Standard messages, scalar fallbacks and descriptor mappings

Availability

Use the current published main source. After updating, rebuild, source the workspace and restart affected ROS processes as described in Install and build. Importing a viewer layout does not update an installed driver. Automatic Illuminance/scalar outputs work without a ROS mapping block; optional descriptor selection uses ros.version: 1 below.

These declarations affect measurement publishers. Servo-angle and LED-colour command subscriptions have their own standard-message contracts in Servo and LED command topics.

Find the actual outputs

In a terminal with the same ROS environment, domain and middleware as the driver:

ros2 topic list -t --no-daemon
BOARD_NS='PASTE_DISCOVERED_BOARD_NAMESPACE_HERE'
ros2 topic echo "$BOARD_NS/devices" std_msgs/msg/String \
  --qos-reliability reliable --qos-durability transient_local \
  --qos-depth 1 --full-length --once

Replace BOARD_NS with the complete namespace from /axiom_discovery/boards, including its leading slash. Variables are local to the terminal where you set them. The board inventory's topic is a relative sensor root. public_topics[group][suffix] gives its actually published relative outputs; prepend the board namespace to use them as full ROS paths. Unresolved rows have topic: null.

The parallel output_info[group][suffix] map records each published canonical output's message_type and unit. For example, this is an excerpt from a resolved LTR-390 row, using an illustrative bus/address:

{
  "topic": "ltr_2d390_b1_53",
  "public_topics": {
    "x": {
      "ambient": "ltr_2d390_b1_53/ambient",
      "UVI": "ltr_2d390_b1_53/UVI"
    }
  },
  "output_info": {
    "x": {
      "ambient": {"message_type": "sensor_msgs/msg/Illuminance", "unit": "lux"},
      "UVI": {"message_type": "std_msgs/msg/Float64", "unit": "index"}
    }
  }
}

The full row also includes generic outputs and device identity/state fields. Group x is the ordinary payload group; other groups have separate paths. A null unit means unspecified/unitless or no single measurement unit, for example an IMU with several physical quantities. Outputs appear after their first published sample and retire with their publishers. Alias paths are listed separately; an alias that reserves a canonical path can suppress that canonical output. See sensor names, lifetime and aliases.

Illuminance and LTR-390

With the existing LTR-390 descriptor, ambient publishes sensor_msgs/msg/Illuminance in lux and UVI publishes std_msgs/msg/Float64 in the descriptor's index unit. No optional ROS block is needed. Attribute case is retained: UVI and uvi are different suffixes.

For example, a board named /axiom might publish /axiom/ltr_2d390_b1_53/ambient and /axiom/ltr_2d390_b1_53/UVI. These are examples; copy your actual complete topic paths:

LIGHT_TOPIC='PASTE_FULL_ILLUMINANCE_TOPIC_HERE'
UV_TOPIC='PASTE_FULL_UVI_TOPIC_HERE'
ros2 topic type "$LIGHT_TOPIC"
ros2 topic echo "$LIGHT_TOPIC" sensor_msgs/msg/Illuminance \
  --once --qos-reliability best_effort
ros2 topic type "$UV_TOPIC"
ros2 topic echo "$UV_TOPIC" std_msgs/msg/Float64 \
  --once --qos-reliability best_effort

Read illuminance for lux and data for UVI. Illuminance carries the sample's timestamp and configured sensor frame; variance: 0 means the variance is unknown. Negative or unavailable illuminance is NaN, not a measured zero. UVI has no header or unit field; use inventory for its unit and sample for measurement timing and validity.

Automatic Illuminance mapping recognises scalar attributes named ambient, als, white, visible, illuminance or light (case insensitive), with a known lux conversion. The rule applies across compatible profiles rather than only one sensor model. A channel such as ir stays a numeric fallback even if its descriptor labels it lux; that label alone does not identify a photometric light quantity.

Scalar fallbacks

The decoder already applies masks, divisors, offsets and other descriptor transforms. The ROS adapter does not apply them twice or replace an unavailable reading with a raw counter. Unknown units stay unknown. A unit such as index, ppm or ticks is not silently relabelled as another physical quantity. Numeric scalars use Float64 even when the wire field is an integer, because the engineering result may be fractional. Integer values above 2^53 can lose Float64 precision; sample retains the raw value.

By default, existing semantic/compound adapters consume the attributes they represent. IMU axes, range values, temperature/humidity, servo position, battery voltage and image pixels/dimensions are not also published as automatic scalar copies. Other fields, such as status, counters and auxiliary readings, may get scalar topics. Generic sample and data still contain the full decoded row.

Float64, Bool and String carry only data, with no measurement timestamp, frame or unit field. A headerless fallback is useful for plotting a value, but use sample when timing, validity or raw/decoded values matter. sample.values_json contains raw, engineering and SI values, their units and validity; data is a JSON convenience view. Retain device_metadata with a recording when you need the complete decoder profile.

Aliases and repeated sensor types

Automatic paths retain model, bus and address, so multiple sensors of the same type stay distinct. Fallback suffixes retain attribute case and escape unsafe characters. A name that would be hidden, start with a digit or collide with reserved adapter output names gains an attribute_ prefix; for example, a numeric attribute named data publishes as attribute_data. Read the actual suffix from inventory.

Aliases choose an existing output; they do not change its message type or install a profile. Merge this fragment into the intended board's existing settings, retaining its connection/identity configuration:

    topic_aliases:
      light: {type: LTR-390, source: ambient}
      uv: {type: LTR-390, source: UVI}

For an illustrative /axiom board, these add /axiom/light and /axiom/uv. An alias binds only when exactly one matching sensor is online, resolved and fresh. If several LTR-390 sensors match, add string bus and address selectors copied from inventory, or use their distinct canonical paths. Header-bearing aliases retain the same timestamp/frame; headerless aliases remain headerless. Canonical and alias QoS overrides match exact topic paths. Restart affected processes after changing read-only board configuration.

Plot the values in Foxglove

Start the bridge and connect the viewer using the Foxglove scalar plotting instructions. Choose numeric fields directly: Illuminance uses .illuminance, Temperature uses .temperature, RelativeHumidity uses .relative_humidity and Float64 uses .data. These outputs do not require extracting numbers from JSON strings. Use separate plots for different units and label their axes accordingly.

Troubleshooting

Continue with Sensors and multiple boards or Foxglove dashboards.