Subsetting an icosahedral grid or data layers organized with them

This is a generic function used to access data from either a triangular or hexagonal grid using the names of the faces, integers or logical vectors.

The function extracts subsets of the gridlayer depending on different criteria.

Usage

subset

# S4 method for trigrid
subset(x, i)

# S4 method for hexagrid
subset(x, i)

# S4 method for trigrid,ANY,ANY
[(x, i)

# S4 method for gridlayer
subset(x, i)

Format

An object of class standardGeneric of length 1.

Arguments

x

(trigrid, hexagrid or facelayer) The object to be subsetted.

i

(logical, numeric or character) The subscript vector, specifying the faces that are used for subsetting. As in subset.

Value

Subset of the input grid. The class of the original object is retained, the @skeleton slot contains all previous information.

Details

The function returns subsets of the grid pertaining to the specified faces that can be used for additional operations (e.g. plotting). The subscript vector can be either a logical, character or numeric one. The character vector should contain the names of faces, the logical subscript should have the same length as the number of faces in the order in which the faces are present in the faces slot. The numeric vector can either refer to indices to the rownames of faces in the faces slot, or to surfaces bounded by longitude/latitude data. In the latter case, the the vector should contain an element with a names of at least one of the "lomax", "lamax", "lomin" or "lamin" strings (lo for longitude, la: latitude, min: minimum, max: maximum). In case a subset around the dateline is needed a larger longitude to a smaller longitude value is needed (e.g. between 150° to -150°).

The following methods are incorporated into the function: If i argument is a vector of integers, they will be interpreted as indices. If the numeric i contains either the lamin, lamax, lomin or lomax names, the subsetting will be done using the latitude-longitude coordinates outlined by these 4 values. Logical subsetting and subsetting by face names are also possible.

Examples

#create a triangular grid
g <- trigrid(c(2,2))

#make a subset pertaining to the faces
subG1 <- subset(g, c("F1", "F33"))
    
#additional way of subsetting
subG2 <- g[1:15] # selects faces F1 through F15
logicalSub<-sample(c(TRUE,FALSE), nrow(g@faces), replace=TRUE)
subG3 <- g[logicalSub]

#plot the subset in 3d space
# plot3d(subG3)

# previously mentioned case around the dateline
gDateLine<-g[c(lomax=-150, lomin=150)]
# plot3d(gDateLine)