WCPS-Manual / fieldExpr
The fieldExpr element specifies a unary induced field selection operation. Fields are selected by their name, in accordance with the WCS range field subsetting operation.
NOTE Due to the current restriction to atomic range fields, the result of a field selection has atomic values too.
C1 be a coverageExpr
comp be a fieldName which is a range field of type t within rangeType(C1).
Let C be a coverage with range type integer. Then the following request snippet describes a single-field, integer-type coverage where each cell value contains the difference between red and green band:
C.red - C.green