Millisecond Pulsars freeze

Telepath · Post #1by **Telepath** » 01.06.2006, 20:07

I have noticed a strange thing happening with millisecond pulsars in Celestia.
PSR 1257+12 for example.

If I slow down time to better observe the rotation rate, when I get to 1000x (slower), it appears to freeze completely.

(Best way to observe this is to press CTRL-W and orient the star to view one of the poles.)

Anyone else experienced this?

Celestia 1.4.1

Telepath · Post #2by **Telepath** » 04.06.2006, 12:46

C'mon people,

You seem to have plenty of time to discuss why there's little feedback: http://celestiaproject.net/forum/viewtopic.php?t=9637

...so why not take 30seconds to provide some feedback on this post.

I've given exact instructions on how to reproduce it.
Is it a bug or not?

I personally don't care whether this gets fixed or not, but I would think it's in your interests to provide some acknowledgment if you wish people to continue to make the effort to report bugs.

Post #3by **ElChristou** » 04.06.2006, 14:03

at -10000x, it don't freeze for me, but it's so slow that you must wait a few seconds to see a spot moving a few px...

Malenfant · Post #4by **Malenfant** » 04.06.2006, 14:38

I don't even see anything flashing at all when I look at it in Celestia 1.4.1. Is there some kind of add-on you need to view this?

ajtribick · Post #5by **ajtribick** » 04.06.2006, 14:46

I came across this issue a while ago. I'm almost certain I posted a thread about this and got some kind of response, but the searches I've done turned up nothing.

Post #6by **dirkpitt** » 04.06.2006, 16:09

Telepath wrote:I have noticed a strange thing happening with millisecond pulsars in Celestia.
PSR 1257+12 for example.

If I slow down time to better observe the rotation rate, when I get to 1000x (slower), it appears to freeze completely.

I cannot reproduce this issue with both 1.4.1 and the latest CVS build so it looks like an issue with your config.
Please report hardware and operating system configs along with bug reports.

Post #7by **selden** » 04.06.2006, 16:46

I think I see the same effect that Telepath sees.

When looking at the north pole of PSR1257+12

When Celestia's time rate is set to 100x slower, the star rotates at about 2Hz.

When Celestia's time rate is set to 1000x slower, the star does not rotate continuously. Instead, it rotates in varying steps of irregular sizes at irregular intervals. Usually there are several minutes between steps. I have the impression that it rotates faster if the disk is being accessed frequently by some other program. (It suddenly started turning faster while the SMART test program on my system was doing a disk scan.)

System:
1GB 3.4GHz P4-550, WinXP Pro SP2
128MB GF 6600 GT, ForceWare v84.21
Celestia built from CVS, Visual Studio Academic 2003

p.s. this is not a new bug. I seem to remember seeing this reported a long time ago.

Malenfant · Post #8by **Malenfant** » 04.06.2006, 17:32

Oh I see now, it's not flashing, it's that you're looking at the starspots moving on the surface. Yeah, at 1000x slower the spots jerk slowly around the star. I think there's a 'strobe effect' going on here where the spots appear to move only when a time increment is synchronised with them.

But I can still see the spots moving at 1000x slower. It doesn't seem to move at 10,000x slower though.

Post #9by **ElChristou** » 04.06.2006, 17:43

selden wrote:When Celestia's time rate is set to 1000x slower, the star does not rotate continuously. Instead, it rotates in varying steps of irregular sizes at irregular intervals. Usually there are several minutes between steps. I have the impression that it rotates faster if the disk is being accessed frequently by some other program. (It suddenly started turning faster while the SMART test program on my system was doing a disk scan.)

Yep, I get also this behavior but at -10000x; effectively, if I run another app, it turns a bit faster... really strange...

Fightspit · Post #10by **Fightspit** » 05.06.2006, 16:44

Morever, after to put at +10000000000x !!!!, and return to real time or more slowly, the pulsar stop his rotation ...
Very strange :!:

rra · Post #11by **rra** » 06.06.2006, 20:36

If I drag and keep moving another window partly over the Celestia window , the stars seems to rotate smoothly, if I stop the dragging of the other window over celestia the rotatian stops immediately.
Seems to me an (windows) sync problem, it is familar with Excel manually selecting an area faster when moving the mouse-cursor around.

Does this also occur on Linux systems ??

Ren?©

p.s. I have celestia 1.4.1. running on windows XP-SP2

fsgregs · Post #12by **fsgregs** » 13.06.2006, 00:04

I have seen this effect repeatedly with spacecraft for over a year now. If I track a spacecraft using the [T] key, they will fly by at real speed. They will pass by slower at -10x slower and -100x slower. However, at -1000xslower, they stop completely, even if they should still be moving slowly.

It seemed to first appear in Celestiua 1.4.0. Celestia 1.3.2 never had the problem, even when using the same models and time scales. At -1000x, the spacecraft would pass me slowly.

I have always assumed it was a bug in 1.4.0 that continues in 1.4.1! I just try to work around it.

Frank

Post #13by **chris** » 27.06.2006, 06:03

Much to my surprise, this problem turns out to be a precision limitation of double precision floating point arithmetic. The faster your frame rate, the smaller the per frame time increment, and the more susceptible it is to being treated as effectively zero. I'm not sure what was happening in earlier versions that kept the problem from appearing. There's no simple fix for the problem now.

--Chris

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