TelescopeControl: Incorrect epoch for Celestron scopes

[Peter Mousley]

(This is the same as I reported on SF mailing list 15 Jun 10, but there hasn't been any feedback.)

I have a Celestron CPC scope and have always noticed the scope's displayed coordinates in Stellarium do not quite match the actual coordinates. A lot of the time this doesn't matter, but at higher powers the target can be outside the FoV. I modified the code with the assumption that it may be an epoch/equinox issue and, sure enough, I now get very accurate alignment. Doing some research, it seems the latest 4.18 hand-controller firmware (which I use) changed from J2000 to equinox of date/JNow processing (http://www.nexstarsite.com/Firmware/CPCFirmware.htm).

Two possible, but partial, patches (opt1 and opt2) intended for initial testing and feedback will follow. Both patches call the j200ToEquinoxEqu and equinoxEquToJ2000 functions when required. But opt1 adds an extra parameter (pointer to StelNavigator) to functions where this is required, but that means changes to the parent and sibling classes. Opt2 is simpler and acquires it's own pointer when required.

Ultimately it would be more useful to have a general solution that can work with all scopes. However, for this to work properly, other functions would be required (reading of firmware version, etc.). If someone could confirm that either patch works properly I'll look at adding the other required extensions. Or, let me know if you have a better/more preferred way for this to be implemented. (To me, neither patch is very good as there is too much code dependence - scope interface code should not need knowledge of the main app and other core components just to convert coord systems. Perhaps there should be a library, updated by StelNavigator for example, that provides these types of functions?)

Peter

[Bogdan Marinov (daggerstab)]

I implemented a manual override: now the user can choose which coordinate system to use in the Telescope Configuration window.

The fix has been committed as revision 4813 of the trunk branch in Stellarium's Bazaar repository at Launchpad:
http://bazaar.launchpad.net/~stellarium/stellarium/trunk/revision/4813