# Angle Measure: angle to the horizon

Bug #1208143 reported by Solarstar on 2013-08-04
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Fix Released
Wishlist

### Bug Description

I have an idea for the extention : Angle Measure

It would be very helpful to me if the tool would show the angle of inclination to the horizon.
I find objects in the sky which are very low visible with a technique called starhopping. That means I orientate myself on bright stars and try to define a distance and angle relativ to the object that I am looking for.
So far I am only guessing angles, so it would be great if Stellarium could also show me a number.
It is especially important to me because I look through a dubsonian telescope which shows stars horizontal and vertical upside down ! :)

I have seen a tool that can do this in the program GIMP that many are sure familiar with. I made a quick screenshot to visualize what I mean:

http://s9.postimg.org/tt87l2ljj/Neigungswickel.png

In additon I noticed that i can not pan the horizon anymore when the angle measurement tool is active. Therefore I suggest that this tool becomes active while you hold down shift-key + draw a line with LBM.

Also from the Tool Observability Analysis I know it is possible to define a color for the text on screen with sliders. Maybe consider adding for Angle Measurement too since the code is already written or even combine the two for a more uniform interface. It's up to you :)

Best wishes
Solar

Thank you to introducing me to launchpad Alexander Wolf ( on IRC )

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## Related branches

 Solarstar (eternal-lands-solarstar) wrote on 2013-08-04: #1
 Changed in stellarium: importance: Undecided → Wishlist
 Ariane Stevens (sjstar) wrote on 2014-01-23: #2

Just a point. I think this person means position angle - the angle north through east, where 0 deg is north.

It is simply calculated by PA = tan^-1 x (15 x Delta RA x cos Dec. / Delta Dec.)

With Delta RA in seconds (NOT arcsec), Dec= in arcsec

For separations larger than 2 degrees, the precision likely decreases.

Also you would also have to take precession into account.

 Alexander Wolf (alexwolf) wrote on 2014-02-16: #3

A fix has been committed as revision 6579 of the trunk branch in Stellarium's Bazaar repository at Launchpad:

 Changed in stellarium: milestone: none → 0.13.0 assignee: nobody → Alexander Wolf (alexwolf) status: New → Fix Committed
 summary: - feature request for Angle Measurement+ Angle Measure: angle to the horizon
 Bogdan Marinov (daggerstab) wrote on 2014-02-25: #4

I think that there might be some confusion here. Position angle is defined in relation to the geocentric equatorial coordinate system:
http://en.wikipedia.org/wiki/Position_angle

What the user requested is "angle of inclination to the horizon", which is not the same, especially given the mention of a Dobsonian telescope. Dobsonian mounts are altitude/azimuth mounts. Which makes the request somewhat unclear - if the user wants the angle between an object and the horizon, that's the "altitude" displayed in the left-upper corner box when the object is selected. For starhopping with an alt/az mount, one can get the necessary angle for each axis separately - by calculating the difference between the altitudes (or the azimuths) of the two objects.

So I'm not sure if that code is a fix for this particular feature request.

 Changed in stellarium: status: Fix Committed → In Progress
 Alexander Wolf (alexwolf) wrote on 2014-02-26: #5

Thanks for comment Bogdan! I think I should wait comment from request starter.

 Solarstar (eternal-lands-solarstar) wrote on 2014-03-05: #6

I read your comments. It's more then half a year ago since i suggested this, but nice to see that at some people are showing interst. At the moment i'm a bit short in time hence my short replay. I will soon elaborate on my idea, perhaps with some graphics if needed.

Solar *

 Changed in stellarium: milestone: 0.13.0 → 0.13.1
 Changed in stellarium: milestone: 0.13.1 → none
 Changed in stellarium: assignee: Alexander Wolf (alexwolf) → gzotti (georg-zotti) milestone: none → 0.13.1
 Changed in stellarium: milestone: 0.13.1 → 0.13.2
 Alexander Wolf (alexwolf) wrote on 2014-10-11: #7

A fix has been committed as revision 7072 of the trunk branch in Stellarium's Bazaar repository at Launchpad: http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/7072

 Changed in stellarium: milestone: 0.13.2 → 0.13.1 status: In Progress → Fix Committed
 Changed in stellarium: status: Fix Committed → Fix Released
 Solarstar (eternal-lands-solarstar) wrote on 2014-10-19: #8

Today I got a chance to test the new plugin ! Great work everyone !

After installing I checked the box 'Load on startup'. I try to click for more configuration but there was nothing. After the new start I was able to draw a line over the horizon. And not only that, it's curved ! :D I didn't ask for it, but I like that idea.
Then later I found out that there are indeed more configurations possible. My mistake was that i didn't know it has to be loaded at least once to open. The distance over the virtuel horizon is given in degr. min. sec. That's good.

Anyway, I clicked on 'Display with position able' and well , I almost found what i asked for ;)
Here is what happens: It gives the number of degrees around the origin (where i clicked first time) between 0 and 360°, where zero degr. is pointing to the zenit. The Display information is in the same line (PA= DD° MM' SS.SS")

Now I suggest two changes.

Add a line break behind the distance. Delete the the brackets '( )' and 'PA=' .

For humans it is easy to imagine a horzon. For example, you want to anchor a picture frame to a wall. Many people can very well tell if the frame is horizontal or not. Same principle for star hopping. Take one star and imagine a virtuel horizon. You can find another star by knowing its distance and the degr. against the horizon. Onother way would be to know the delta X and delta Y but I find that less practical because you have to remember the relation between the X and Y distance and the distance itself. Human brains are very good at evaluating shapes and patterns. So distance and degree will be better.

Let the degrees be numbers between 0° and 90° when above the origin and 0° to -90° when below the object. Smaller numbers are easier to handle. It's more intuitive and less technical.

Ok let's asume you look up a star you find in the real sky, then find it in stellarium and you use the angle measurement tool for the information distance and angle. If you have a graduator on your teleskope, that would be good ( I don't have it yet). So most of the time I'm just guessing the numbers. Therefore I think degrees and minutes are enough info. Seconds is not neccessary, (plus the following digits). You are lucky enough if you guess the degr. right :)

I have two possible ways to pan the horizon. That's with the keys or (I prefer) with my left mouse. Now I can't do both, draw a line and pan. I suggest an option for an additional key to be hold down when drawing. For exanple Left-Shift-Key. The line can then remain active when you pan.

I hope I explain well and it's not too difficult to make the changes. I like to thank all devellopers involved. I will check soon again in case more question come up.

All the best
SolarStar

 Solarstar (eternal-lands-solarstar) wrote on 2014-10-19: #9

Edit: The checkbox name is Display with position angle'. And of course, the idea makes only sense for the Azimuthal grid (orange).

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