Add derivative filter and discretization

[ViktorCVS]

Overview

Adds a configurable derivative filter. It also introduces separate discretization method selectors for the I and D terms. Forward Euler remains the default to preserve existing behavior.

What was added/changed in this PR

• Added a first-order derivative filter (tf) applied to the D term.
• Introduced per-term discretization selectors: i_method and d_method (e.g., "forward_euler", "backward_euler", "trapezoidal"), with "forward_euler" as the default.
• Implemented discrete D-term updates for the supported methods, including filtered forms; falls back to unfiltered behavior when tf == 0.
• Added internal state (d_term_last_, d_error_last_, i_term_last_, aw_term_last_) to support trapezoidal (Tustin) and filtered updates.

About tests

The packages compile correctly and have passed the pre‑commit and colcon tests. New tests are being added based on formula values to compare with those from compute_command.

Related PR's

• Add derivative filter and discretization methods ros2_controllers#1909

Attachments

Full derivation of the discrete-time PID used in this PR. The document shows the step-by-step development of the equations.

ros2_control_new_discretization_feature.pdf

Why is this a draft?

• Some tests are still missing. I’ve already started adding them.
• Existing tests need to be adjusted to accommodate the new parameters.

Final notes

I'm very open to any recommendations to improve this code.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 79.89130% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.93%. Comparing base (534eaf3) to head (7c62e5a).

Files with missing lines	Patch %	Lines
control_toolbox/src/pid.cpp	60.75%	28 Missing and 3 partials ⚠️
control_toolbox/include/control_toolbox/pid.hpp	69.23%	3 Missing and 1 partial ⚠️
control_toolbox/src/pid_ros.cpp	92.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           ros2-master     #471      +/-   ##
===============================================
+ Coverage        78.86%   78.93%   +0.06%     
===============================================
  Files               29       29              
  Lines             1893     2046     +153     
  Branches           119      123       +4     
===============================================
+ Hits              1493     1615     +122     
- Misses             332      362      +30     
- Partials            68       69       +1     

Flag	Coverage Δ
unittests	78.93% <79.89%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ontrol_toolbox/include/control_toolbox/pid_ros.hpp	100.00% <ø> (ø)
control_toolbox/test/pid_ros_parameters_tests.cpp	100.00% <100.00%> (ø)
control_toolbox/test/pid_tests.cpp	100.00% <100.00%> (ø)
control_toolbox/src/pid_ros.cpp	70.37% <92.00%> (+2.50%)	⬆️
control_toolbox/include/control_toolbox/pid.hpp	61.36% <69.23%> (+0.38%)	⬆️
control_toolbox/src/pid.cpp	72.58% <60.75%> (-11.16%)	⬇️

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[ViktorCVS]

Hi, @christophfroehlich! I still need to fix the existing tests and add new ones. However, the equations are quite large, and the compute_command function has grown a lot. Do you think it’s acceptable (with better organization), or should something be changed?

[christophfroehlich]

Hi, @christophfroehlich! I still need to fix the existing tests and add new ones. However, the equations are quite large, and the compute_command function has grown a lot. Do you think it’s acceptable (with better organization), or should something be changed?

IMHO it is acceptable to go further in this direction, thanks!