disagg: Coerce as multipart GVector to a singlepart GVector

In adamlilith/fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

Coerce as multipart GVector to a singlepart GVector

Description

GVectors can contain a mix of "singlepart" and "multipart" features. A singlepart feature is a single point, set of connected line segments, or a polygon. A multipart feature is a set of lines, sets of connected line segments, or set of polygons that are treated as a single feature. This function converts all multipart features to singlepart features. If the GVector has an attribute table, rows will be duplicated so that each of the new GVector's geometries have the rows that correspond to their "parent" geometries.

If you want to "split" cells of a GRaster into smaller cells, use aggregate().

Usage

## S4 method for signature 'GVector'
disagg(x)

Arguments

x	A GVector.

Value

A GVector.

See Also

aggregate()

Examples

if (grassStarted()) {

# Setup
library(terra)

# Example data
madElev <- fastData("madElev")
madCoast4 <- fastData("madCoast4")

### aggregating a GRaster
#########################

# Convert:
elev <- fast(madElev)

### Aggregate GRaster by same factor in 2 dimensions
# fasterRaster
agg2 <- aggregate(elev, 2, "mean")
agg2

# Compare rasters aggregated by fasterRaster and terra.
# These should be the same.
agg2terra <- aggregate(madElev, 2)

agg2 <- rast(agg2)
agg2 <- extend(agg2, agg2terra)
agg2 - agg2terra # value is ~0

### Aggregate GRaster by a non-integer factor in 2 dimensions
# fasterRaster
agg2.9 <- aggregate(elev, 2.9, "mean")
agg2.9

# terra
agg2.9terra <- aggregate(madElev, 2.9, "mean")
agg2.9terra

# Compare rasters aggregated by fasterRaster and terra.
# These should be different.
res(agg2.9)
res(agg2.9terra) # terra rounds aggregation factor down
2 * res(madElev) # original resolution multiplied by 2

### Aggregate GRaster by different factor in 2 dimensions
agg2x3 <- aggregate(elev, c(2, 3), "mean")
agg2x3

### aggregating a GVector
#########################

madCoast4 <- fastData("madCoast4")

# Convert:
coast4 <- fast(madCoast4)

# Aggregate and disaggregate:
aggCoast <- aggregate(coast4)
disaggCoast <- disagg(coast4)

ngeom(coast4)
ngeom(aggCoast)
ngeom(disaggCoast)

# plot
oldpar <- par(mfrow = c(1, 3))
plot(coast4, main = "Original", col = 1:nrow(coast4))
plot(aggCoast, main = "Aggregated", col = 1:nrow(aggCoast))
plot(disaggCoast, main = "Disaggregated", col = 1:nrow(disaggCoast))
par(oldpar)

}

adamlilith/fasterRaster documentation built on Oct. 26, 2024, 4:06 p.m.