interp.im

From spatstat v1.41-1 by Adrian Baddeley

Interpolate a Pixel Image

Interpolates the values of a pixel image at any desired location in the frame.

Keywords: manip, spatial

Usage

interp.im(Z, x, y=NULL)

Arguments

Z: Pixel image (object of class "im") with numeric or integer values.
x,y: Vectors of Cartesian coordinates. Alternatively x can be a point pattern and y can be missing.

Details

A value at each location (x[i],y[i]) will be interpolated using the pixel values of Z at the four surrounding pixel centres, by simple bilinear interpolation.

At the boundary (where (x[i],y[i]) is not surrounded by four pixel centres) the value at the nearest pixel is taken.

The arguments x,y can be anything acceptable to xy.coords.

Value

Vector of interpolated values, with NA for points that lie outside the domain of the image.

Examples

opa <- par(mfrow=c(1,2))
   # coarse image
   V <- as.im(function(x,y) { x^2 + y }, owin(), dimyx=10)
   plot(V, main="coarse image", col=terrain.colors(256))

   # lookup value at location (0.5,0.5)
   V[list(x=0.5,y=0.5)]
   # interpolated value at location (0.5,0.5)
   interp.im(V, 0.5, 0.5)
   # true value is 0.75

   # how to obtain an interpolated image at a desired resolution
   U <- as.im(interp.im, W=owin(), Z=V, dimyx=256)
   plot(U, main="interpolated image", col=terrain.colors(256))
   par(opa)

Documentation reproduced from package spatstat, version 1.41-1, License: GPL (>= 2)

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