proj_pipelines: Find CRS transformation pipelines

In terra: Spatial Data Analysis

Find CRS transformation pipelines

Description

Find candidate coordinate transformation pipelines between two coordinate reference systems. This can be used to examine which transformations are available, whether they require grid files, and what accuracy they provide. You can use a selected pipeline with the project methods

Usage

proj_pipelines(from, to, authority="", AOI=NULL, use="NONE", 
	grid_availability="USED", desired_accuracy=-1.0, strict_containment=FALSE)

Arguments

from	character, SpatRaster, SpatVector, or any object from which crs() can extract a CRS
to	same types as for from
authority	character. Constrain output pipelines to those from this authority (e.g. "EPSG"). Default "" means no constraint
AOI	SpatExtent. Area of interest for the transformation in degrees. For an area of interest crossing the anti-meridian, west should be greater than east, e.g. ext(150, 210, 0, 30)
use	character. One of "NONE", "BOTH", "INTERSECTION", "SMALLEST", indicating how areas of interest of source and target CRS are used. Ignored when AOI is specified
grid_availability	character. One of "USED" (grid availability is used for sorting; operations with missing grids are sorted last), "DISCARD" (discard operations if a required grid is missing), "IGNORED" (ignore grid availability; results presented as if all grids were available), or "AVAILABLE" (results presented as if grids known to PROJ were available; typical when networking is enabled)
desired_accuracy	numeric. Only return pipelines with at least this accuracy (in metres). Use -1 (the default) to impose no accuracy constraint
strict_containment	logical. If FALSE (the default), permit partial matching of the area of interest. If TRUE, the area of interest must be strictly contained

Value

A data.frame with "pipelines" and the following columns:

description

human-readable description

definition

PROJ pipeline definition string

has_inverse

logical; whether the pipeline has an inverse

accuracy

accuracy in metres; -1 indicates unknown (ballpark) accuracy

grid_count

number of grids required by this pipeline

instantiable

logical; whether the pipeline can be used (all required grids are available)

Note

Requires PROJ >= 7.1 (inc" 3). See projNetwork to enable online grid downloading.

See Also

crs, project, same.crs, projNetwork

Examples

## Not run: 
# Simple case: WGS84 to UTM zone 32N
proj_pipelines("EPSG:4326", "EPSG:32632")

# Many pipelines between NAD83/Conus Albers and WGS84
pp <- proj_pipelines("EPSG:5070", "EPSG:4326")
nrow(pp)

# Only pipelines that work without downloading grids
pp_local <- proj_pipelines("EPSG:5070", "EPSG:4326", grid_availability="DISCARD")
pp_local

# Using a SpatRaster as input
r <- rast(ncols=10, nrows=10, crs="EPSG:4326")
proj_pipelines(r, "EPSG:3857")

## End(Not run)

terra documentation built on Aug. 22, 2026, 5:07 p.m.