Method for extracting 'x values' from an object of class fromXYZ
# S3 method for fromXYZ
xvals(obj, ...)
a spatialAtRisk object
additional arguments
the x values
xvals, yvals, zvals, xvals.default, yvals.default, zvals.default, yvals.fromXYZ, zvals.fromXYZ, xvals.SpatialGridDataFrame, yvals.SpatialGridDataFrame, zvals.SpatialGridDataFrame