R: Extracts values at points from a list of files

extract {GSIF}

R Documentation

Extracts values at points from a list of files

Description

Overlays and extracts values at points from a list of raster layers defined as file names (e.g. GeoTiffs). Extends the extract function from the raster package. Especially suitable for extracting values of a large list of rasters that have not been organized into a mosaick (a virtual stack), for example a list of Landsat scenes.

Usage

## S4 method for signature 'SpatialPoints,character'
extract(x, y, 
   path=".", ID = "SOURCEID", 
   method = "simple", is.pattern = FALSE, force.projection = TRUE, 
   NAflag = "", show.progress=TRUE, isFactor=FALSE, ...)
## S4 method for signature 'SpatialPointsDataFrame,character'
extract(x, y, 
   path = ".", ID = "SOURCEID", 
   method = "simple", is.pattern = FALSE, force.projection = TRUE, 
   NAflag = "", show.progress=TRUE, isFactor=FALSE, ...)

Arguments

`x`	object of class `"SpatialPoints*"`
`y`	character; list of files that can be read using the `raster` function
`path`	optional working directory where the files are stored
`ID`	character; column name for the unique identifier (if object is of class `"SpatialPoints"` `"SOURCEID"` column is automatically generated)
`method`	character; resampling method (see `raster::extract`)
`is.pattern`	logical; specifies whether the list is a pattern
`force.projection`	logical; specifies whether the reprojection should be ignored
`NAflag`	character; missing value flag (all missing values are removed by default)
`show.progress`	logical; specifies whether to display the progress bar
`isFactor`	logical; turns aggregation on off for factor type variable
`...`	additional arguments that can be passed to the `raster::extract` function

Note

The method will try to reproject the values to the native coordinate system, hence it is highly advisible to embed the proj4 string into the GeoTiffs. If both x and y are in the same coordinate system, then reprojection can be turned off by setting force.projection = FALSE. In the case is.pattern = TRUE (search by pattern), missing values are removed by default and if multiple rasters covering the same area are found, values are aggregated to the mean value.

Author(s)