Convert a mask or Dsurface with an irregular outline into a mask or Dsurface with a rectangular outline and the same bounding box. This enables contour plotting.
object of class mask or Dsurface
The covariates of new points are set to missing. The operation may be
reversed (nearly) with
subset(rectmask, attr(rectmask, "OK")).
The results are unpredictable if the mask has been rotated.
A rectangular mask or Dsurface with the same ‘area’, ‘boundingbox’,
‘meanSD’, ‘polygon’ and ‘polygon.habitat’ attributes as
logical vector attribute ‘OK’ is added identifying the points
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