@BeginModule
@NewPage
@Name      = Maskbox
@Title     = Mask a box
@Section   = Modification
@Class     = Modification
@Arguments = ifile ofile
@Operators = masklonlatbox maskindexbox

@BeginDescription
Masks a box of the rectangular understood field. The elements inside 
the box are untouched, the elements outside are set to missing value.
All input fields need to have the same horizontal grid.
Use @mod{sellonlatbox} or @mod{selindexbox} if only the data inside the
box are needed.
@EndDescription
@EndModule


@BeginOperator_masklonlatbox
@Title     = Mask a longitude/latitude box
@Parameter = lon1 lon2 lat1 lat2

@BeginDescription
Masks a longitude/latitude box. The user has to give the 
longitudes and latitudes of the edges of the box.
@EndDescription
@EndOperator


@BeginOperator_maskindexbox
@Title     = Mask an index box
@Parameter = idx1 idx2 idy1 idy2

@BeginDescription
Masks an index box. The user has to give the indexes of the 
edges of the box. The index of the left edge can be greater 
then the one of the right edge.
@EndDescription
@EndOperator


@BeginParameter idx1
@Item = lon1
FLOAT    Western longitude
@Item = lon2
FLOAT    Eastern longitude
@Item = lat1
FLOAT    Southern or northern latitude
@Item = lat2
FLOAT    Northern or southern latitude
@Item = idx1
INTEGER  Index of first longitude
@Item = idx2
INTEGER  Index of last longitude
@Item = idy1
INTEGER  Index of first latitude
@Item = idy2
INTEGER  Index of last latitude
@EndParameter


@BeginExample
To mask the region with the longitudes from 120E to 90W and
latitudes from 20N to 20S on all input fields use:
@BeginVerbatim
   cdo masklonlatbox,120,-90,20,-20 ifile ofile
@EndVerbatim
If the input dataset has fields on a Gaussian N16 grid, the same box can
be masked with @oper{maskindexbox} by:
@BeginVerbatim
   cdo maskindexbox,23,48,13,20 ifile ofile
@EndVerbatim
@EndExample
