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Physical simulation of the space engine

Posted: 10 Mar 2019 22:15
by Mr. Abner
ethos wrote:
Mr. Abner wrote:
ethos wrote:
Source of the post Is there a FOV that shows actual scale?

That depends on the size of your monitor and how far away your eyes are from it. Basic trigonometry.


It's 13.5 in tall and I'm about 25 in away from it.

Edit: Sorry, my mistake. After a quick flight in SE, it does indeed appear that the FoV is from top to bottom of the screen, not left to right. The formula below still works, but use the monitor height rather than the width. I have edited were appropriate.

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I believe S.E. displays FoV from side to side, so width of the monitor counts, not the height.

You have two right-angle triangles — from the center of your eyes to the middle of the monitor would be the "adjacent" side, from the center of the monitor to one of the side edges either the top or the bottom (or half the width height of your monitor) would be the "opposite" side.

Opposite over adjacent gives you the tangent of the angle between the "adjacent" side and the hypotenuse (which is from your eyes to the edge of the monitor).  So ((arctan of half the width height of the monitor divided by the distance from it) times two) will give the angle from your perspective from one side of the the top of the monitor to the other bottom. Set the FoV to that value, and your monitor should be the equivalent of an actual window into the SE universe.
:)

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So in your actual case, 13.5/2 = 6.75

6.75/25 = 0.27

arctan 0.27 = 15.1096

Times 2 = 30.2192 degrees.

I hope I haven't made an embarrassing error in my math. ;)

Physical simulation of the space engine

Posted: 11 Mar 2019 14:25
by ethos
[quote="Mr. Abner"][quote="ethos"][quote="Mr. Abner"]
That depends on the size of your monitor and how far away your eyes are from it. Basic trigonometry.[/quote]

It's 13.5 in tall and I'm about 25 in away from it.[/quote]
Edit: Sorry, my mistake. After a quick flight in SE, it does indeed appear that the FoV is from top to bottom of the screen, not left to right. The formula below still works, but use the monitor height rather than the width. I have edited were appropriate.

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[s]I believe S.E. displays FoV from side to side, so width of the monitor counts, not the height.[/s]

You have two right-angle triangles — from the center of your eyes to the middle of the monitor would be the "adjacent" side, from the center of the monitor to [s]one of the side edges[/s] either the top or the bottom (or half the [s]width[/s] height of your monitor) would be the "opposite" side.

Opposite over adjacent gives you the tangent of the angle between the "adjacent" side and the hypotenuse (which is from your eyes to the edge of the monitor).  So ((arctan of half the [s]width[/s] height of the monitor divided by the distance from it) times two) will give the angle from your perspective from [s]one side of the[/s] the top of the monitor to the [s]other[/s] bottom. Set the FoV to that value, and your monitor should be the equivalent of an actual window into the SE universe.
:)

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So in your actual case, 13.5/2 = 6.75

6.75/25 = 0.27

arctan 0.27 = 15.1096

Times 2 = 30.2192 degrees.

I hope I haven't made an embarrassing error in my math. ;)[/quote]


Do you need to convert from inches to cm first?

Physical simulation of the space engine

Posted: 11 Mar 2019 14:53
by Shaggy
[quote="ethos"]
Cool, thats much better. Is there a FOV that shows actual scale? Meaning if I was far enough away from Mercury in real life to appear a certain size to me, the Sun would be accurately be shown in size and scale as well?[/quote]

I think that would be FOV of 0. ;) That's because you can never have Mercury being closer to camera in same scale as sun being farther from camera unless you use ortographic view. As all the 3D games (with exception of some RTS or other top-down view games) SE uses perspective, not ortographic view.

Physical simulation of the space engine

Posted: 11 Mar 2019 15:27
by Mr. Abner
ethos wrote:
Source of the post Do you need to convert from inches to cm first?

Not at all. Trigonometry is really all about ratios. As long as the linear measurements are both in the same units, the ratio of the two will still be the same.

As for actual scale of Mercury and the Sun... if you mean as they look from Earth, then the FoV doesn't actually matter, just make sure you are about 1AU from the Sun. At that distance, the relative size of the Sun and Mercury will be as seen from Earth. You can then use the FoV as a zoom.

If you mean you want to see how big the Sun will look from Mercury, then set the FoV as described above, park yourself on Mercury, and break out the sunglasses. And cold drinks. And sunblock.

Physical simulation of the space engine

Posted: 14 Jan 2020 08:29
by longname
ethos wrote:
Is there something "off" with the scale of things? For example I'm trying to recreate the transit of Mercury as seen in this actual image.Image

however is SE, if I move away from Mercury far enough to make it appear as small as that in the image, the Sun is only slightly larger than Mercury is. Am i doing something wrong?

That picture was taken from Earth. Zoom into the Sun using Shift+LMB.

Physical simulation of the space engine

Posted: 03 Jul 2020 08:07
by Mosfet
longname wrote:
This forum is terrible at preventing spam.

It doesn't help a lot if you quote the post, don't you think?

Physical simulation of the space engine

Posted: 14 Jun 2021 10:32
by nbella91
I have a question regarding some of the features in SpaceEngine.  The gravitational lensing around black holes looks spectacular!  Is the effect solved using GR (specifically Schwarzschild Spacetime) or is it just a very good approximation?  I imagine it isn't a Kerr solution as the shape of lensing effect does not change if you change the spin of the black hole.  Any insight would be much appreciated!

Physical simulation of the space engine

Posted: 15 Jun 2021 15:29
by SpaceEngineer
It is a very good approximation based on general relativity solution :) More specifically, it is approximation of Schwarzschild black hole potential by Paczynski and Wiita (1980):

F = -G * M / (R - Rg)2

It is not a Kerr metric approximation, so spin is ignored. We still didn't find easy to implement (and fast to render!) Kerr solution. Probably it is way to complex for real-time graphics!

Physical simulation of the space engine

Posted: 15 Jun 2021 18:46
by nbella91
SpaceEngineer wrote:
It is a very good approximation based on general relativity solution :) More specifically, it is approximation of Schwarzschild black hole potential by Paczynski and Wiita (1980):

F = -G * M / (R - Rg)2

It is not a Kerr metric approximation, so spin is ignored. We still didn't find easy to implement (and fast to render!) Kerr solution. Probably it is way to complex for real-time graphics!

Thank you very much for the response!  A few of my professors (with whom I shared some video I captured in Space Engine) were curious if it was a full solution or approximation.  Admittedly, none of us thought of the Paczynski and Wiita potential!  We all agreed we have not seen such detailed and accurate lensing before that runs so smoothly in real time!  I agree that Kerr would be very difficult (if not impossible) but, hey, maybe one day our computers will be fast enough to handle it!  Keep up the excellent work!  I always recommend this software to all of my friends and colleagues (it's the best educational tool out there)!

Physical simulation of the space engine

Posted: 15 Jun 2021 21:24
by DoctorOfSpace
nbella91 wrote:
Source of the post I agree that Kerr would be very difficult (if not impossible)

This is something I have gone into quite a bit and tried figuring out with Duke but optimizing the Kerr metric requires assumptions for angles outside of equatorial and this gets very complex very fast, almost as complex as the metric itself.  That complexity adds to render time.  I still think there is a way to make some rudimentary form of it, but the Kerr metric is a nightmare.

Physical simulation of the space engine

Posted: 16 Jun 2021 00:27
by A-L-E-X
DoctorOfSpace wrote:
nbella91 wrote:
Source of the post I agree that Kerr would be very difficult (if not impossible)

This is something I have gone into quite a bit and tried figuring out with Duke but optimizing the Kerr metric requires assumptions for angles outside of equatorial and this gets very complex very fast, almost as complex as the metric itself.  That complexity adds to render time.  I still think there is a way to make some rudimentary form of it, but the Kerr metric is a nightmare.

Doc, I would love to see the famous Kerr Metric and ring singularities since it has been postulated that they may contain a wormhole into other universes (with two horizons, with the other universe inside the inner Cauchy horizon.)  Do you think something like this could ever be implemented in the program?

Physical simulation of the space engine

Posted: 16 Jun 2021 00:30
by A-L-E-X
SpaceEngineer wrote:
It is a very good approximation based on general relativity solution :) More specifically, it is approximation of Schwarzschild black hole potential by Paczynski and Wiita (1980):

F = -G * M / (R - Rg)2

It is not a Kerr metric approximation, so spin is ignored. We still didn't find easy to implement (and fast to render!) Kerr solution. Probably it is way to complex for real-time graphics!

would love to see ring singularities and an inner Cauchy horizon and perhaps even the conjectured pathway to another universe that may be part of the Kerr Metric!