "/data"
    image_files = getImageFilesFromDir(camdir)
    for image_filename in image_files:
        image_msg, timestamp = loadImageToRosMsg(image_filename)
        bag.write("/0/image_raw".format(camfolder), image_msg, timestamp)

# write imu data
imufolders = getImuFoldersFromDir(parsed.folder)
for imufolder in imufolders:
    imufile = parsed.folder + "/" + imufolder + "/data.csv"
    topic = os.path.splitext(os.path.basename(imufolder))[0]
    with open(imufile, 'rb') as csvfile:
        reader = csv.reader(csvfile, delimiter=',')
        headers = next(reader, None)
        for row in reader:
            imumsg, timestamp = createImuMessge(row[0], row[1:4], row[4:7])
            bag.write("/0".format(topic), imumsg, timestamp)

# write leica data
leicafile = parsed.folder + "/leica0/data.csv"
with open(leicafile, 'rb') as csvfile:
    reader = csv.reader(csvfile, delimiter=',')
    headers = next(reader, None)
    for row in reader:
        timestamp_nsecs = str(row[0])
        timestamp = rospy.Time( int(timestamp_nsecs[0:-9]), int(timestamp_nsecs[-9:]) )

        pos = PointStamped()
        pos.header.stamp = timestamp
        pos.point.x = float(row[1])
        pos.point.y = float(row[2])
        pos.point.z = float(row[3])
        bag.write("/leica/position", pos, timestamp)

bag.close()

又到年底了，一年快要结束了。去年因为出差的原因（其实就是因为懒），没有写年终总结与新年展望。今年可不能这样了，先给自己立一个小小的flag，O(∩_∩)O哈哈~，年底见！

参考：

1、The EuRoC MAV Dataset

2、从 EuRoC MAV Dataset 的 .zip 文件生成 .bag 的 python 脚本