9e1258440b
Documents the extrinsic vs intrinsic semantics of `plus()` and `minus()`. (`rotateBy()` was documented in [a previous PR](https://github.com/wpilibsuite/allwpilib/pull/5508)) Fixes usage of `plus()` and `minus()` in `Rotation3d.interpolate()`. (Fixes #8523) Fixes incorrect usages of `plus()`, `minus()`, and `rotateBy()` throughout `Odometry3d`. Adds explanatory comments for some `plus()`, `minus()`, and `rotateBy()` operations. Fixes `TimeInterpolatableBuffer` not using twists for `Pose3d` (this was just because I happened to notice it, it isn't really related to the PR) To check all of our usages of `plus()`, `minus()`, and `rotateBy()`, I marked them as deprecated, checked compile errors from `./gradlew compileJava`, and then undeprecated them. You can see all of the spots that showed up (at least on the Java side) by viewing the diff for 241109c. I wanted to present this alternative to #8526 because the change has its own quirks, there's little time before kickoff, and there would be no code-side warning to teams (and mentors) already used to the current behavior.
wpimath
wpimath contains utilities for robot control (feedforward/feedback), state estimation (filters, Kalman and otherwise), 2D/3D geometry, kinematics, trajectory generation, and trajectory optimization.
Implementation guidelines
A lot of wpimath features directly implement equations from books or papers. The following guidelines make that code easier to maintain and audit for correctness.
Citations
Cite source books/papers at the top of the function (e.g., See section 5.6 of "book name".). If multiple items from a given work are referenced, write a bibliography entry for the work to reference later.
Cite the equation numbers each line of code implements, if applicable. For example, See equation (#.#) of [1]. where [1] is a bibliography reference number.
Comments
Comment each line of code with its pretty-printed math equivalent.
// xₖ₊₁ = Axₖ + Buₖ
x = A * x + B * u;
Link to explanatory material where appropriate to explain background knowledge and/or notation choice.
Variable naming
Follow established mathematical convention where possible (e.g., use A, B, C, D for state-space notation instead of stateTransitionMatrix).
Use math symbols in variable names (see Unicodeit) to match source papers. This usually entails some Greek letters (α), but diacritics, superscripts, and subscripts need to be spelled out (ẋ → x_dot, αₖ² → α_k_sq) since compilers reject them, and the small features make variable names difficult to read.
Derivations
Put small derivations in comments within the function. Put large derivations in algorithms.md and link to them.
Unicodeit
When writing math expressions in documentation, use https://www.unicodeit.net/ to convert LaTeX to a Unicode equivalent that's easier to read. Not all expressions will translate (e.g., superscripts of superscripts) so focus on making it readable by someone who isn't familiar with LaTeX. If content on multiple lines needs to be aligned in Doxygen/Javadoc comments (e.g., integration/summation limits, matrices packed with square brackets and superscripts for them), put them in @verbatim/@endverbatim blocks in Doxygen or <pre> tags in Javadoc so they render with monospace font.
The LaTeX to Unicode conversions can also be done locally via the unicodeit Python package. To install it, execute:
pip install --user unicodeit
Here's example usage:
$ python -m unicodeit.cli 'x_{k+1} = Ax_k + Bu_k'
xₖ₊₁ = Axₖ + Buₖ
On Linux, this process can be streamlined further by adding the following Bash function to your .bashrc (requires wl-clipboard on Wayland or xclip on X11):
# Converts LaTeX to Unicode, prints the result, and copies it to the clipboard
uc() {
if [ $WAYLAND_DISPLAY ]; then
python -m unicodeit.cli $@ | tee >(wl-copy -n)
else
python -m unicodeit.cli $@ | tee >(xclip -sel)
fi
}
Here's example usage:
$ uc 'x_{k+1} = Ax_k + Bu_k'
xₖ₊₁ = Axₖ + Buₖ