rasterImage adjusting to zero distortion

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Description

Call rasterImage to plot image from (xleft, ybottom) to either xright or ytop, shrinking one toward the center to avoid distortion.

angle specifies a rotation around the midpoint ((xleft+xright)/2, (ybottom+ytop)/2). This is different from rasterImage, which rotates around (xleft, ybottom).

NOTE: The code may change in the future. The visual image with rotation looks a little off in the examples below, but the code seems correct. If you find an example where this is obviously off, please report to the maintainer – especially if you find a fix for this.

Usage

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rasterImageAdj(image, xleft=par('usr')[1], ybottom=par('usr')[3],
     xright=par('usr')[2], ytop=par('usr')[4], angle = 0,
     interpolate = TRUE, xsub=NULL, ysub=NULL, ...)

Arguments

image

a raster object, or an object that can be coerced to one by as.raster.

xleft

a vector (or scalar) of left x positions.

ybottom

a vector (or scalar) of bottom y positions.

xright

a vector (or scalar) of right x positions.

ytop

a vector (or scalar) of top y positions.

angle

angle of rotation in degrees, anti-clockwise about the centroid of image.

NOTE: rasterImage rotates around (xleft, ybottom). rasterImage rotates around the center ((xleft+xright)/2, (ybottom+ytop)/2). See the examples.

interpolate

a logical vector (or scalar) indicating whether to apply linear interpolation to the image when drawing.

xsub, ysub

subscripts to subset image

...

graphical parameters (see par).

Details

1. imagePixels = number of (x, y) pixels in image. Do this using dim(as.raster(image))[2:1], because the first dimension of image can be either x or y depending on class(image). For example link[EBImage]{Image} returns dim with x first then y and an optional third dimension for color. A simple 3-dimensional array is assumed by rasterImage to have the y dimension first. as.raster puts all these in a standard format with y first, then x.

2. imageUnits <- c(x=xright-xleft, ytop-ybottom)

3. xyinches = (x, y) units per inch in the current plot, obtained from xyinch.

4. Compute pixel density (pixels per inch) in both x and y dimension: pixelsPerInch <- imagePixels * xyinches / imageUnits.

5. Compute imageUnitsAdj solving 4 for imageUnits and replacing pixelsPerInch by the max pixel density: imageUnitsAdj <- imagePixels * xyinches / max(pixelsPerInch).

6. (dX, dY) = imageUnitsAdj/2 = half of the (width, height) in plotting units.

7. cntr = (xleft, ybottom) + (dX, dY).

xleft0 = cntr[1]+sin((angle-90)*pi/180)*dX*sqrt(2); ybottom0= cntr[2]-cos((angle-90)*pi/180)*dY*sqrt(2);

(xright0, ytop0) = (upper right without rotation about lower left) xright0 = xleft0+imageUnitsAdj[2] ytop0 = ybottom0+imageUnitsAdj[2]

8. rasterImage(image, xleft0, ybottom0, xright0, ytop0, angle, interpolate, ...)

Value

a named vector giving the values of xleft, ybottom, xright, and ytop passed to rasterImage. (rasterImage returns NULL, at least for some inputs.) This shows the adjustment, shrinking toward the center and rotating as desired.

Author(s)

Spencer Graves

See Also

rasterImage

Examples

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# something to plot 
logo.jpg <- paste(R.home(), "doc", "html", "logo.jpg",
                  sep = .Platform$file.sep)
if(require(jpeg)){
##
## 1.  Shrink as required
##
  Rlogo <- readJPEG(logo.jpg)
  
  all.equal(dim(Rlogo), c(76, 100, 3))
  

  plot(1:2)
# default
  rasterImageAdj(Rlogo)

  plot(1:2, type='n', asp=0.75)
# Tall and thin
  rasterImage(Rlogo, 1, 1, 1.2, 2)
# Fix
  rasterImageAdj(Rlogo, 1.2, 1, 1.4, 2)

# short and wide
  rasterImage(Rlogo, 1.4, 1, 2, 1.2)
# Fix
  rasterImage(Rlogo, 1.4, 1.2, 2, 1.4)
##
## 2.  rotate 
##
#  2.1.  angle=90:  rasterImage left of rasterImageAdj
  plot(0:1, 0:1, type='n', asp=1)
  rasterImageAdj(Rlogo, .5, .5, 1, 1, 90)
  rasterImage(Rlogo, .5, .5, 1, 1, 90)
#  2.2.  angle=180:  rasterImage left and below 
  plot(0:1, 0:1, type='n', asp=1)
  rasterImageAdj(Rlogo, .5, .5, 1, 1, 180)
  rasterImage(Rlogo, .5, .5, 1, 1, 180)
#  2.3.  angle=270:  rasterImage below 
  plot(0:1, 0:1, type='n', asp=1)
  rasterImageAdj(Rlogo, .5, .5, 1, 1, 270)
  rasterImage(Rlogo, .5, .5, 1, 1, 270)
## 
## 3.  subset 
##
dim(Rlogo)
# 76 100 3
Rraster <- as.raster(Rlogo)
dim(Rraster)
# 76 100:  
# x=1:100, left to right 
# y=1:76, top to bottom 
rasterImageAdj(Rlogo, 0, 0, .5, .5, xsub=40:94)
}

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