# Change the coordinate reference system

`project.Rd`

Change the coordinate reference system ("project") of a SpatVector, SpatRaster or a matrix with coordinates.

## Usage

```
# S4 method for SpatVector
project(x, y, partial = FALSE)
# S4 method for SpatRaster
project(x, y, method, mask=FALSE, align_only=FALSE, res=NULL,
origin=NULL, threads=FALSE, filename="", ..., use_gdal=TRUE, by_util = FALSE)
# S4 method for SpatExtent
project(x, from, to)
# S4 method for matrix
project(x, from, to)
```

## Arguments

- x
SpatRaster, SpatVector, SpatExtent or matrix (with x and y columns) whose coordinates to project

- y
if (

`x`

is a SpatRaster, the preferred approach is for`y`

to be a SpatRaster as well, serving as a template for the geometry (extent and resolution) of the output SpatRaster. Alternatively, you can provide a coordinate reference system (CRS) description.You can use the following formats to define coordinate reference systems: WKT, PROJ.4 (e.g.,

`+proj=longlat +datum=WGS84`

), or an EPSG code (e.g.,`"epsg:4326"`

). But note that the PROJ.4 notation has been deprecated, and you can only use it with the WGS84/NAD83 and NAD27 datums. Other datums are silently ignored.If

`x`

is a SpatVector, you can provide a crs definition as discussed above, or any other object from which such a crs can be extracted with`crs`

- partial
logical. If

`TRUE`

, geometries that can only partially be represented in the output crs are included in the output- method
character. Method used for estimating the new cell values of a SpatRaster. One of:

`near`

: nearest neighbor. This method is fast, and it can be the preferred method if the cell values represent classes. It is not a good choice for continuous values. This is used by default if the first layer of`x`

is categorical.`bilinear`

: bilinear interpolation. This is the default if the first layer of`x`

is numeric (not categorical).`cubic`

: cubic interpolation.`cubicspline`

: cubic spline interpolation.`lanczos`

: Lanczos windowed sinc resampling.`sum`

: the weighted sum of all non-NA contributing grid cells.`min, q1, med, q3, max, average, mode, rms`

: the minimum, first quartile, median, third quartile, maximum, mean, mode, or root-mean-square value of all non-NA contributing grid cells.- mask
logical. If

`TRUE`

, mask out areas outside the input extent. For example to avoid data wrapping around the date-line (see example with Robinson projection). To remove cells that are`NA`

in`y`

(if`y`

is a SpatRaster) you can use the`mask method`

after calling`project`

(this function)- align_only
logical. If

`TRUE`

, and`y`

is a SpatRaster, the template is used for the spatial resolution and origin, but the extent is set such that all of the extent of`x`

is included- res
numeric. Can be used to set the resolution of the output raster if

`y`

is a CRS- origin
numeric. Can be used to set the origin of the output raster if

`y`

is a CRS- threads
logical. If

`TRUE`

multiple threads are used (faster for large files)- filename
character. Output filename

- ...
additional arguments for writing files as in

`writeRaster`

- use_gdal
logical. If

`TRUE`

the GDAL-warp algorithm is used. Otherwise a slower internal algorithm is used that may be more accurate if there is much variation in the cell sizes of the output raster. Only the`near`

and`bilinear`

algorithms are available for the internal algorithm- by_util
logical. If

`TRUE`

and`gdal=TRUE`

, the GDAL warp utility is used- from
character. Coordinate reference system of

`x`

- to
character. Output coordinate reference system

## Note

The PROJ.4 notation of coordinate reference systems has been partly deprecated in the GDAL/PROJ library that is used by this function. You can still use this notation, but *only* with the WGS84 datum. Other datums are silently ignored.

Transforming (projecting) raster data is fundamentally different from transforming vector data. Vector data can be transformed and back-transformed without loss in precision and without changes in the values. This is not the case with raster data. In each transformation the values for the new cells are estimated in some fashion. Therefore, if you need to match raster and vector data for analysis, you should generally transform the vector data.

When using this method with a `SpatRaster`

, the preferable approach is to provide a template `SpatRaster`

as argument `y`

. The template is then another raster dataset that you want your data to align with. If you do not have a template to begin with, you can do `project(rast(x), crs)`

and then manipulate the output to get the template you want. For example, where possible use whole numbers for the extent and resolution so that you do not have to worry about small differences in the future. You can use commands like `dim(z) = c(180, 360)`

or `res(z) <- 100000`

.

The output resolution should generally be similar to the input resolution, but there is no "correct" resolution in raster transformation. It is not obvious what this resolution is if you are using lon/lat data that spans a large North-South extent.

## Examples

```
## SpatRaster
a <- rast(ncols=40, nrows=40, xmin=-110, xmax=-90, ymin=40, ymax=60,
crs="+proj=longlat +datum=WGS84")
values(a) <- 1:ncell(a)
newcrs="+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +datum=WGS84"
b <- rast(ncols=94, nrows=124, xmin=-944881, xmax=935118, ymin=4664377, ymax=7144377, crs=newcrs)
w <- project(a, b)
## SpatVector
f <- system.file("ex/lux.shp", package="terra")
v <- vect(f)
crs(v, proj=TRUE)
#> [1] "+proj=longlat +datum=WGS84 +no_defs"
cat(crs(v), "\n")
#> GEOGCRS["WGS 84",
#> DATUM["World Geodetic System 1984",
#> ELLIPSOID["WGS 84",6378137,298.257223563,
#> LENGTHUNIT["metre",1]]],
#> PRIMEM["Greenwich",0,
#> ANGLEUNIT["degree",0.0174532925199433]],
#> CS[ellipsoidal,2],
#> AXIS["geodetic latitude (Lat)",north,
#> ORDER[1],
#> ANGLEUNIT["degree",0.0174532925199433]],
#> AXIS["geodetic longitude (Lon)",east,
#> ORDER[2],
#> ANGLEUNIT["degree",0.0174532925199433]],
#> ID["EPSG",4326]]
project(v, "+proj=moll")
#> class : SpatVector
#> geometry : polygons
#> dimensions : 12, 6 (geometries, attributes)
#> extent : 437476.4, 497805.3, 5815524, 5892478 (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=moll +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
#> names : ID_1 NAME_1 ID_2 NAME_2 AREA POP
#> type : <num> <chr> <num> <chr> <num> <int>
#> values : 1 Diekirch 1 Clervaux 312 18081
#> 1 Diekirch 2 Diekirch 218 32543
#> 1 Diekirch 3 Redange 259 18664
project(v, "EPSG:2169")
#> class : SpatVector
#> geometry : polygons
#> dimensions : 12, 6 (geometries, attributes)
#> extent : 49540.31, 105922, 57009.53, 138631.1 (xmin, xmax, ymin, ymax)
#> coord. ref. : LUREF / Luxembourg TM (EPSG:2169)
#> names : ID_1 NAME_1 ID_2 NAME_2 AREA POP
#> type : <num> <chr> <num> <chr> <num> <int>
#> values : 1 Diekirch 1 Clervaux 312 18081
#> 1 Diekirch 2 Diekirch 218 32543
#> 1 Diekirch 3 Redange 259 18664
```