Summary of available geometry — vapour_geom

Read properties of geometry from a source, optionally after SQL execution.

vapour_geom_summary(
  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)

Value

list containing the following

FID the feature id value (an integer, usually sequential)
valid_geometry logical value if a non-empty geometry is available
type integer value of geometry type from GDAL enumeration
xmin, xmax, ymin, ymax numeric values of the extent (bounding box) of each geometry

Details

Use limit_n to arbitrarily limit the number of features queried.

Examples

file <- "list_locality_postcode_meander_valley.tab"
mvfile <- system.file(file.path("extdata/tab", file), package="vapour")
vapour_geom_summary(mvfile, limit_n = 3L)
#> $FID
#> [1] 1 2 3
#> 
#> $valid_geometry
#> [1] TRUE TRUE TRUE
#> 
#> $type
#> [1] 3 6 3
#> 
#> $xmin
#> [1] 448353.3 453543.6 454839.8
#> 
#> $xmax
#> [1] 457705.8 459318.0 461042.0
#> 
#> $ymin
#> [1] 5386606 5403972 5411562
#> 
#> $ymax
#> [1] 5397352 5412505 5417892
#> 

gsum <- vapour_geom_summary(mvfile)
plot(NA, xlim = range(c(gsum$xmin, gsum$xmax), na.rm = TRUE),
         ylim = range(c(gsum$ymin, gsum$ymax), na.rm = TRUE))
rect(gsum$xmin, gsum$ymin, gsum$xmax, gsum$ymax)
text(gsum$xmin, gsum$ymin, labels = gsum$FID)