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Shear geometries

Source: R/ddbs_affine.R
ddbs_shear.Rd

Applies a shear transformation to geometries from a sf object or a DuckDB table. Returns the result as an sf object or creates a new table in the database. Shearing skews the geometry by shifting coordinates proportionally.

Usage

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

Arguments

x

An sf spatial object. Alternatively, it can be a string with the name of a table with geometry column within the DuckDB database 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 (default), 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

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

crs_column

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

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

an sf object or TRUE (invisibly) for table creation

Examples

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

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

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

## store in duckdb
ddbs_write_vector(conn, countries_sf, "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_sf, x_shear = 0.3, y_shear = 0)
} # }