more sky, less landscape (horizon elevation)

[Alexander Wolf]

I hereby like to bring up an idea (feature request) which was originally requested here:

http://sourceforge.net/p/stellarium/discussion/278769/thread/f3ec2c36/

I know that there are not so many users who commented on it but until now all people were in favor of this idea. I really think it would be an improvement and an asset! Therefore, I think it's worth for developers to look into it...

Thanks
Trost

[Bogdan Marinov (daggerstab)]

This really needs a better description.

[Trost Looser (trostlooser)]

Sorry, I wasn't aware that feature requests are treated/entered as bugs! I am wondering why my last post isn't here...

Don't think of this feature as a different projection. Maybe following scenarios help understanding the desired view (see attached picture in original linked post):

Set the perspective to stereographic and put your horizon on the center of the screen being q straight line. Now imagine you are lifted several meters off the ground. Since the viewer is quite far away from the celestial sphere it will not affect the view of the stars really. The horizon panorama on the contrary will change significantly as the viewer is very close to it. The horizon panorama will apparently move down and parts of it leavning the user's field of view. No chqnge in projection here - still stereographic.

Another scenario: Put the projection again on stereographic and assume no movement of the camera (no tilting, shifting etc.). Now imagine you could enable a second screen above the original screen. More of the celestial dome would becomee visible as the image is not cut off at the top of the lower screen. The view would be continued in the other screen with all its projection properties and distortion applied. Now imagine that the landscape in the lower screen is now beeing "cropped". The whole (still) image can now be scrolled down with some of the additional image of the upper (second) screen beeing moved to the lower screen. The upper screen can now be turned off and the desired view in the lower screen is achieved.

Therefore, please do not regard this feature request as a new or different projection but rather as a cropping of the field of view! Looking at the mock-up image in the original sourceforge discussion post I really think that this kind of view is something many users are looking for and I believe that it would be a great feature and for developers worth looking into it...

Regards
Trost

[Alexander Wolf (alexwolf)]

*facepalm* Why you want add few spikes instead the usage mouse and zoom?

[Alexander Wolf (alexwolf)]

I'm repeating myself: if you really want this strange settings - just make it.

[gzotti (georg-zotti)]

There are (deprecated(?), unused) settings in config.ini which may be traces of earlier use of such a feature:

[video]
vertical_offset
horizontal_offset
viewport_effect

The offsets could be re-activated in OpenGL's default perspective projection with likely moderate effort. Not sure about the viewport in other projections though.
G.

[Bogdan Marinov (daggerstab)]

As far as I can remember, the offsets are remains of window positioning
code, and the viewport effect field served the spherical distortion and
fisheye projection features.

[Trost Looser (trostlooser)]

I didn't mean to insult any developer or disrespect anybody's work! I like Stallarium a lot and I think it is a great software! I am saying this since I am sensing a rather defensive and reluctant attitude here. All I want is to raise the suggestion of a new feature and I would regard it as a normal procedure to have the community comment on it and see if there is a majority which is in favor of this idea.

The attached picture by Alexander Wolf is NOT the desired view as described in the original post. His horizon is curved and does not reflect the view seen in reality. The goal obviously is to get more of the sky imagery and less of the horizon panorama using a flat horizon.

I can only point everybody's attention again to the attached mock-up image of the desired view (see link below) and ask if this is a desirable viewing option to be implemented in a future version of Stellarium. If agreed we might think about how to achieve this and get around the complications...

[Bogdan Marinov (daggerstab)]

The value of the FOV indicator in the bottom bar in your image (120 degrees) should hint to what exactly is the problem with that idea. Compare that value to the angular size of your screen as seen from your usual viewing distance. Or imagine what portion of the sky you would see if you saw it through a frame the size of your screen. Displaying a large portion of the 3D sky on a small plane surface inevitably introduces some kind of distortion. We can't change the size and aspect ratio of your screen.

If you want to visualize distortion, enable the azimuth grid (default key: Z). It's instructive to see what happens to it when you switch projections. If you want a perfectly flat horizon at all FOV angles, set your projection to "perspective". If you want to see the whole sky with little ground in the default stereographic projection, aim your view towards the zenith and zoom out. If you want to keep the view "square", switch to window mode and manipulate the window (or the settings in the configuration file) until it's square. In all projections, if the landscape distracts you, you can switch it off and use the horizon line instead.

As for "[It] does not reflect the view seen in reality": humans have binocular vision. Each eye has its own FOV, and they overlap only partially. Your brain integrates the two views into (the illusion of) a three-dimensional single view, editing out stuff like eye movement. By contrast, Stellarium simulates monocular vision, e.g. the sky as seen by a camera, a telescope or a pirate captain. The only way to approximate binocular vision with flat screens would be to have each eye see a different Stellarium screen, set to a slightly different, partially overlapping point-of-view. (I'm specifying flat screens because you can project Stellarium on a dome with a fish-eye or spherical mirror projector. In those cases, the curvature of the surface provides the same effect.)

About "I would regard it as a normal procedure to have the community comment on it and see if there is a majority which is in favor of this idea.":

First, it's really unclear if the idea is actually an idea (i.e. a feasible feature) and not a misunderstanding of some principles.

Second, "majority" in this situation is pretty much a meaningless phrase. It's not practically possible to conduct a representative survey of all Stellarium users, and even if it was, it would be impossible to know how much of them actually understood the question. ;) And since users normally outnumber greatly the developers, a "majority" is not hard to form, especially on a forum thread, where participation is self-selected. So the best we could say is that such-and-such feature is often requested. (Which is not necessarily the case with yours - we've had much more requests and complaints about time zone handling, for example. Guess on what I am supposed to be working right now instead of writing this.)

Third, the majority opinion is irrelevant: implementing a feature requires a developer who is both willing and capable to do it. Unless such person is found, no feature is going anywhere.

And finally, something about "If agreed _we_ might think about how to achieve this a...

[Alexander Wolf (alexwolf)]

Diff: http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/7746

[Trost Looser (trostlooser)]

Hey there,

I am very delighted to see that the improvement suggestion that I revived with this post was finally put into action! I tried the new offset feature and I am amazed by the effect of it and it makes me forget the rather rude conversation in this thread.
Personally, I am sure it is a fantastic new feature allowing everyone to see more of the sky and less of the landscape, exactly as desired. I therefore like to say a BIG THANK YOU to all the programmers who were working on this new feature and I hope that everyone can agree that it was worth the effort and that this feature was an asset to Stellarium.

Thanks again and kind regards

[gzotti (georg-zotti)]

Hi!

It was definitely worth the effort. Usually features are now implemented by those who critically need them themselves, that's the chance in open source ;-)
Unfortunately much of the discussion, but also the description, was a bit off. It's not about lifting off the ground or shifting panos around. The panos are now accurate if well done.

Kind regards,
Georg