"BAD WCS" error is too verbose

[pllim]

Between

ginga/ginga/util/wcs.py

Lines 68 to 69 in c847163

	assert (ra >= 0.0), WCSError("RA (%f) is negative" % (ra))
	assert ra < 360.0, WCSError("RA (%f) > 360.0" % (ra))

and

ginga/ginga/AstroImage.py

Lines 811 to 821 in c847163

	self.logger.warning("Bad coordinate conversion: %s" % (
	str(e)))
	ra_txt = dec_txt = 'BAD WCS'
	try:
	# log traceback, if possible
	(type_, value_, tb) = sys.exc_info()
	tb_str = "".join(traceback.format_tb(tb))
	self.logger.error("Traceback:\n%s" % (tb_str))
	except Exception:
	tb_str = "Traceback information unavailable."
	self.logger.error(tb_str)

I keep seeing traceback info on screen when WCS cannot be computed. This is too verbose to my liking since I see "BAD WCS" on the viewer anyway. I think the code can be refactored to only output traceback when log level is set to debug. However, I cannot find a easy way to do this without refactoring both wcs.py and AstroImage.py. Any thoughts, @ejeschke ?

[ejeschke]

I think that WCS errors are kind of in a special category. There are times when you don't care about the WCS and then almost any error messages seem annoying, but when you absolutely care about the WCS you definitely need informative error messages, possibly with a full stack trace (e.g. trying to debug some issue in gwcs).

[ejeschke]

Maybe we could handle it via a preference/setting? For the info_xy stuff, it could be turned off, but if we need to debug something we need to be able describe an easy way to turn it on.

[ejeschke]

I've never been happy with that info_xy stuff being in AstroImage anyway. Might be a good opportunity to rethink/redo how that is handled.

[pllim]

Well, we have loglevel, so if it emits under DEBUG, then to enable it for debugging, we can pass in --loglevel=10, otherwise it is silenced? I would prefer to get rid of try ... except ... too, as except is expensive when it happens. Maybe there is a way to catch this with if ... else ... instead?