| interp.im {spatstat} | R Documentation |
Interpolates the values of a pixel image at any desired location in the frame.
interp.im(Z, x, y)
Z |
Pixel image (object of class "im")
with numeric or integer values.
|
x,y |
Vectors of Cartesian coordinates. |
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.
Vector of interpolated values, with NA for points that lie
outside the domain of the image.
Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner rolf@math.unb.ca http://www.math.unb.ca/~rolf
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)