griddify function

Fill a grid with irregularly spaced data

Transforms irregularly spaced xyz data into a raster object suitable to create a bathy object with regularly spaced longitudes and latitudes.

griddify(xyz, nlon, nlat)

Arguments

• xyz: 3-column matrix or data.frame containing (in this order) arbitrary longitude, latitude and altitude/depth values.
• nlon: integer. The number of unique regularly-spaced longitude values that will be used to create the grid.
• nlat: integer. The number of unique regularly-spaced latitude values that will be used to create the grid.

Details

griddify takes anys dataset with irregularly spaced xyz data and transforms it into a raster object (i.e. a grid) with user specified dimensions. griddify relies on several functions from the raster package, especially rasterize and resample. If a cell of the user-defined grig does not contain any depth/altitude value in the original xyz matrix/data.frame, a NA is added in that cell. A bilinear interpolation is then applied in order to fill in most of the missing cells. For cells of the user-defined grig containing more than one depth/altitude value in the original xyz matrix/data.frame, the mean depth/altitude value is computed.

Returns

The output of griddify is an object of class raster, with nlon unique longitude values and nlat unique latitude values.

References

Robert J. Hijmans (2015). raster: Geographic Data Analysis and Modeling. R package version 2.4-20. https://CRAN.R-project.org/package=raster

Author(s)

Eric Pante and Benoit Simon-Bouhet

See Also

read.bathy, readGEBCO.bathy, plot.bathy

Examples

# load irregularly spaced xyz data
data(irregular)
head(irregular)

# use griddify to create a 40x60 grid
reg <- griddify(irregular, nlon = 40, nlat = 60)

# switch to class "bathy"
class(reg)
bat <- as.bathy(reg)
summary(bat)

# Plot the new bathy object and overlay the original data points
plot(bat, image = TRUE, lwd = 0.1)
points(irregular$lon, irregular$lat, pch = 19, cex = 0.3, col = col2alpha(3))