exercises.md

Exercises

Ten functions to implement from scratch. They are the same ten in both languages, checked by the same expectations, so pick whichever you think in.

Python	C++
python/exercises/exercises.py	cpp/exercises/exercises.cpp

The rules

• Use NumPy (or plain C++). Do not call OpenCV — writing the maths yourself is the entire point.
• Do not import camintrinsics either; that is just copying the answer.
• Every function has a worked answer in solutions.py / solutions.cpp. Look after you have tried, and compare approaches rather than diffing text.

Conventions are the repository's own: camera down +Z, xy is normalized, uv is pixels, point arrays are (N, 2) or (N, 3).

The list

#	Function	Does	Chapter
1	ex01_build_K	Assemble K from fx, fy, cx, cy, skew	2
2	ex02_project_pinhole	Project 3D points to pixels; Z <= 0 must give NaN	1
3	ex03_distort	Apply the plumb-bob model in normalized coordinates	3
4	ex04_fov_degrees	Horizontal and vertical field of view from K	2
5	ex05_K_after_resize	Update K for a resized image	4
6	ex06_K_after_crop	Update K for a cropped image	4
7	ex07_undistort_point	Invert exercise 3 — the hard one	5
8	ex08_K_from_hfov	Build a centred, square-pixel K from a field of view	2
9	ex09_classify_distortion	Barrel, pincushion or none at a given radius	3
10	ex10_pipeline_K	Crop then resize — the one that bites in production	4

Exercise 7 is where people learn something they did not expect: the obvious fixed-point iteration does not always converge. Chapter 5 explains why, and the verification notes record what this repository does instead.

Checking your work

Python

uv run python/exercises/check.py               # scorecard for all ten
uv run python/exercises/check.py 3 7           # only exercises 3 and 7
uv run python/exercises/check.py --solutions   # verify the reference answers
uv run pytest                                  # the same checks under pytest

C++

./cpp/build/bin/check_exercises                # scorecard for all ten
./cpp/build/bin/check_exercises 3 7            # only exercises 3 and 7
./cpp/build/bin/check_exercises --solutions    # verify the reference answers
ctest --test-dir cpp/build                     # the same, as a test

An exercise you have not written yet is reported as not implemented yet, not as a failure, so the scorecard is readable from the very first run.

When you have finished, take the quiz.