pointkriging: interpolates regularly spaced data on a grid.
In geo: Draw and Annotate Maps, Especially Charts of the North Atlantic

Description Usage Arguments Value Side Effects See Also Examples

The function interpolates regularly spaced data on a grid. The program uses inverse distance method that takes clustering into account. Under certain conditions this method can be called kriging. For each gridpoint the program looks for neighbourhood points according to certain criteria. The program has a possibility to prevent smearing data out from one area to another where it is not wanted like between two fjords. The program has the possibility of universal kriging with the drift in lat,lon or due to an external variable.

pointkriging(lat, lon, z, xgr, vagram, maxnumber = 16, scale = "km",
  option = 1, maxdist = 0, rat = 3, nb = 8, set = 0, areas = 0,
  varcalc = F, sill = 0, minnumber = 2, suboption = 1, outside = T,
  degree = 0, lognormal = F, zeroset = F)

`lat`	Latitude of datapoints.
`lon`	Longitude of datapoints.
`z`	Values at datapoints.
`xgr`	Description of the grid. Can be output from program grid or just a list with components \$lat and \$lon.
`vagram`	Components of the variogram, a list with a least 3 components, \$sill, \$nugget & \$rang1.
`maxnumber`	Number of neighbourhood points used , default is 16. In some cases 16 points are not found.
`scale`	Scale "km" or "miles", default is "miles".
`option`	Option used for selecting neighbourhood points. Allowed values 1,2,3 and 4. Default value is one. For further information see below.
`maxdist`	If option = 4 all points within maxdist are used. If option = 4 the default value of maxdist is the range of the variogram. maxdist has also meaning when option = 1,2 or 3. In those cases points further away from any datapoint than maxdist are set to zero, mean z or NA.
`rat`	The number of points in the first step of the search is rat*maxnumber.
`nb`	Parameter describing the extent of the area where neighbourhood points are searched in the first round. Default value is 8 which means that and area of 16x16 gridpoints is searched.
`set`	Points outside region or further away than maxdist from any datapoint are set to either zero (set=0) or mean(z) set=1 or NA set =-1.
`areas`	A list defining a number of areas. NA is between areas. Points in different areas are treated as independed. Two neighbourhood fjords could be defined as different areas so the program does not interpolate between them.
`varcalc`	If varcalc is true the estimation variance at each datapoint is calculated. Default value is F.
`sill`	Sill in variance calculations. Default value is the sill of the variogram.
`minnumber`	If number of neighbourhood points found is less than or equal to minnumber the point is considered outside the areas covered by the datapoints and set to NA,0 or mean(z)
`suboption`	If option = 4 and more than maxnumber points are found in the area the program switches to option 1, 2 or 3 in the point search. Default value is 1.
`outside`	If outside is T points further away from the area than nb*dx are excluded. dx is the grid interval. Too many points outside of the area can problems in the search because the grid is used to divide the area in squares and everything left and below the first gridpoint is for example one square.
`degree`	Degree of drift polynomial for universal kriging. 0, 1 or 2. Default 0.
`lognormal`	To be described.
`zeroset`	To be described.