g_util: Geometry utility functions operating on WKB or WKT
In gdalraster: Bindings to 'GDAL'

g_util

R Documentation

Geometry utility functions operating on WKB or WKT

Description

These functions operate on input geometries in OGC WKB or WKT format to perform various manipulations for utility purposes.

Usage

g_make_valid(
  geom,
  method = "LINEWORK",
  keep_collapsed = FALSE,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_normalize(
  geom,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_set_3D(
  geom,
  is_3d,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_set_measured(
  geom,
  is_measured,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_swap_xy(
  geom,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

Arguments

`geom`	Either a raw vector of WKB or list of raw vectors, or a character vector containing one or more WKT strings.
`method`	Character string. One of `"LINEWORK"` (the default) or `"STRUCTURE"` (requires GEOS >= 3.10 and GDAL >= 3.4). See Details.
`keep_collapsed`	Logical value, applies only to the STRUCTURE method. Defaults to `FALSE`. See Details.
`as_wkb`	Logical value, `TRUE` to return the output geometry in WKB format (the default), or `FALSE` to return as WKT.
`as_iso`	Logical value, `TRUE` to export as ISO WKB/WKT (ISO 13249 SQL/MM Part 3), or `FALSE` (the default) to export as "Extended WKB/WKT".
`byte_order`	Character string specifying the byte order when output is WKB. One of `"LSB"` (the default) or `"MSB"` (uncommon).
`quiet`	Logical value, `TRUE` to suppress warnings. Defaults to `FALSE`.
`is_3d`	Logical value, `TRUE` if the input geometries should have a Z dimension, or `FALSE` to remove the Z dimension.
`is_measured`	Logical value, `TRUE` if the input geometries should have a M dimension, or `FALSE` to remove the M dimension.

Details

These functions use the GEOS library via GDAL headers.

g_make_valid() attempts to make an invalid geometry valid without losing vertices. Already-valid geometries are cloned without further intervention. Wrapper of OGR_G_MakeValidEx() in the GDAL API. Requires GEOS >= 3.8 library. If GDAL is built without GEOS >= 3.8, this function will return a clone of the input geometry if it is valid, or NULL (as_wkb = TRUE) / NA (as_wkb = FALSE) if it is invalid. For detailed explanations of geometry validity checking and repair, see https://gdal.org/en/latest/user/geometry_validity.html.

"LINEWORK" is the default method, which combines all rings into a set of noded lines and then extracts valid polygons from that linework (requires GEOS >= 3.10 and GDAL >= 3.4). The "STRUCTURE" method first makes all rings valid, then merges shells and subtracts holes from shells to generate a valid result. Assumes that holes and shells are correctly categorized.
keep_collapsed only applies to the "STRUCTURE" method:
- FALSE (the default): collapses are converted to empty geometries
- TRUE: collapses are converted to a valid geometry of lower dimension

g_normalize() organizes the elements, rings, and coordinate order of geometries in a consistent way, so that geometries that represent the same object can be easily compared. Wrapper of OGR_G_Normalize() in the GDAL API. Requires GDAL >= 3.3. Normalization ensures the following:

Lines are oriented to have smallest coordinate first (apart from duplicate endpoints)
Rings start with their smallest coordinate (using XY ordering)
Polygon shell rings are oriented clockwise, and holes counter-clockwise
Collection elements are sorted by their first coordinate

g_set_3D() adds or removes the explicit Z coordinate dimension. Removing the Z coordinate dimension of a geometry will remove any existing Z values. Adding the Z dimension to a geometry collection, a compound curve, a polygon, etc. will affect the children geometries. Wrapper of OGR_G_Set3D() in the GDAL API.

g_set_measured() adds or removes the explicit M coordinate dimension. Removing the M coordinate dimension of a geometry will remove any existing M values. Adding the M dimension to a geometry collection, a compound curve, a polygon, etc. will affect the children geometries. Wrapper of OGR_G_SetMeasured() in the GDAL API.

g_swap_xy() swaps x and y coordinates of the input geometry. Wrapper of OGR_G_SwapXY() in the GDAL API.

Value

A geometry as WKB raw vector or WKT string, or a list/character vector of geometries as WKB/WKT with length equal to length(geom). NULL is returned with a warning if WKB input cannot be converted into an OGR geometry object, or if an error occurs in the call to the underlying OGR API (see Note).

Note

MakeValid() in GDAL >= 3.13: Certain geometries cannot be read using GEOS, e.g., if Polygon rings are not closed or do not contain enough vertices. If a geometry cannot be read by GEOS, NULL will be returned. Starting with GDAL 3.13, GDAL will attempt to modify these geometries such that they can be read and repaired by GEOS.

Examples

## g_make_valid() requires GEOS >= 3.8, otherwise is only a validity test
geos_version()

# valid
wkt <- "POINT (0 0)"
g_make_valid(wkt, as_wkb = FALSE)

# invalid to valid
wkt <- "POLYGON ((0 0,10 10,0 10,10 0,0 0))"
g_make_valid(wkt, as_wkb = FALSE)

# invalid, note that GDAL >= 3.13 will modify to valid in this case
wkt <- "LINESTRING (0 0)"
# NULL if GDAL < 3.13, or "POINT (0 0)" with GDAL >= 3.13:
g_make_valid(wkt)

## g_normalize() requires GDAL >= 3.3
if (gdal_version_num() >= gdal_compute_version(3, 3, 0)) {
  g <- "POLYGON ((0 1,1 1,1 0,0 0,0 1))"
  g_normalize(g) |> g_wk2wk()
}

## set 3D / set measured
pt_xyzm <- g_create("POINT", c(1, 9, 100, 2000))

g_wk2wk(pt_xyzm, as_iso = TRUE)

g_set_3D(pt_xyzm, is_3d = FALSE) |> g_wk2wk(as_iso = TRUE)

g_set_measured(pt_xyzm, is_measured = FALSE) |> g_wk2wk(as_iso = TRUE)

## swap XY
g <- "GEOMETRYCOLLECTION(POINT(1 2),
                         LINESTRING(1 2,2 3),
                         POLYGON((0 0,0 1,1 1,0 0)))"

g_swap_xy(g, as_wkb = FALSE)

gdalraster documentation built on May 4, 2026, 9:06 a.m.