’s value can only be set once (for instance as an option when the Moc constructor is invoked). An error will be reported if a subsequent attempt to set or clear the attribute is made. If no value is supplied for MaxOrder before the first area of sky is added to the empty Moc, then a default value will be selected and set, depending on the method used to add the first area to the Moc:
AST_ADDCELL: the order of the specified cell.
AST_ADDREGION: if the added Region is a Moc, then the Moc
’ s MaxOrder value is used, Otherwise
the value used corresponds to the resolution closest to 0.1% of the linear size of the Region being
added (determined using method AST_GETREGIONDISC).
AST_ADDPIXELMASKX: the smallest order that results in the cells in the Moc being no larger than the size of the pixels in the centre of the pixel mask.
AST_ADDMOCDATA: the largest order present in the supplied normalised MOC data array.
AST_ADDMOCString: the largest order present in the supplied MOC.
A default value of -1 will be returned for the MaxOrder attribute prior to its value being set.
The MaxRes attribute is equivalent to MaxOrder but expresses the resolution as a number of arc-seconds rather than as a HEALPix order.
Increasing the HEALPix order by one roughly halves the resolution of the Moc. For instance, a value of 18 corresponds to a resolution of about 0.8 arc-second, and 19 corresponds to about 0.4 arc-seconds.