alias mars.origin = centre;

meta    forecastperiod    g1fcperiod(P1,P2,timeRangeIndicator,indicatorOfUnitOfTimeRange) : no_copy;
alias   mars.fcperiod = forecastperiod;
unalias mars.step;

alias   mars.refdate = referenceDate;
unalias mars.date;
alias mars.method = methodNumber;
if (class is "od") { alias mars.system = systemNumber; }