caelumA capture stack for allsky cameras

Headless capture engine, closed-loop exposure control driven by real sun and moon geometry, RAM-first image pipeline, and a self-healing upload path to a permanent remote archive.

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Core concepts

Exposure follows the sky, not a clock

Sun altitude from an offline astropy ephemeris classifies the sky into five periods. Each period has its own exposure and gain envelope, and a closed feedback loop drives the camera inside it. The camera's own auto-exposure is always disabled.

Three camera backends, one pipeline

picamera2 for Raspberry Pi camera modules, OpenCV/V4L2 for any UVC webcam, and a synthetic mock backend so the whole stack runs on a laptop with no hardware attached. Switching backends changes nothing downstream.

RAM-first capture path

The capture thread owns the camera and does nothing but capture, calibrate, measure, thumbnail, publish. Disk writes, derivative processing and uploads all subscribe to an event bus and run off-thread, so capture cadence never depends on how busy the rest of the system is.

Keograms and meteor detection

Two built-in derivative workers ship with the engine — a daily keogram assembled column by column with a live partial flush during the night, and a frame-difference streak detector that annotates frames and emits crops.

Self-healing upload

rsync pushes today's directories often and reconciles the whole tree periodically. rsync does its own diffing, so there is no retry ledger to corrupt — a reboot mid-transfer or a dead uplink resolves itself on the next reconciliation pass.

Plugins without forking

A plugin is a class with four optional hooks and a config block carrying enabled, order and an opaque settings dict. Built-in derivative workers use exactly the same interface, so the extension point is proven by the code that ships with it.