rclcpp::Time when = this->get_clock()->now() - rclcpp::Duration(5, 0); t = tf_buffer_->lookupTransfo...
时间: 2024-05-31 15:13:55 浏览: 11
这段代码是使用ROS2中的rclcpp库实现的,主要是用于获取当前时间,并从tf2缓存中查询变换矩阵。
首先,rclcpp::Time when = this->get_clock()->now() - rclcpp::Duration(5, 0); 获取当前时间减去5秒,得到一个时间点。其中,rclcpp::Time是ROS2中的时间类型,它提供了一些时间相关的操作。
然后,t = tf_buffer_->lookupTransform(target_frame, source_frame, when); 通过tf2缓存查询变换矩阵。tf2是ROS2中的一个库,用于处理坐标系之间的转换。其中,target_frame和source_frame分别表示目标坐标系和源坐标系,when表示查询的时间点。lookupTransform函数会返回一个tf2::StampedTransform对象,它包含了查询到的变换矩阵以及时间戳等信息。
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c++ string "%02d:%02d:%02d:%06ld", timenow->tm_hour, timenow->tm_min, timenow->tm_sec, time.tv_usec
This is a C string that uses format specifiers to construct a message that includes the current time. The format specifiers are:
- `%d`: integer decimal format
- `%ld`: long integer decimal format
The message format is:
`"\x02d:\x02d:\x02d:\x06ld"`
- `\x02`: represents the ASCII control character STX (start of text), which is equivalent to character 2.
- `\x06`: represents the ASCII control character ACK (acknowledge), which is equivalent to character 6.
When the string is printed, the format specifiers will be replaced with the corresponding values provided as arguments. `timenow->tm_hour`, `timenow->tm_min`, and `timenow->tm_sec` are integers representing the current hour, minute, and second, respectively. `time.tv_usec` is a long integer representing the current microsecond.
For example, if the current time is 01:23:45.678910, the string would be printed as:
`"\x021:\x023:\x024:\x06678910"`
picture->pkt_dts = p->avpkt->dts;
This line of code sets the `pkt_dts` field of a `picture` struct to the `dts` field of the `avpkt` struct of another struct `p`.
`pkt_dts` represents the Decoding Time Stamp of a video frame, which is the timestamp indicating when the frame should be decoded and displayed. `avpkt` is an `AVPacket` struct in the FFmpeg library, which contains compressed data of a video or audio frame. `dts` stands for Decoding Time Stamp and is a field in the `AVPacket` struct that holds the decoding timestamp of the packet.
Therefore, this line of code is used to assign the decoding timestamp of a video frame to the `pkt_dts` field of a `picture` struct, which can be used in further processing of the video frames.