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Shear geometries

Source: R/ddbs_affine.R
ddbs_shear.Rd

Applies a shear transformation to geometries, shifting coordinates proportionally in the X and Y directions. By default, shearing is applied relative to the centroid of all geometries; if by_feature = TRUE, each geometry is sheared relative to its own centroid.

Usage

ddbs_shear(
  x,
  x_shear = 0,
  y_shear = 0,
  by_feature = FALSE,
  conn = NULL,
  name = NULL,
  crs = NULL,
  crs_column = "crs_duckspatial",
  mode = NULL,
  overwrite = FALSE,
  quiet = FALSE
)

Arguments

x

Input spatial data. Can be:

  • A duckspatial_df object (lazy spatial data frame via dbplyr)

  • An sf object

  • A tbl_lazy from dbplyr

  • A character string naming a table/view in conn

Data is returned from this object.

x_shear

numeric value specifying the shear factor in the X direction (default = 0). For each unit in Y, X coordinates are shifted by this amount

y_shear

numeric value specifying the shear factor in the Y direction (default = 0). For each unit in X, Y coordinates are shifted by this amount

by_feature

Logical. If TRUE, the geometric operation is applied separately to each geometry. If FALSE, the geometric operation is applied to the data as a whole.

conn

A connection object to a DuckDB database. If NULL, the function runs on a temporary DuckDB database.

name

A character string of length one specifying the name of the table, or a character string of length two specifying the schema and table names. If NULL (the default), the function returns the result as an sf object

crs

Deprecated The coordinates reference system of the data. Specify if the data doesn't have a crs_column, and you know the CRS.

crs_column

Deprecated a character string of length one specifying the column storing the CRS (created automatically by ddbs_write_vector). Set to NULL if absent.

mode

Character. Controls the return type. Options:

  • "duckspatial" (default): Lazy spatial data frame backed by dbplyr/DuckDB

  • "sf": Eagerly collected sf object (uses memory)

Can be set globally via ddbs_options(mode = "...") or per-function via this argument. Per-function overrides global setting.

overwrite

Boolean. whether to overwrite the existing table if it exists. Defaults to FALSE. This argument is ignored when name is NULL.

quiet

A logical value. If TRUE, suppresses any informational messages. Defaults to FALSE.

Value

Depends on the mode argument (or global preference set by ddbs_options):

  • duckspatial (default): A duckspatial_df (lazy spatial data frame) backed by dbplyr/DuckDB.

  • sf: An eagerly collected object in R memory, that will return the same data type as the sf equivalent (e.g. sf or units vector).

When name is provided, the result is also written as a table or view in DuckDB and the function returns TRUE (invisibly).

Examples

if (FALSE) { # \dontrun{
## load packages
library(duckspatial)
library(dplyr)

# create a duckdb database in memory (with spatial extension)
conn <- ddbs_create_conn(dbdir = "memory")

## read data
countries_ddbs <- ddbs_open_dataset(
  system.file("spatial/countries.geojson", 
  package = "duckspatial")
) |>
  filter(CNTR_ID %in% c("PT", "ES", "FR", "IT"))

## store in duckdb
ddbs_write_table(conn, countries_ddbs, "countries")

## shear in X direction (creates italic-like effect)
ddbs_shear(conn = conn, "countries", x_shear = 0.3, y_shear = 0)

## shear in Y direction
ddbs_shear(conn = conn, "countries", x_shear = 0, y_shear = 0.3)

## shear in both directions
ddbs_shear(conn = conn, "countries", x_shear = 0.2, y_shear = 0.2)

## shear without using a connection
ddbs_shear(countries_ddbs, x_shear = 0.3, y_shear = 0)
} # }