# Distance on a grid

`gridDist.Rd`

The function calculates the distance to cells of a SpatRaster when the path has to go through the centers of the eight neighboring raster cells.

The default distance (when `scale=1`

, is meters if the coordinate reference system (CRS) of the SpatRaster is longitude/latitude (`+proj=longlat`

) and in the linear units of the CRS (typically meters) in other cases.

Distances are computed by summing local distances between cells, which are connected with their neighbors in 8 directions.

The shortest distance to the cells with the `target`

value is computed for all cells that are not `NA`

. Cells that are `NA`

cannot be traversed and are ignored, unless the target itself is `NA`

, in which case the distance to the nearest cell that is not `NA`

is computed for all cells that are `NA`

.

## Usage

```
# S4 method for class 'SpatRaster'
gridDist(x, target=0, scale=1, maxiter=50, filename="", ...)
```

## Arguments

- x
SpatRaster

- target
numeric. value of the target cells (where to compute distance to)

- scale
numeric. Scale factor. For longitude/latitude data 1 = "m" and 1000 = "km". For planar data that is also the case of the distance unit of the crs is "m"

- maxiter
numeric. The maximum number of iterations. Increase this number if you get the warning that

`costDistance`

did not converge. Only relevant when target is not`NA`

- filename
character. output filename (optional)

- ...
additional arguments as for

`writeRaster`

## Examples

```
# global lon/lat raster
r <- rast(ncol=10,nrow=10, vals=1)
r[48] <- 0
r[66:68] <- NA
d <- gridDist(r)
plot(d)
# planar
crs(r) <- "+proj=utm +zone=15 +ellps=GRS80 +datum=NAD83 +units=m +no_defs"
d <- gridDist(r)
plot(d)
# distance to cells that are not NA
rr <- classify(r, cbind(1, NA))
dd <- gridDist(rr, NA)
```