The Ekos Scheduler is an important component of your imaging workflow. It connects to INDI, starts and stops all the other Ekos modules, schedules jobs according to their constraints and priorities, monitors those jobs as they execute, and then safely brings down the system when jobs are done, or before dawn. Whether you are running multi-day imaging sessions for multiple targets, or simply trying to image a single target for a few hours, it is advisable to have the Scheduler control your imaging sessions.

The heart of the Scheduler is a table displaying the list of Scheduler jobs the user wants to run. Associated with each jobs are attributes (mostly described in the settings section below). The attributes describe the name of the job, where the telescope should be pointed when imaging that job, a description of what types of images should be captured, constraints about when the jobs should run (e.g. altitude, twilight, moon, landscape blockages, etc.), things that need to be done before and after the job is run, and strategies for dealing with errors.

You can add, delete, modify or change the order of rows in the Scheduler table.

The Scheduler table (above) lists jobs in order of priority, with higher jobs (on lower-numbered rows) having higher priority than jobs further down the list (with higher-numbered rows).

The Scheduler regularly plans (and re-plans) which jobs should be run, and when. It can start executing a given job, and then later preempt that job for a new one. It can become idle if no jobs can be run (e.g. in daylight), and sleep until such a time that it becomes active again. Its aim is to keep the equipment as busy as possible, while respecting the scheduler-table's priorities. Here's how it works.

When the scheduler starts (or when it replans, which it does every second while active), it looks through the entire list of jobs, starting at the highest priority job, and working its way down to the lowest priority one if necessary. When it finds a job that can run, it starts that job, possibly preempting the currently running job. A jobs can run if its constraints are met, e.g. the target is not blocked by the local terrain, it meets the minimum altitude constraint, it has not already completed all the desired imaging, ...

The algorithm shows its projected next start times and stop times for all job in the Scheduler table. It also shows its estimate of times jobs will run during the next 48 hours in the log panel at the bottom of the window. See the screenshot of the scheduler window at the top of this section.

The scheduling algorithm described in the above paragraph is known as the Greedy Scheduling algorithm. It is the recommended one to use. In previous versions of Ekos, there was another "Classic scheduling algorithm" which is no longer in Ekos. That scheme could not preempt running jobs, and thus did not make as much use of the equipment as the Greedy Algorithm.

There is a checkbox option in the scheduler options menu called Use greedy scheduling which defaults to being checked. The system works as described above when it is checked. When it is unchecked the scheduler is prevented from scheduling lower priority jobs when uncompleted higher priority jobs cannot run. This results in less efficient use of the system, but may give you more control over scheduling.

The scheduler table with its list of jobs and attributes can be saved onto disk and read back in. It writes an .esl file. Controls for writing the current Scheduler table to disk, and reading back other .esl files are located above the table to the right.

Ekos Scheduler provides a simple interface to aid the user in setting the conditions and constraints required for an Scheduler job. You must select the Target, its coordinates, and the Sequence before you can add a job to the Scheduler.

Each Scheduler job is composed of the following:

There are several other options to control how the Scheduler behaves. These are found in the general KStars Settings menu, shown below, in its Ekos tab and Scheduler sub-tab.

It is possible to edit the scheduler's job table, and attributes of individual jobs, while the scheduler is running. As always, you double click on a job, change the desired attributes, and click the checkbox to finalize the change. If you edit the running job it will be restarted (i.e. the startup steps (slew, focus, align, guide) will be re-done. You can also move jobs up and down in priority, add new jobs, or deleted existing ones. You cannot delete the running job.

One important attribute of scheduler jobs is their sequence file (.esq) which controls the capture module while the job is running. For example, it sets number of captures, filters used, gain/ISO, etc. The .esq is normally created and edited in the capture tab, but that cannot be done while the scheduler is running. If you desire to make changes to a .esq file while the scheduler is running, or create a new one, the scheduler provides a tool called the Capture Sequence Editor.

Capture Sequence Editor

The Capture Sequence Editor is a tool to create and edit capture sequence files (.esq) which can be started by clicking the edit (pencil) icon just above the scheduler table. A screenshot is shown below.

The editor is very similar in use and layout to the capture tab--though it is missing all the controls to actually capture image. You edit jobs the same way you do in capture, and load or save sequence queues the same way too (though there are additional Load and Save-To buttons provided in the editor).

Important

It is important to understand that capture sequences rely to some extent on the filterwheel and camera being used (e.g. the filter names, the possible ISO values, ...). The Capture Sequence Editor, which is not connected to the device drivers, does not have direct access to this information. Instead, the editor uses the values from the last time the capture tab connected to its devices. Thus, it may not make sense to try and create a .esq file for a different camera or filterwheel than the last one connected-to. You may need to wait until your scheduler job is completed and edit that .esq directly in the capture tab.

It is also recommended that you don't overwrite .esq files when scheduler jobs are currently using those same files. (It is OK if the scheduler is running, but not running that job.) This can get the scheduler and capture modules out of sync, as they read the files at different times. Instead, you can save to a different filename and then edit the scheduler job to use the new .esq filename.

The description above only tackles the Data Acquisition stage of the observatory workflow. The overall procedure typically utilized in an observatory can be summarized in three primary stages:

Startup procedure is unique to each observatory but may include:

Ekos Scheduler only initiates the startup procedure once the startup time for the first Scheduler job is close (default lead time is 5 minutes before startup time). Once the startup procedure is completed successfully, the scheduler picks the Scheduler job target and starts the sequence process. If a startup script is specified, it shall be executed first.

Depending the on the user selection, the typical workflow proceeds as follows:

Once the Scheduler job is completed successfully, the scheduler selects the next Scheduler job. If no job can be scheduled at this time, the mount is parked until a next job can run. Furthermore, if the next job is not due for a user-configurable time limit, the scheduler performs a preemptive shutdown to preserve resources and performs the startup procedure again when the target is due.

If an unrecoverable error occurs, the observatory initiates shutdown procedure. If there is a shutdown script, it will be executed last.

The following video demonstrates an earlier version of the scheduler, but the basic principles still apply today:

Another critical feature of any remotely operated robotic observatory is weather monitoring. For weather updates, Ekos relies on the selected INDI weather driver to continuously monitor the weather conditions. For simplicity sake, the weather conditions can be summed in three states:

Due to the uniqueness of each observatory, Ekos enables the user to select startup and shutdown scripts. The scripts take care of any necessary procedures that must take place on startup and shutdown stages. On startup, Ekos executes the startup scripts and only proceeds to the remainder of the startup procedure (unpark dome/unpark mount) if the script completes successfully. Conversely, the shutdown procedure begins with parking the mount & dome before executing the shutdown script as the final procedure.

Startup and shutdown scripts can be written any language that can be executed on the local machine. It must return 0 to report success, any other exist value is considered an error indicator. The script's standard output is also directed to Ekos logger window. The following is an sample demo startup script in Python:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import os
import time
import sys

print "Turning on observatory equipment..."
sys.stdout.flush()

time.sleep(5)

print "Checking safety switches..."
sys.stdout.flush()

time.sleep(5)

print "All systems are GO"
sys.stdout.flush()

exit(0)
        

The startup and shutdown scripts must be executable in order for Ekos to invoke them (e.g. use chmod +x startup_script.py to mark the script as executable). Ekos Scheduler enables truly simple robotic operation without the need of any human intervention in any step of the process. Without human presence, it becomes increasingly critical to gracefully recover from failures in any stage of the observation run. Using Plasma™ notifications, the user can configure audible alarms and email notifications for the various events in the Scheduler.

Hubble-like super wide field images of galaxies and nebulae are truly awe-inspiring, and while it takes great skills to obtain such images and process them; many notable names in the field of astrophotography employ gear that is not vastly different from yours or mine. I emphasize vastly because some do indeed have impressive equipment and dedicated observatories worth tens of the thousands of dollars. Nevertheless, many amateurs can obtain stellar wide-field images by combining smaller images into a single grand mosaic.

We are often limited by our camera+telescope Field of View (FOV). By increasing FOV by means of a focal reducer or a shorter tube, we gain a larger sky coverage at the expense of spatial resolution. At the same time, many attractive wide-field targets span multiple FOVs across the sky. Without any changes to your astrophotography gear, it is possible to create a super mosaic image stitched together from several smaller images. There are two major steps to accomplish a super mosaic image:

The 2nd step is handled by image processing applications such as PixInsight, among others, and will not be the topic of discussion here. The first step can be accomplished in Ekos Scheduler where it creates a mosaic suitable for your equipment and in accordance with the desired field of view. Not only Ekos creates the mosaic panels for your target, but it also constructs the corresponding observatory jobs required to capture all the images. This greatly facilitates the logistics of capturing many images with different filters and calibration frames across a wide area of the sky.

The Mosaic Planner in the Ekos Scheduler will create multiple Scheduler jobs based on a central target. To toggle the planner, click on the Mosaic Planner button in Ekos Scheduler or KStars INDI toolbar as illustrated in the screenshot. The planner draws the Mosaic Panel directly unto the sky map. It is recommended to enable HiPS overlay for the best experience. The planner is composed of four stages:

Click Create Jobs to generate mosaic scheduler jobs and add them to the schedule queue. You can further edit the jobs individually, as you would normal Scheduler jobs.