ximage

The goal of ximage is to make something like ‘image()’ and ‘rasterImage()’ but without the missing functionality and useability.

ximage supports making images from

  • numeric, character, byte matrix
  • numeric array
  • nativeRaster
  • list returned from vapour::gdal_raster_() functions which include numeric, character, byte vectors or nativeRaster

The orientation is in “raster-order”, i.e. when you’re looking at the picture it’s topleft to topright, then scan lines down each row to the bottom (like western reading and par(mfrow) order). This matches the way that spatial data readers read imagery.

Example

This is a basic example which shows you how to solve a common problem:

library(ximage)
ximage(topo)  ## plot in the index space of the matrix


## or, plot in the geographic space (we happen to know this for this matrix)
ximage(topo, extent = c(-180, 180, -90, 90), axes = F)
axis(1); axis(2);box()

ximage(logo_a)  ## plot a RGB array
#> Warning in matrix(palr::image_pal(x, col, breaks = breaks), dim(x)[1L], : data
#> length differs from size of matrix: [30400 != 76 x 100]
## plot  a native raster over the other in a different window
ximage(logo_n, extent = c(10, 20, 20, 40), add = TRUE)

ximage(topo, extent = c(40, 60, 80, 100), add = TRUE, col = hcl.colors(256))

We can get imagery from the internet, and plot it very quickly.

library(vapour)  ## quite a recent version, dev in January 2024
virtual_earth <-  "<GDAL_WMS><Service name=\"VirtualEarth\"><ServerUrl>http://a${server_num}.ortho.tiles.virtualearth.net/tiles/a${quadkey}.jpeg?g=90</ServerUrl></Service><MaxConnections>4</MaxConnections><Cache/></GDAL_WMS>"
par(mar = rep(0, 4))
px <- dev.size("px")
px[which.min(px)] <- 0

## change lon_0 and lat_0 to anywhere you like
im <- gdal_raster_nara(virtual_earth, target_ext = c(-1, 1, -1, 1) * 3e5, target_dim = px, target_crs = "+proj=laea +lon_0=147 +lat_0=-42")
#> Byte
#> 1

system.time(ximage(im, asp = 1))

#>    user  system elapsed 
#>   0.006   0.000   0.006


## crank up the size it's still fast
px <- px * 4
im <- gdal_raster_nara(virtual_earth, target_ext = c(-1, 1, -1, 1) * 3e5, target_dim = px, target_crs = "+proj=laea +lon_0=147 +lat_0=-42")
#> Byte
#> 1

system.time(ximage(im, asp = 1))

#>    user  system elapsed 
#>   0.126   0.032   0.159

Code of Conduct

Please note that the ximage project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.