image2lz {fields}R Documentation

Some simple functions for subsetting images

Description

These function help in subsetting a image or reducing it size by averaging adjecent cells.

Usage


crop.image(obj, loc=NULL,...)
half.image(obj)
get.rectangle()

Arguments

obj A list in image format with the usual x,y defining the grid and z a matrix of image values.
loc A 2 column matrix of locations within the image region that define the subset. If not specified then the image is plotted and the rectangle can be specified interactively.
... Graphics arguments passed to image.plot. This is only relevant when loc is NULLand the locator function is called.

Details

If loc has more than 2 rows then the largest rectangle containing the locations is used.

Author(s)

Doug Nychka

See Also

drape.plot, image.plot

Examples

data(RMelevation)

loc<- rbind( c(-106.5, 40.8),
             c(-103.9, 37.5))

# extract elevations for just CO frontrange.
FR<- crop.image(RMelevation, loc)
#  check:   image.plot( FR)

# average cells  4 to 1 by doing this twice!
 half.image( RMelevation)-> temp
 half.image( temp)-> temp

# extract the this averaged image
 FR2<- crop.image(temp, loc)
 zr<- range( FR$z)
 set.panel( 1,2)
 image.plot( FR, zlim =zr, horizontal=TRUE)
 image( FR2, zlim =zr, col=tim.colors())
[Package fields version 5.02 Index]