Sequencer

Role

The Sequencer module orchestrates automatic acquisition for an astrophotography session. It executes a list of sequence lines, each defining the frame type, filter, exposure, gain, offset, and number of images to acquire. FITS files are saved automatically into a folder tree organised by object, frame type, and filter.

Required devices

Device	Role
Camera	Image acquisition
Filter wheel	Optional — used if configured

Sequence structure

A sequence is made up of several lines. Each line defines:

Column	Description
Frame type	Light (L), Bias (B), Dark (D), or Flat (F)
Filter	Filter selected from the filter wheel
Exposure	Exposure duration in seconds
Count	Number of images to acquire for this line
Gain	Camera gain
Offset	Camera offset
Progress	Completion status of the current line

Lines are executed in order, from first to last.

Parameters

Object

Parameter	Description
Name	Name of the imaged object — used to name the save folder
RA	Right ascension of the object
DEC	Declination of the object

Slave modules

The sequencer can interact with other modules for focusing and guiding.

Parameter	Description
Focus module instance	Name of the Focuser module instance to use (e.g. `focus`)
Guider module instance	Name of the Guider module instance to use (e.g. `guider`)

Automation parameters

Parameter	Description
Auto-focus at sequence start	Automatically triggers a focus run before the first sequence line (using the first line’s filter)
Auto-focus on filter change	Automatically triggers a focus run on each filter change (Light and Flat frames only)
Suspend guiding during focus	Pauses guiding before the focus run and resumes it afterwards
Resume guiding settle time (s)	Wait time in seconds after guiding resumes, to allow it to stabilise before acquisitions continue

Algorithm

Sequence start

Connect to the camera and reset the frame
Mark all lines as Queued
If Auto-focus at sequence start is enabled and the first frame is Light or Flat: focus with the first line’s filter, then start
Otherwise: start the first line immediately

Line execution

For each line of the sequence:

Select the filter on the filter wheel
If the filter changed and Auto-focus on filter change is enabled: trigger auto-focus (and suspend/resume guiding if configured)
Configure the frame type on the camera (Light, Bias, Dark, Flat)
Create the destination folder
Acquire the defined number of images one by one

File saving

FITS files are saved in the following folder tree:

<object>/
  LIGHT/
    <filter>/   ← Light frames
  FLAT/
    <filter>/   ← Flat frames
  BIAS/         ← Bias frames
  DARK/         ← Dark frames

Each file name includes the object name, frame type, filter, and a timestamp.

Integration with the Focus module

When an auto-focus is requested:

The sequencer sends the autofocus action to the designated Focuser module
It pauses acquisitions and waits for the focus run to complete
If Suspend guiding is enabled, it sends abortguider to the Guider module before focusing, then guide afterwards
If a settle time is configured, it waits that delay before resuming

Progress

Indicator	Description
Sequence	Global progress: number of lines processed out of the total
Current exposure	Progress of the current exposure (0 to 100 %)
Per-line progress	Number of images acquired out of the total for each line

Actions

Action	Description
Start sequence	Starts executing the sequence from the first line
Abort	Immediately stops the current sequence