Suggestion: Constraints to use a Horizon file


I know Rowland has raised this with Leonardo separately and some other users have asked for this in separate posts. I thought I would create a specific topic to discuss how to facilitate a description of the issue and suggestions for implementation in case Leonardo and the Voyager team can look at this during Beta testing or for future roll outs.

I use a custom horizon file, basically a text file with AltAz coordinates specifying the minimum altitude of all the objects obstructing my view around my RoR. I originally created it for Cartes du Ciel to correctly specify the Rise and Set times of non-circumpolar objects. When I started using APCC in 2013, it needed a horizon file also to control mount slews. Fortunately the format was exactly the same. APCC itself makes use of this horizon file to report how long an object will be observable for before those slew (and tracking) limits are hit. Those limits change with the DEC so is not as simple as specifying a min and max Hour Angle.

Would it be possible for Advanced to check the Ephemeris of the object being chosen against the AltAz point in the Horizon file to estimate how long to image for? CdC seems to do just this when it reports Rise and Set times.


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Send a format of this file and one example.

All the best

Hi Roberto

I agree this is an important feature for astrophotographer with large amount of obstruction or complex horizon like myself. Without it I have to manually adjust the minimum altitude of each target so it fit my horizon but most cases the east and west horizon limits are very different. So I have to combine other criteria not to shoot at trees.

That’s one of the reasons I asked for a dynamic ephemeris graph in another post so I can adjust target criteria.



Attached is a sample horizon file from APCC. Uploaded as .csv to comply with the forum rules but it’s really a text file with two columns: Az and Alt. No header (commented out).

APCCHorizoSample.hrz.csv (5.5 KB)

This is how APCC displays the horizon internally and how long an object has to run before a limit is reached. See top right box: Time before limit is reached.

Maybe, for AP mounts only, this information can be polled from the application (this is not an ASCOM information field though so not ASCOM compatible).


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Ok, thanks Roberto.

How you create this file ?
Because there are value with comma so not human calculation


APCC has a utility to do so using the mount to track the horizon line and write to file.

BUT any file with those two columns and whole numbers will work. When I created my horizon file for CdC, I just used Excel and saved as .txt.



I used an app called Dioptra to measure my horizon but there are several others. Would be fantastic to have this in Voyager. My south horizon is about 25 degrees but east and west nearer 40. I have to use 49 at the moment to be on the safe side.


I have seen multiple programs that create very similar files. TheSkyX and Sky Tools Imaging both come to mind. If Voyager can accept a CSV file with azimuth, altitude pairs then people should be able to create such a file for upload.

The programs that I’ve used to create one - and I don’t have APCC - let you enter values for <azimuth, minimum altitude>, or move your scope to different points of azimuth and then point it just over the top of the obstacle and click a point to record an <azimuth, altitude> pair at that point. Finally, I’ve used an iPhone app that creates such a file. You stand in one spot and rotate through 360, pointing a cross-hair just above the local horizon obstacles. It records and emails a file with <azimuth, altitude> pairs and then I massage that with Excel into the desired format of TheSkyX or whatever else I’m using that supports a local horizon.

Hope that helps,


I need to define a format for file so ask your help to not create so many imports

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Yes, this would be a fantastic feature for Advanced. I have multiple trees at different altitudes and different azimuth directions. In the Sky X I have a local custom horizon. My previous target planning software would read the Sky X custom horizon and determine when my target was available and for how long.
I could envision a scenario where Robo Targets determines, based on the local horizon file, that the target is only possible in a particular azimuth direction at a altitude higher than a altitude constraint in the target database and uses the local horizon data to determine when start imaging or when to end.



I would really like this idea. This is what I used for other programs and find it useful.

I, too, have a complex horizon at home and would love to see this feature.


I was just dealing with this same issue. The skyX horizon file is just a text file that you can probably be incorporate easily. I think the better recommendation is to come up with a standard format for Voyager to consume. Users would work with their favorite tool and convert it as needed. In the interim, I was contemplating use of the hour angle and altitude constraints as a way to do it in my situation as my blocking trees are all located from 270-360.

I would also be quite happy about this feature. In my opinion this would also be great to have as a per profile option similar to “Not Allow Goto to Altitude lower than Degrees” in the Mount settings.

I also strongly support this feature request and had already planned to ask for local horizon support when I found this forum entry. For my location it is the most important planning aspect and therefore would highly increase the value of Voyager Advanced.