landsat (version 1.1.2)

geoshift: Shift and pad an image

Description

Shifts an image vertically or horizontally and adds a padded border.

Usage

geoshift(mat, padx, pady, shiftx, shifty, nodata = NA)

Value

Returns data in the same format as the function was given: matrix, data frame, or SpatialGridDataFrame.

Arguments

mat

A matrix, data frame or SpatialGridDataFrame

padx

Number of pixels to add as padding in the x direction on each side of the image (along the x-axis). Should be larger than the number of pixels to shift to avoid data loss.

pady

Number of pixels to add as padding in the y direction on each side of the image (along the y-axis). Should be larger than the number of pixels to shift to avoid data loss.

shiftx

Number of pixels to shift (positive or negative) in the x direction (along the x-axis).

shifty

Number of pixels to shift (positive or negative) in the y direction (along the y-axis).

nodata

Value to use for missing data.

Author

Sarah Goslee

Details

This function can be used to correct spatially-referenced images that are off by a few pixels in the x or y directions. It does not warp an image, only slide it. Adding padding to the outside edge makes it possible to match several images even if they are not stored with georeferecing information. geoshift() can be used in conjunction with georef() to automatically match up geospatial images. Note: directions are relative to the image as displayed by the image() command, and not the underlying matrix representation.

See Also

georef

Examples

testmat <- matrix(1:9, 3, 3)
geoshift(testmat, 5, 10, 0, 0)
geoshift(testmat, 5, 10, 2, 2)

# to use for georeferencing
data(nov3)
data(july3)
july.shift <- georef(nov3, july3, maxdist=50) # match july to november
july3.corr <- geoshift(july3, padx=50, pady=50, july.shift$shiftx, july.shift$shifty)

# only need to run georef once for a particular date
# use the same correction for all bands
data(july4)
july4.corr <- geoshift(july4, padx=50, pady=50, july.shift$shiftx, july.shift$shifty)