In this example, we will review the [image_view](http://wiki.ros.org/image_view?distro=melodic) ROS package and a Python script that captures an image from the RealSense camera.
In this example, we will review the [image_view](http://wiki.ros.org/image_view?distro=melodic) ROS package and a Python script that captures an image from the [RealSense camera](https://www.intelrealsense.com/depth-camera-d435i/).
Begin by checking out the [feature/upright_camera_view](https://github.com/hello-robot/stretch_ros/tree/feature/upright_camera_view) branch in the stretch_ros repository. The configuration of the camera results in the images being displayed sideways. Thus, this branch publishes a new topic that rotates the raw image upright.
Begin by checking out the [feature/upright_camera_view](https://github.com/hello-robot/stretch_ros/tree/feature/upright_camera_view) branch in the [stretch_ros](https://github.com/hello-robot/stretch_ros) repository. The configuration of the camera results in the images being displayed sideways. Thus, this branch publishes a new topic that rotates the raw image upright.
```bash
cd ~/catkin_ws/src/stretch_ros/stretch_core
@ -21,14 +19,12 @@ Then run the stretch driver launch file.
# Terminal 1
roslaunch stretch_core stretch_driver.launch
```
To activate the RealSense camera and publish topics to be visualized, run the following launch file in a new terminal.
To activate the [RealSense camera](https://www.intelrealsense.com/depth-camera-d435i/) and publish topics to be visualized, run the following launch file in a new terminal.
Within this tutorial package, there is an RViz config file with the topics for perception already in the Display tree. You can visualize these topics and the robot model by running the command below in a new terminal.
Then you can save the current image by right-clicking on the display window. By deafult, images will be saved as frame000.jpg, frame000.jpg, etc. Note, that the image will be saved to the terminal's current work directory.
**OPTION 2:** Use the `image_saver` node to save an image to the terminals current work directory.
In this section, you can use a Python node to capture an image from the RealSense camera. Run the following commands to save a .jpeg image of the image topic */camera/color/image_raw_upright_view*.
In this section, you can use a Python node to capture an image from the [RealSense camera](https://www.intelrealsense.com/depth-camera-d435i/). Run the following commands to save a .jpeg image of the image topic */camera/color/image_raw_upright_view*.
```bash
# Terminal 4
cd ~/catkin_ws/src/stretch_tutorials/src
python3 capture_image.py
```
An image named **camera_image.jpeg** is saved in the **stored_data** folder in this package.
### The Code
@ -115,10 +109,8 @@ if __name__ == '__main__':
rospy.init_node('capture_image', argv=sys.argv)
CaptureImage()
rospy.spin()
```
### The Code Explained
Now let's break the code down.
@ -134,14 +126,12 @@ import sys
import os
import cv2
```
You need to import rospy if you are writing a ROS Node. There are functions from sys, os, and cv2 that are required within this code. cv2 is a library of Python functions that implements computer vision algorithms. Further information about cv2 can be found here: [OpenCV Python](https://www.geeksforgeeks.org/opencv-python-tutorial/).
You need to import `rospy` if you are writing a ROS [Node](http://wiki.ros.org/Nodes). There are functions from sys, os, and cv2 that are required within this code. cv2 is a library of Python functions that implements computer vision algorithms. Further information about cv2 can be found here: [OpenCV Python](https://www.geeksforgeeks.org/opencv-python-tutorial/).
```python
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError
```
The `sensor_msgs.msg` is imported so that we can subscribe to ROS `Image` messages. Import [CvBridge](http://wiki.ros.org/cv_bridge) to convert between ROS `Image` messages and OpenCV images.
Join the directory and file name using the `path.join()` function. Then use the `imwrite()` function to save the image.
```python
rospy.signal_shutdown("done")
sys.exit(0)
```
The first line of code initiates a clean shutdown of ROS. The second line of code exits the Python interpreter.
```python
rospy.init_node('capture_image', argv=sys.argv)
CaptureImage()
```
The next line, `rospy.init_node(NAME, ...)`, is very important as it tells rospy the name of your node -- until rospy has this information, it cannot start communicating with the ROS Master. In this case, your node will take on the name talker. NOTE: the name must be a base name, i.e. it cannot contain any slashes "/".
The next line, `rospy.init_node(NAME, ...)`, is very important as it tells rospy the name of your node -- until rospy has this information, it cannot start communicating with the ROS Master. **NOTE:** the name must be a base name, i.e. it cannot contain any slashes "/".
Instantiate the class with `CaptureImage()`
Instantiate the `CaptureImage()` class.
```python
rospy.spin()
```
Give control to ROS. This will allow the callback to be called whenever new
messages come in. If we don't put this line in, then the node will not work,
and ROS will not process any messages.
Give control to ROS. This will allow the callback to be called whenever new messages come in. If we don't put this line in, then the node will not work, and ROS will not process any messages.
## Edge Detection
@ -214,7 +197,6 @@ In this section, we highlight a node that utilizes the [Canny Edge filter](https
cd ~/catkin_ws/src/stretch_tutorials/src
python3 edge_detection.py
```
The node will publish a new Image topic named */image_edge_detection*. This can be visualized in RViz and a gif is provided below for reference.
<palign="center">
@ -233,7 +215,6 @@ import cv2
from sensor_msgs.msg import Image
from cv_bridge import CvBridge, CvBridgeError
class EdgeDetection:
"""
A class that converts a subscribed ROS image to a OpenCV image and saves
@ -300,7 +281,6 @@ Convert the cv2 image back to a ROS image so it can be published.
image_msg.header = msg.header
self.pub.publish(image_msg)
```
Publish the ROS image with the same header as the subscribed ROS message.
Alan G. Sanchez
2 years ago