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docs: laser.md article
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sfalexrog
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# Working with a laser rangefinder
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## Rangefinder VL53L1X
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## VL53L1X Rangefinder
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The rangefinder model recommended for Clever is STM VL53L1X. This rangefinder can measure distances from 0 to 4 m while ensuring high measurement accuracy.
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### Connecting to Raspberry Pi
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> **Note** For correct operation of a laser rangefinder with a flight countroller <a id="download-firmware" href="https://github.com/CopterExpress/Firmware/releases">custom PX4 firmware</a> is needed. See more about firmware in [corresponding article](firmware.md).
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> **Note** You need to flash a <a id="download-firmware" href="https://github.com/CopterExpress/Firmware/releases">custom PX4 firmware</a> on your flight controller for the rangefinder to work correctly. See more about firmware in the [corresponding article](firmware.md).
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<script type="text/javascript">
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fetch('https://api.github.com/repos/CopterExpress/Firmware/releases').then(res => res.json()).then(function(data) {
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});
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</script>
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Connect the rangefinder to pins 3V, GND, SCL and SDA via the I²C interface:
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Connect the rangefinder to the 3V, GND, SCL and SDA pins via the I²C interface:
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<img src="../assets/raspberry-vl53l1x.png" alt="Connecting VL53L1X" height=600>
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If the pin marked GND is occupied, you can use another free one using the [pinout](https://pinout.xyz).
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If the pin marked GND is occupied, you can use any other ground pin (look at the [pinout](https://pinout.xyz) for reference).
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> **Hint** Via the I²C interface, you can connect several peripheral devices simultaneously. For this purpose, use a parallel connection.
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> **Hint** You can connect several peripheral devices via the I²C interface simultaneously. Use a parallel connection for that.
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### Enabling
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### Enabling the rangefinder
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[Connect via SSH](ssh.md) and edit file `~/catkin_ws/src/clever/clever/launch/clever.launch` so that driver VL53L1X is enabled:
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[Connect via SSH](ssh.md) and edit file `~/catkin_ws/src/clever/clever/launch/clever.launch` so that the VL53L1X driver is enabled:
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```xml
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<arg name="rangefinder_vl53l1x" default="true"/>
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```
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By default, the rangefinder driver sends the data to Pixhawk (via topic `/mavros/distance_sensor/rangefinder_sub`). To view data from the topic, use command:
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By default, the rangefinder driver sends the data to Pixhawk via the `/mavros/distance_sensor/rangefinder_sub` topic. To view data from the topic, use the following command:
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```(bash)
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```bash
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rostopic echo mavros/distance_sensor/rangefinder_sub
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```
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### PX4 settings
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To use the rangefinder data in [PX4 must be configured](px4_parameters.md).
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PX4 should be properly [configured](px4_parameters.md) to use the rangefinder data.
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When using EKF2 (`SYS_MC_EST_GROUP` = `ekf2`):
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Set the following parameters when EKF2 is used (`SYS_MC_EST_GROUP` = `ekf2`):
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* `EKF2_HGT_MODE` = `2` (Range sensor) – when flying over horizontal floor;
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* `EKF2_HGT_MODE` = `2` (Range sensor) – for flights over horizontal floor;
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* `EKF2_RNG_AID` = `1` (Range aid enabled) – in other cases.
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When using LPE (`SYS_MC_EST_GROUP` = `local_position_estimator, attitude_estimator_q`):
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Set the following parameters when LPE is used (`SYS_MC_EST_GROUP` = `local_position_estimator, attitude_estimator_q`):
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* The "pub agl as lpos down" flag is ticked in the `LPE_FUSION` parameter – when flying over horizontal floor.
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* The "pub agl as lpos down" flag should be set in the `LPE_FUSION` parameter – for flights over horizontal floor.
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### Obtaining data from Python
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### Receiving data in Python
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To obtain data from the topic, create a subscriber:
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In order to receive data from the topic, create a subscriber:
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```python
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from sensor_msgs.msg import Range
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@@ -66,7 +66,7 @@ from sensor_msgs.msg import Range
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# ...
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def range_callback(msg):
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# Processing new data from the rangefinder
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# Process data from the rangefinder
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print 'Rangefinder distance:', msg.range
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rospy.Subscriber('mavros/distance_sensor/rangefinder_sub', Range, range_callback)
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@@ -74,13 +74,13 @@ rospy.Subscriber('mavros/distance_sensor/rangefinder_sub', Range, range_callback
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### Data visualization
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To build a chart using the data from the rangefinder, one can use rqt_multiplot.
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You may use rqt_multiplot tool to plot rangefinder data.
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rviz may be used for data visualization. To do this, add a topic of the `sensor_msgs/Range` type to visualization:
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<img src="../assets/rviz-range.png" alt="Range in rviz">
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See [read more about rviz and rqt](rviz.md).
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Read more [about rviz and rqt](rviz.md).
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<!--
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### Connecting to Pixhawk / Pixracer
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