How to keep horizon from moving so I can watch sunrise?

[tinmanic]

I'm using Celestia 1.6.0, and I want to stand in a single spot on Earth and watch the sunrise/sunset. But when I go to a spot and look at the horizon, over time the horizon tilts to the side and eventually does a complete 360 to the point where I can't even see the ground anymore. How do I do this without the ground moving?

What I've been doing is choosing a city and then pressing CTRL-G to go the surface. In other words, I hit <enter>, type "Earth/Paris", <enter>, and then CTRL-G.

The educational version (1.5.1-ED) has a pre-set module where you're standing in a spot in March 2005 and can watch the sunset without the ground shifting, so I know it's possible, but I can't figure out how to do it.

Thanks!

[selden]

Typing a Ctrl-G (goto surface) followed by a Ctrl-F (make arrow keys alt-azimuth) should work under Windows. After doing that and turning the time rate way up, the horizon stayed horizontal for me.

[selden]

Aha!
The horizon stays stable if I place the viewpoint directly above the destination and then use Ctrl-G. Approaching the destination at an angle is what causes problems.

In other words:

Right-mouse-button-click on the Earth.
In the popup menu select Mark.
Rotate the Earth (e.g. by holding down the right-mouse-button and moving the mouse) until the mark is centered on the desired destination.
then type Ctrl-G

Does this help?

[tinmanic]

Yes, this seems to work. Thanks!

[BobHegwood]

I learned something from this exchange too.
As always, thanks very much for your never-ending help Selden.

[selden]

I think the problem with the horizon might be caused by the viewpoint being relative to the location Paris and not relative to the object Earth. My guess is that locations don't have any orientation information associated with them, so Celestia can't make the viewpoint stay horizontal. When I goto Paris then click on (select) Earth and type a Ctrl-G, after the Ctrl-G operation finishes, the horizon stays horizontal as time passes.

[chris]

I think the problem with the horizon might be caused by the viewpoint being relative to the location Paris and not relative to the object Earth. My guess is that locations don't have any orientation information associated with them, so Celestia can't make the viewpoint stay horizontal. When I goto Paris then click on (select) Earth and type a Ctrl-G, after the Ctrl-G operation finishes, the horizon stays horizontal as time passes.

This is pretty close to correct... The actual problem is with the way a body fixed frame is defined for locations. It should have the same axes as the body-fixed frame of the location's parent body. Currently, it does not. I've got a patch to fix the problem, but it could cause problems with a small number of cel URLs, specifically those defined with a body-fixed frame (i.e. 'sync orbit') centered on a location object.

--Chris

[tinmanic]

Thanks for the response, Chris.

[chris]

Thanks for the response, Chris.

You're welcome! I just committed a fix for this problem to SVN (revision 4851)

--Chris

[tinmanic]

I just committed a fix for this problem to SVN (revision 4851)

Forgive me but what does that mean exactly?

[selden]

I just committed a fix for this problem to SVN (revision 4851)

Forgive me but what does that mean exactly?

It means that if you have configured your system so you can compile Celestia from scratch, you can download the fixed software from SourceForge and create a copy of Celestia which does not have the problem.

Building Celestia from scratch is relatively easy under Windows if you install Tortoise SVN, Visual C++ 2008.Express Edition and the Windows SDK. All are free. See http://en.wikibooks.org/wiki/Celestia/D ... 2_platform for instructions.

Note: VS2008 and the SDK are very large.

[tinmanic]

Thanks!