Piksi ROS

A python based driver for SwiftNav's Piksi RTK GPS modules.

Features:

• Publishes:
  • NavSatFix (separate ones for RTK fix and SPP fix)
  • Odometry (with positioning from RTK data)
  • TimeReference
  • as well as custom Observations and Ephemeris msgs.
• Can send/receive observations from another Piksi through UDP or Serial (for setups that don't use the external radios)
• Supports setting any of the settings on the piksi at startup (saving to flash is optional)
• Can publish TF transforms from UTM->base_station and/or base_station->rover
• Supplies diagnostic info.
• Keeps track of fix mode through watchdog timers.
• Dynamic reconfigure support.

Published Topics:

• ~fix (sensor_msgs/NavSatFix). Best fix available.
• ~spp_fix (sensor_msgs/NavSatFix). Single point precision fix.
• ~rtk_fix (sensor_msgs/NavSatFix). RTK fix (when available).
• ~odom (nav_msgs/Odometry). RTK based odometry.
• ~time (sensor_msgs/TimeReference). GPS clock (does not match UTC as it does not account for leap seconds)
• ~observations (piksi_ros/Observations). Satellite observations. Enable through publish_observations parameter.
• ~ephemeris (piksi_ros/Ephemeris). Satellite observations. Enable through publish_ephemeris parameter.

Parameters:

Parameters with * can be changed through dynamic reconfigure.

Piksi stuff:

• port - The serial port device of the Piksi unit. Default: /dev/ttyUSB0.
• baud_rate - Baud rate for the serial port. Default: 1000000.

Piksi hardware settings:

You can have the driver set settings on the piksi at startup. Settings are not committed to device flash unless piksi_save_settings is set appropriately.

• piksi/SECTION/SETTING - Possible SECTION and SETTING values can be found in Piksi documentation or in the piksi console (subset can be found in piksi_settings.yaml). *
• piksi_save_settings - Commits piksi settings to device flash if set true. Default: false.

The piksi settings as they were on driver startup can be accessed through the parameter server under ~piksi_original_settings/.

Frames:

• frame_id - Frame id for GPS messages. Default: piksi
• rtk_frame_id - Frame id for the base. Default: rtk_gps
• utm_frame_id - Frame id for an UTM coordinate frame. Default: utm
• child_frame_id - Frame id for the rover (typically base_link or base_link_stabilized). Default: base_link

Publish settings:

• publish_utm_rtk_tf - Publish utm_frame_id->rtk_frame_id transform. Default: False
• publish_rtk_child_tf - Publish rtk_frame_id->child_frame_id transform. Default: False
• publish_observations - Publish observations (list of tracked satellites and related measurements). Default: False
• publish_ephemeris - Publish ephemeris information. Default: False

Driver settings:

• rtk_fix_timeout - Time to wait from last RTK message received until switching to SPP positions for best fix. Default: 0.2 *
• spp_fix_timeout - Time to wait from last SPP message receveid until declaring no-fix. Default: 1.0 *
• rtk_h_accuracy - RTK horizontal sddev. Default: 0.04 *
• rtk_v_accuracy - RTK vertical sddev. Default: 0.12 *

Diagnostics:

• diag/heartbeat_freq - Expected frequency for heartbeats. Default: 1.0
• diag/update_freq - Expected update frequency. Default: 10.0
• diag/freq_tolerance - Frequency tolerance. Default: 0.1
• diag/window_size - Diagnostics window size. Default: 10
• diag/min_delay - Min timestamp delay for topics. Default: 0.0
• diag/max_delay - Max timestamp delay for topics. Default: 0.2

Observation sending/receiving:

• obs/udp/send - Whether to send observations received from Piksi through UDP. Default: False

• obs/udp/receive - Whether to receive observations through UDP and forward to Piksi. Default: False

• obs/udp/host - UDP host/ip. Leave blank for receiver for easier configuration. Default: ''

• obs/udp/port - UDP port to use. Default: 50785

• obs/serial/send - Whether to send observations received from Piksi through a serial port. Default: False

• obs/serial/receive - Whether to receive observations through a serial port and forward to Piksi. Default: False

• obs/udp/port - Serial port. Default: ''

• obs/udp/baud_rate - Serial port baud rate. Default: 115200

Other:

• sbp_log_file - Specify a log file to log all incoming SBP packets from Piksi to. Default: ''
• debug - Enable extra debug messages. Default: False

Published transforms

The following transforms are published if configured to do so:

• utm_frame_id -> rtk_frame_id
• rtk_frame_id -> child_frame_id

Issues/notes:

• Covariance info is either set by parameters or set by a hack. It does not reflect an instantanious estimate of the covariance.
• No error-checking when setting parameters.

Todo:

• Add/improve covariance estimate for published data.
• Rewrite in C++