Support custom sensors

[osrf-migration]

Original report (archived issue) by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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Summary

Downstream users often need to create their own custom sensors. Ideally, they should be able to leverage Ignition Sensors' APIs for that.

Motivation

Users need the flexibility to implement sensors that don't make it into the Ignition Sensors library, because they want to keep the sensors private, or because the sensors are too specialized for some use case, or some other reason.

Describe alternatives you've considered

Users could always implement their sensors as custom Ignition Gazebo systems, but they wouldn't be able to make use of Ignition Sensors' features like custom noise and other convenient APIs.

Additional context

Ignition sensors already has a plugin architecture and each sensor is being released as its own component package. But we don't have any examples of a sensor implemented as an external library. Is that already supported? What's missing?

[peci1]

How would custom sensors be represented in SDF? Is that possible at all?

[chapulina]

How would custom sensors be represented in SDF? Is that possible at all?

Here's a proposal for custom attributes and elements that's in the works and could come in handy here: http://sdformat.org/tutorials?tut=custom_elements_attributes_proposal

[chapulina]

Addressed in #100

[chapulina]

This will be available from Ignition Fortress (v6). See the tutorial here: https://github.com/ignitionrobotics/ign-sensors/blob/main/tutorials/custom_sensors.md