get_pixel_line() converts geospatial coordinates to pixel/line (raster
column, row numbers).
The upper left corner pixel is the raster origin (0,0) with column, row
increasing left to right, top to bottom.
Arguments
- xy
Numeric matrix of geospatial x,y coordinates in the same spatial reference system as
gt(or two-column data frame that will be coerced to numeric matrix).- gt
Either a numeric vector of length six containing the affine geotransform for the raster, or an object of class
GDALRasterfrom which the geotransform will be obtained (see Note).
Note
This function applies the inverse geotranform to the input points. If gt
is given as the numeric vector, no bounds checking is done (i.e., min
pixel/line could be less than zero and max pixel/line could be greater than
the raster x/y size). If gt is obtained from an object of class
GDALRaster, then NA is returned for points that fall outside the
raster extent and a warning emitted giving the number points that were
outside. This latter case is equivalent to calling the $get_pixel_line()
class method on the GDALRaster object (see Examples).
Examples
pt_file <- system.file("extdata/storml_pts.csv", package="gdalraster")
# id, x, y in NAD83 / UTM zone 12N
pts <- read.csv(pt_file)
print(pts)
#> id xcoord ycoord
#> 1 1 324650.9 5103344
#> 2 2 324171.0 5103034
#> 3 3 323533.4 5103329
#> 4 4 325220.0 5103508
#> 5 5 325703.1 5102377
#> 6 6 326297.8 5103924
#> 7 7 325520.4 5104146
#> 8 8 326247.7 5102506
#> 9 9 327711.7 5104476
#> 10 10 324181.7 5103901
raster_file <- system.file("extdata/storm_lake.lcp", package="gdalraster")
ds <- new(GDALRaster, raster_file)
gt <- ds$getGeoTransform()
get_pixel_line(pts[, -1], gt)
#> [,1] [,2]
#> [1,] 39 57
#> [2,] 23 68
#> [3,] 1 58
#> [4,] 58 52
#> [5,] 74 90
#> [6,] 94 38
#> [7,] 68 31
#> [8,] 92 85
#> [9,] 141 20
#> [10,] 23 39
# or, using the class method
ds$get_pixel_line(pts[, -1])
#> [,1] [,2]
#> [1,] 39 57
#> [2,] 23 68
#> [3,] 1 58
#> [4,] 58 52
#> [5,] 74 90
#> [6,] 94 38
#> [7,] 68 31
#> [8,] 92 85
#> [9,] 141 20
#> [10,] 23 39
# add a point outside the raster extent
pts[11, ] <- c(11, 323318, 5105104)
get_pixel_line(pts[, -1], gt)
#> [,1] [,2]
#> [1,] 39 57
#> [2,] 23 68
#> [3,] 1 58
#> [4,] 58 52
#> [5,] 74 90
#> [6,] 94 38
#> [7,] 68 31
#> [8,] 92 85
#> [9,] 141 20
#> [10,] 23 39
#> [11,] -6 -1
# with bounds checking on the raster extent
ds$get_pixel_line(pts[, -1])
#> Warning: 1 point(s) outside the raster extent, NA returned
#> [,1] [,2]
#> [1,] 39 57
#> [2,] 23 68
#> [3,] 1 58
#> [4,] 58 52
#> [5,] 74 90
#> [6,] 94 38
#> [7,] 68 31
#> [8,] 92 85
#> [9,] 141 20
#> [10,] 23 39
#> [11,] NA NA
ds$close()