Feature: Convex Hulls

[Integer-Ctrl]

"konvexe Hülle" ist ein mathematischer Algorithmus, der das kleinstmögliche Polygon berechnet, in dem alle Punkte einer beliebigen (verstreuten) Punktmenge enthalten sind.

• "convex hull" in library finden und anwenden (es gibt zwei Algorithmen, einer ist besser geeignet)
• Die CH soll automatisch
  • aus der Stick Figure
  • oder dem hochgeladenen Bild berechnet werden (ohne dass der User etwas tut)
• Es soll einen Button geben, mit dem das Polygon angezeigt werden kann,
• der User soll dann die Möglichkeit haben,
  • visuell weitere Sterne (mit einem "Picker Tool") anzuklicken, um sie hinzuzufügen
  • oder durch upload einer csv-Datei
• schreibe einen Sternkatalog von allen Sternen (HIP +Gaia), die in dem Sternbild sind (erstmal lokal speichern, soll ins neue repo und in die ASE). als Tabelle von "identifier | magnitude".

[janheinrichmerker]

Imported from https://git.uni-jena.de/fusion/teaching/project/2025sose/swep/sky-culture-maker/sky-culture-maker-app/-/issues/2

[janheinrichmerker]

There should be some code for this in the main Stellarium repo somewhere

[xLPMG]

"visuell weitere Sterne (mit einem "Picker Tool") anzuklicken, um sie hinzuzufügen" -> seems like this is written into "hull_extension" in the index.json

[RivinHD]

drawHulls(...) in ConstellationMgr.cpp Line 123
makeConvexHull() in Constellation.cpp Line 181

[Integer-Ctrl]

Hi @sushoff,
we discussed the ticket and have a few questions and observations:

1. Could you provide an example of how the convex hull is expected to be displayed in Stellarium? We explored the existing sky cultures but couldn’t find a way to enable or visualize convex hulls there.
2. We evaluated the effort required to compute the convex hull from an image and concluded that implementing this would not be feasible within a reasonable scope.
3. We also need an example CSV file from which the convex hull should be extended. Implementing this along with a picker interface seems to require very high effort compared to the expected benefit.

At the moment, we are not able to break down this ticket into actionable tasks. A clearer breakdown is necessary to identify what can realistically be implemented in the remaining time.

[sushoff]

Hi all,

oh, yes, you're right: displaying the hulls was not made easily visible in Stellarium. We decided that most users there won't need it (even more, as it is even scientifically new), see
Stellarium#4306

In Youla's SC-Maker, we had done it the following way:

1. when the user concludes drawing a stick figure, the convex hull is automatically computed. Most routines return a sorted list of vertices (coordinate tuples), and/ or even the size of the area.
2. The sorted list of vertices actually form a polygon that can easily be displayed (connect the sorted points with lines and from the last connect to the first).

My idea was: If that is easily doable with Georg's hull-routine, then you could simply include it.
Then, the user would need a button to switch on/ off the polygon.
(I believe, it will be more interesting during the making process of a SC then when it while using Stellarium as teacher)

This is what I consider to be done with (hopefully) almost no effort.

---

Then, all stars inside this area boundaries could be read from a star catalogue (this is what Georg's tool also does). The output would be CSV file currently. Of course, if you can adopt the solution above, this would also be easily possible - but I think, it would make sense to shift it to a next SWEP (as Heinrich suggested) because then, we could directly write it in a to-be-set up database instead of loose files floating around on local machines.

Furthermore, from the experiences in creating constellations, I know: when seeing the polygon the user might want to add points (stars) to the hull ... This would, probably, be yet another feature for a potential future SWEP.