# ipdw

The `R`

package ipdw provides
the functionality to perform interpolation of georeferenced point data
using inverse path distance weighting. Interpolation is accomplished in
two steps. First, path distances are calculated from each georeferenced
(measurement) point to each prediction point. Path distances, which
honor barriers in the landscape, are calculated based on cell-to-cell
movement through an underlying `Raster`

object that
represents movement cost. These path distances are subsequently used as
interpolation weights. The two-step routine follows the order of
operations described in Suominen et al. (2010) substituting the ESRI
path distance algorithm with the `gdistance`

wrapped version
of the `igraph`

adjacency algorithm.

The ipdw package was developed with coastal marine applications in
mind where path distances (as the fish swims) rather than Euclidean (as
the crow flies) distances more accurately represent spatial
connectivity. Interpolation of sparse grids in coastal areas otherwise
end up bleeding through land areas.

## Installation

### Stable version from CRAN

### or development version from
GitHub

```
install.packages("devtools") # package devtools needed
devtools::install_github("jsta/ipdw")
```

## Examples

**see** vignette

## References

**J. Stachelek and Christopher J. Madden (2015)**.
Application of Inverse Path Distance weighting for high density spatial
mapping of coastal water quality patterns. *International Journal of
Geographical Information Science* preprint | journal

**Tapio Suominen, Harri Tolvanen, and Risto Kalliola
(2010)**. Surface layer salinity gradients and flow patterns in
the archipelago coast of SW Finland, northern Baltic Sea. *Marine
Environmental Research* journal