Bilinear and Bicubic Interpolation to Grid

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Description

This code includesa bicubic interpolation and a bilinear interpolation adapted from Numerical Recipes in C: The art of scientific computing http://www.nrbook.com/nr3/ (chapter 3... bicubic interpolation) and a bicubic interpolation from http://www.paulinternet.nl/?page=bicubic in java code.

Inputs are a list of points to interpolate to and from raster objects of class 'asc' (adehabitat package), 'RasterLayer' (raster package) or 'SpatialGridDataFrame' (sp package).

Usage

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interp2grid(mat,xout,yout,xin=NULL,yin=NULL,type=2)

Arguments

mat

a matrix of data that can be a raster matrix of class 'asc' (adehabitat package), 'RasterLayer' (raster package) or 'SpatialGridDataFrame' (sp package) NA values are not permitted.. data must be complete.

xout

a vector of data representing x coordinates of the output grid. Resulting grid must have square cell sizes if mat is of class 'asc', 'RasterLayer' or 'SpatialGridDataFrame'.

yout

a vector of data representing x coordinates of the output grid. Resulting grid must have square cell sizes if mat is of class 'asc', 'RasterLayer' or 'SpatialGridDataFrame'.

xin

a vector identifying the locations of the columns of the input data matrix. These are automatically populated if mat is of class 'asc', 'RasterLayer' or 'SpatialGridDataFrame'.

yin

a vector identifying the locations of the rows of the input data matrix. These are automatically populated if mat is of class 'asc', 'RasterLayer' or 'SpatialGridDataFrame'.

type

an integer value representing the type of interpolation method used.

1 - bilinear adapted from Numerical Recipes in C

2 - bicubic adapted from Numerical Recipes in C

3 - bicubic adapted from online java code

Value

Returns a matrix of the originating class.

Author(s)

Jeremy VanDerWal jjvanderwal@gmail.com

Examples

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tx = seq(0,3,0.1)
ty = seq(0,3,0.1)

     tmat = matrix(runif(16,1,16),nrow=4)
     txin = seq(0,3,length=4)
     tyin = seq(0,3,length=4)

     bilinear1 = interp2grid(tmat,tx,ty,txin, tyin,    type=1)
     bicubic2 = interp2grid(tmat,tx,ty,txin, tyin, type=2)
     bicubic3 = interp2grid(tmat,tx,ty,txin, tyin, type=3)

    par(mfrow=c(2,2),cex=1)
             image(tmat,main='base',zlim=c(0,16),col=heat.colors(100))
             image(bilinear1,main='bilinear',zlim=c(0,16),col=heat.colors(100))
             image(bicubic2,main='bicubic2',zlim=c(0,16),col=heat.colors(100))
             image(bicubic3,main='bicubic3',zlim=c(0,16),col=heat.colors(100))
   

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