## Using Default SkyFrame Attributes

The default values supplied for many SkyFrameSkyFrame attributes will depend on the value of the SkyFrame's SystemSystem attribute. In practice, this means that there is usually little need to specify many of these attributes explicitly unless you have some special requirement. This can be illustrated by using astShowastShow to examine a SkyFrame, as follows:

156#156

The output from this might look like the following:

157#157

Note that the defaults (indicated by the “`#`” comment character at the start of the line) for attributes such as the TitleTitle, axis Labels and Format specifiers are all set to values appropriate for the particular equatorial coordinate system that the SkyFrame represents.

This means, for example, that if we were to use this SkyFrame to format a right ascension value stored in radians using astFormatastFormat (§7.6), it would automatically result in a string in sexagesimal notation (such as “12:14:35.7”) suitable for display. If we changed the value of the SkyFrame's Digits attribute (which is inherited from the FrameFrame class), the number of digits appearing would also change accordingly.

These choices would be appropriate for a System value of “FK4-NO-E”, but if a different System value were set, the defaults would be correspondingly different. For example, ecliptic longitude is traditionally expressed in degrees, so setting “System=ecliptic” would result in coordinate values being formatted as degrees by default.

Of course, if you do not like any of these defaults, you may always over-ride them by setting explicit attribute values yourself.