ctools

Since the RING background method is an iterative process, and the initial binning and background computation takes some time, it should be possible to specify an input sky map to ctskymap to apply different ring background parameters.

One option is to specify the input skymap directly to the inobs parameter. The tool should then be able to automatically detect whether the input file is a sky map, an event file or an observation definition file. The only related question is of whether the inobs parameter should be renamed, since a skymap is not formally an observation.

The other option is to add an inmap parameter, which by default is NONE. If this parameter is hidden, the default behavior of the tool would not change. I tend to favor this option, since the User interface is cleaner.