i.rectify and masks

[IBH7CAB at MVS.OAC.UCLA.EDU]

A couple of questions:

1)  How is spatial interpolation peformed by i.rectify?  Cubic
    convolution?  Nearest neighbor resampling?

2)  How are GRASS users creating polygonal masks now that
    mapmask is not available in version 4.0?  I want to define
    circular-shaped catchments around sites and compare only
    the land use/land cover within these areas.

Any ideas would be greatly appreciated.

Cliff Behrens