Two free, open-source geometry calculators for astrophotographers planning or building an observatory — designed to give you real answers about whether your setup will physically work before anything gets bolted down or cut.
Setting up dome-sync in NINA requires knowing four signed numbers with the right sign conventions. Getting them wrong is easy and the feedback loop is slow — configure, run NINA, watch the dome miss, tweak, repeat, on a cold night with dew forming. The dome calculator grew out of that frustration.
The roll-off-roof calculator came from the same question in a different form. A roll-off roof is a genuinely different geometric problem from a dome, and the astrophotography software ecosystem has good dome-sync support but comparatively little for the equally real problem of whether your ROR's walls, parked roof, and floor let your assembly swing freely.
The dome calculator's core azimuth math is ported from NINA's DomeSynchronization.cs, using the same matrix conventions. Both tools are licensed under the Mozilla Public License 2.0 — the same license NINA uses — in recognition of that shared foundation.
These tools are not affiliated with, endorsed by, or supported by the NINA project or its developers.
Both calculators are fully client-side HTML — no server, no database, no data collection. The source is the page itself. Released under the MPL 2.0; contributions and forks welcome under those terms.
Astronomy fanatic. Hooked since childhood.
I can still remember the first time I saw Saturn's rings through a telescope. That was it — done. Space had me completely. As an adult I've been lucky enough to build my own observatory, and the hobby has given me so much over the years that I wanted to find a way to give something back. If these tools help even one person spend less time fighting their setup and more time under the stars, that's exactly what they were built for.
My astrophotography work — still very much a work in progress — lives here: M51_MyDestination on AstroBin →
Travellingbears & AndrewBares @ Cloudy Nights
For their inspiration, feedback, and generosity with their time. These tools are sharper, more useful, and more honest about what they're actually solving because of their input. Thank you.