vapour_read_fids: Read feature names

In vapour: Access to the 'Geospatial Data Abstraction Library' ('GDAL')

Read feature names

Description

Obtains the internal 'Feature ID (FID)' for a data source.

Usage

vapour_read_fids(
  dsource,
  layer = 0L,
  sql = "",
  limit_n = NULL,
  skip_n = 0,
  extent = NA
)

vapour_read_names(
  dsource,
  layer = 0L,
  sql = "",
  limit_n = NULL,
  skip_n = 0,
  extent = NA
)

Arguments

dsource	data source name (path to file, connection string, URL)
layer	integer of layer to work with, defaults to the first (0) or the name of the layer
sql	if not empty this is executed against the data source (layer will be ignored)
limit_n	an arbitrary limit to the number of features scanned
skip_n	an arbitrary number of features to skip
extent	apply an arbitrary extent, only when 'sql' used (must be 'ex = c(xmin, xmax, ymin, ymax)' but sp bbox, sf bbox, and raster extent also accepted)

Details

This may be virtual (created by GDAL for the SQL interface) and may be 0- or 1- based. Some drivers have actual names, and they are persistent and arbitrary. Please use with caution, this function can return the current FIDs, but there's no guarantee of what it represents for subsequent access.

An earlier version use 'OGRSQL' to obtain these names, which was slow for some drivers and also clashed with independent use of the sql argument. vapour_read_names() is an older name, aliased to vapour_read_fids().

Value

character vector of geometry id 'names'

Examples

file <- "list_locality_postcode_meander_valley.tab"
mvfile <- system.file(file.path("extdata/tab", file), package="vapour")
range(fids <- vapour_read_names(mvfile))
length(fids)

vapour documentation built on June 22, 2024, 10:01 a.m.