Use picamera2 from venv

[sonnyp]

As discussed with @ethanjli in a 2025-04-02 one-on-one software meeting.

However on Fedora at least, it builds the packages from source and I had to install python3-devel and libcap-devel so I'm not sure we can do what's proposed here on RPI. End of day, will dig and test.

Todo

• revert os: Upgrade python3-libcamera to fix issue on bookworm fairscope/PlanktoScope#551

[sonnyp]

@ethanjli

regarding

poetry tries to build them from source instead of installing the armv7l wheels. Maybe poetry is messing up at detecting the machine platform or something.

Is that a big deal? I also noticed a couple of related things in install scripts

https://www.piwheels.org/ doesn't support 64 bits Raspberry OS anyway so I think we should assume some dependencies might be compiled from source and just count on things to get better over time ?

On the other hand picamera2 recommends installing from apt https://github.com/raspberrypi/picamera2?tab=readme-ov-file#installation

My suggestion would be to use picamera2 from apt (and anything else that we consider as part of the "Raspberry OS runtime") and the rest from pypy/piwheels without workarounds to avoid compiling from source.

[ethanjli]

Is that a big deal

It used to be a bigger deal because of the impact on the OS setup scripts used to take ~30 minutes to run on an actual booted RPi - but now that we're building OS images in arm64 runners on GitHub Actions (as of fairscope/PlanktoScope#520), we might be able to tolerate building a few small hardware-related packages from source if they have minimal impact on OS image build times. But "aesthetically" I'd prefer to avoid building packages from source. So I consider this a "small-to-medium-sized deal".

https://www.piwheels.org/ doesn't support 64 bits Raspberry OS anyway

As of #74 (which was the first PR made after the stable release of v2024.0.0, which is the first stable release with deprecation of 32-bit OS support), we no longer provide the option to download pre-built 32-bit wheels from piwheels. Instead, we rely on PyPI for pre-built 64-bit wheels.

My suggestion would be to use picamera2 from apt (and anything else that we consider as part of the "Raspberry OS runtime") and the rest from pypy/piwheels without workarounds to avoid compiling from source.

Yes, since the picamera2 Python package is coupled to libcamera, managing picamera2 in a venv still leaves libcamera outside the realm of what we can manage via poetry/venv. Relying on picamera2 from apt is our current practice and I think it's reasonable to continue this way (which if I understand correctly would mean that we just close this PR). If we do that and close this PR, I'd prefer to have a follow-up PR for fairscope/PlanktoScope#551 which implements option 1 as described in fairscope/PlanktoScope#551 (comment)

[sonnyp]

We decided to

• keep using picamera2 @ethanjli
• update this PR to drop unnecessary dependencies @sonnyp

[sonnyp]

• Simplify dependencies #81
• backend: Simplify dependencies fairscope/PlanktoScope#564