Some quick previews... [Large graphics inside]

fsgregs · Post #121by **fsgregs** » 10.10.2006, 21:56

Will the changes in 1.5.0 affect url's for all objects, or just for the Sun? For example, if a cel:url identifies a spacecraft in orbit position around Earth (Sol/Earth), will that url no longer go to that spacecraft in 1.5.0?

God ... I hope not! That would be a DISASTER!!!

Frank :cry:

Post #122by **selden** » 10.10.2006, 22:14

Frank,

Currently all URLs are incompatible. As I mentioned, Chris is hoping to implement a backward compatibility, but that hasn't happened yet.

Chuft-Captain · Post #123by **Chuft-Captain** » 11.10.2006, 01:54

selden wrote:Frank,

Currently all URLs are incompatible. As I mentioned, Chris is hoping to implement a backward compatibility, but that hasn't happened yet.

IMHO, 1.5 URL's will have to have some sort of "tag" or distinguishing feature which will allow the program to distinguish between them and the pre-1.5 URL's. The program would then be able to apply a correction vector to the old ones.
(Of course, this is much easier to say, than to do :wink:

)

fsgregs · Post #124by **fsgregs** » 11.10.2006, 23:43

Good Grief!

If 1.5.0 invalidates the positioning of all cel:urls, that is .... well .... HORRIBLE NEWS!!!!!! The educational activities have close to 400 cel:urls alone. Some of them took me 20 minutes to get just right, with the perfect angle of view, time frame, speed, etc.

PLEASE DO NOT TELL ME THEY WILL NO LONGER BE VALID!!!!!!! :evil:

Other add-ons using cel:urls abound in the Celestia add-on database. Please - Chris ... figure out how to retain the validity of all of this work!!! :cry:

Frank

Malenfant · Post #125by **Malenfant** » 12.10.2006, 00:26

I'm hoping that Chris will provide a way to convert between the old URLs and the new ones. Or maybe use something in the cfg file that will allow people to specify what origin they want to use when they turn on Celestia.

It may also be possible to have a special version of Celestia 1.5.0 that doesn't have the updated origin, and then you can package that with your scripts.

However, if you're arguing that we should maintain an scientifically inaccurate, arbitrarily defined fudge for the origin of Celestia's co-ordinate system just so that script writers can avoid the hassle of changing their Cel URLs, then I'm afraid you're not going to get much sympathy from me. Yes, sometimes changes are required that will screw a lot of people up, but I think it's better to bite the bullet and accept the change if it will allow other benefits (e.g. with the solar system barycentre is the origin, other useful features will be possible using that). Otherwise the same old errors are going to be propagating in future versions of the program, that really should have been fixed sooner.

Either way though, hopefully there will be a way to deal with this without making your life too difficult.

Post #126by **ElChristou** » 12.10.2006, 00:39

I agree with Mal, better fix things right now than write hundreds of new wrong URLs...

Paolo · Post #127by **Paolo** » 12.10.2006, 10:14

fsgregs wrote:Good Grief! If 1.5.0 invalidates the positioning of all cel:urls, that is .... well .... HORRIBLE NEWS!!!!!! The educational activities have close to 400 cel:urls alone. Some of them took me 20 minutes to get just right, with the perfect angle of view, time frame, speed, etc.

PLEASE DO NOT TELL ME THEY WILL NO LONGER BE VALID!!!!!!!

Other add-ons using cel:urls abound in the Celestia add-on database. Please - Chris ... figure out how to retain the validity of all of this work!!!

Frank

I continue to say that there is more than one argument to justify a compatibility brakedown in the data formats for the next major release of Celestia (1.5.0 -> 2.0.0?). In any case I belive that it is possible to write a simple converter for the cel-urls.

Kind regards

buggs_moran · Post #128by **buggs_moran** » 12.10.2006, 15:36

fsgregs wrote:Good Grief! If 1.5.0 invalidates the positioning of all cel:urls, that is .... well .... HORRIBLE NEWS!!!!!! The educational activities have close to 400 cel:urls alone. Some of them took me 20 minutes to get just right, with the perfect angle of view, time frame, speed, etc.

PLEASE DO NOT TELL ME THEY WILL NO LONGER BE VALID!!!!!!!

Other add-ons using cel:urls abound in the Celestia add-on database. Please - Chris ... figure out how to retain the validity of all of this work!!!

Frank

If it comes down to doing this one by one, I would be happy to help fix them Frank.

Post #129by **chris** » 12.10.2006, 15:45

fsgregs wrote:Good Grief! If 1.5.0 invalidates the positioning of all cel:urls, that is .... well .... HORRIBLE NEWS!!!!!! The educational activities have close to 400 cel:urls alone. Some of them took me 20 minutes to get just right, with the perfect angle of view, time frame, speed, etc.

PLEASE DO NOT TELL ME THEY WILL NO LONGER BE VALID!!!!!!!

Other add-ons using cel:urls abound in the Celestia add-on database. Please - Chris ... figure out how to retain the validity of all of this work!!!

Frank

I will attempt to make old cel: URLs work in Celestia 1.5.0, but I'm afraid that I can't guarantee that I'll come up with a scheme that works. The problem is a bit tricky. I'd initially thought that I could just apply a scale and translation factor to older cel: URLs, but that's not what needs to be done. The correction actually depends on what star is near the location in the cel: URL, because the bug was in the conversion from universal to astrocentric coordinates. In fact, I'm fairly certain that there's no way to correct cel: URLs that will work 100% of the time, but it may be good enough to fix 99.9% of the cel: URLs out there.

--Chris

rthorvald · Post #130by **rthorvald** » 12.10.2006, 20:47

buggs_moran wrote:
fsgregs wrote:that is .... well .... HORRIBLE NEWS!
If it comes down to doing this one by one, I would be happy to help fix them Frank.

This task isn??t as enormous as it appears on the surface, though it will be tiresome enough: remember that if you select an "old" CelUrl after the 1.5 correction, you will come out at the wrong place, but still at the correct time, with the relevant object still selected. So, it is only a GoTo and reorientation that will be neccecary for each case.

- rthorvald

fsgregs · Post #131by **fsgregs** » 12.10.2006, 21:06

Thanks everyone for the offers of assistance in converting the cel:urls. I may take you up on it.

If Chris's planned fix can correct 90% of the old cel:urls, that would be great.

f you select an "old" CelUrl after the 1.5 correction, you will come out at the wrong place, but still at the correct time, with the relevant object still selected. So, it is only a GoTo and reorientation that will be neccecary for each case.

If this is true in all cases, then it will still be a time consuming fix (400 cel:urls is a LOT of places to fix), but I'd agree that the time to correct it will take less.

Here's hoping a simple solution becomes possible.

Thanks again folks

Frank

rthorvald · Post #132by **rthorvald** » 11.11.2006, 19:49

... Just in case you wondered what it would be like to live in a big cave in space. Where the horizon bends the wrong way...

(still in progress: the landscape is lacking a number of features here.
Btw, what you see down in the right corner is a city with several scyscrapers. It is a big cave.

- rthorvald

Post #133by **t00fri** » 11.11.2006, 20:02

This makes me suggest to think about a city located in Anti-DeSitter space ;-)

Bye Fridger

Cham · Post #134by **Cham** » 11.11.2006, 20:06

t00fri wrote:This makes me suggest to think about a city located in Anti-DeSitter space

LOL !

rthorvald · Post #135by **rthorvald** » 11.11.2006, 20:09

t00fri wrote:This makes me suggest to think about a city located in Anti-DeSitter space

That??s way too abstract for me. I looked it up, and didn??t understand much. How about a short explanation in layman??s english...?

- rthorvald

Cham · Post #136by **Cham** » 11.11.2006, 20:20

Anti-deSitter spacetime (AdS for short) is a solution of Einstein equation in vacuo, with a negative cosmological constant. The metric of spacetime is then (in some spherical coordinates system) :

Here, Lambda is the (negative) cosmological constant. In pure "classic" empty space, this constant is zero. Here, "c" is light speed, "t" is time, "r" is a radius coordinate.

This metric describes the geometry of the AdS spacetime. It tells how particles should move, how light rays bends, etc.

There are some strong speculations in the physics community about its physical signifiance for our universe, and maybe other universes "out there".

Post #137by **t00fri** » 11.11.2006, 20:25

rthorvald wrote:
t00fri wrote:This makes me suggest to think about a city located in Anti-DeSitter space

That??s way too abstract for me. I looked it up, and didn??t understand much. How about a short explanation in layman??s english...?

- rthorvald

Well, I am afraid I can't manage to explain Anti-De Sitter space-time in more popular terms than e.g. the respective Wiki does.

http://en.wikipedia.org/wiki/Anti_de_Sitter_space

Clearly, I think this should be another challenge for Chris to implement a local respective frame for Celestia. ;-)

As Cham obviously was aware of above , Anti De Sitter space-time has important applications in a general relativity context and in cosmology.

Bye Fridger

rthorvald · Post #138by **rthorvald** » 11.11.2006, 20:29

Ok, thanks, both. New concept for me. I see i have some reading to do :-)

- rthorvald

Post #139by **t00fri** » 11.11.2006, 20:40

rthorvald wrote:Ok, thanks, both. New concept for me. I see i have some reading to do

- rthorvald

Joking aside.

5d Anti-De Sitter space has become tremendously popular since ~5 years, due to what we call a particular "Duality" between two entirely different theories, each with great relevance in theoretical physics:

A duality between two theories typically concerns the statement that these are describing the SAME physics, despite looking dramatically different!

It was Maldacena who pointed out that a theory like Quantum Chromodynamics in (3+1) dims (describing the Stong Interactions) and Einstein's Gravitation in a 5 dim Anti-De Sitter Space are describing the SAME physics! Typically such Dualities refer to weak and strong interactions, respectively.

That statement opened dramatic perspectives...obviously. The respective duality runs under the name "ADS-CFT" correspondence.

Bye Fridger

rthorvald · Post #140by **rthorvald** » 18.11.2006, 20:15

Regarding the cave - this is an illustration of scale:

- rthorvald