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Apply an affine transformation to geometries

Source: R/ddbs_affine.R
ddbs_affine.Rd

Applies an affine transformation to geometries using a 2x3 or 3x4 matrix.

Usage

ddbs_affine(
  x,
  matrix,
  conn = NULL,
  name = NULL,
  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.

matrix

A numeric matrix specifying the transformation:

  • 2x3: 2D transformation with rows [a, b, xoff] and [d, e, yoff]

  • 3x4: 3D transformation with rows [a, b, c, xoff], [d, e, f, yoff], and [g, h, i, zoff]

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), no table is written and the result is returned as a duckspatial_df or sf object, depending on mode

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 package
library(duckspatial)

## read data
argentina_ddbs <- ddbs_open_dataset(
  system.file("spatial/argentina.geojson",
  package = "duckspatial")
)

## 2D translation (shift x by 1, y by 2)
mat_2d <- matrix(c(1, 0, 1,
                   0, 1, 2), nrow = 2, byrow = TRUE)
ddbs_affine(argentina_ddbs, mat_2d)

## 2D scaling (scale x by 2, y by 3)
mat_scale <- matrix(c(2, 0, 0,
                      0, 3, 0), nrow = 2, byrow = TRUE)
ddbs_affine(argentina_ddbs, mat_scale)

## 3D transformation
mat_3d <- matrix(c(1, 0, 0, 1,
                   0, 1, 0, 2,
                   0, 0, 1, 0), nrow = 3, byrow = TRUE)
ddbs_affine(argentina_ddbs, mat_3d)
} # }