R/projections.r

In ropensci/geojsonio: Convert Data from and to 'GeoJSON' or 'TopoJSON'

#' topojson projections and extensions
#'
#' @export
#' @param proj Map projection name. One of albers, albersUsa, azimuthalEqualArea,
#' azimuthalEquidistant, conicEqualArea, conicConformal, conicEquidistant, equirectangular,
#' gnomonic, mercator, orthographic, stereographic, or transverseMercator.
#' @param rotate If rotation is specified, sets the projection's three-axis rotation to the
#' specified angles yaw, pitch and roll (or equivalently longitude, latitude and roll)
#' in degrees and returns the projection. If rotation is not specified, returns the current
#' rotation which defaults `[0, 0, 0]`. If the specified rotation has only two values, rather than
#' three, the roll is assumed to be 0.
#' @param center If center is specified, sets the projection's center to the specified location, a
#' two-element array of longitude and latitude in degrees and returns the projection. If center is
#' not specified, returns the current center which defaults to (0,0)
#' @param translate If point is specified, sets the projection's translation offset to the
#' specified two-element array `[x, y]` and returns the projection. If point is not specified,
#' returns the current translation offset which defaults to `[480, 250]`. The translation offset
#' determines the pixel coordinates of the projection's center. The default translation offset
#' places (0,0) at the center of a 960x500 area.
#' @param scale If scale is specified, sets the projection's scale factor to the specified value
#' and returns the projection. If scale is not specified, returns the current scale factor which
#' defaults to 150. The scale factor corresponds linearly to the distance between projected points.
#' However, scale factors are not consistent across projections.
#' @param clipAngle If angle is specified, sets the projection's clipping circle radius to the
#' specified angle in degrees and returns the projection. If angle is null, switches to
#' antimeridian cutting rather than small-circle clipping. If angle is not specified, returns the
#' current clip angle which defaults to null. Small-circle clipping is independent of viewport
#' clipping via clipExtent.
#' @param precision If precision is specified, sets the threshold for the projection's adaptive
#' resampling to the specified value in pixels and returns the projection. This value corresponds
#' to the Douglas-Peucker distance. If precision is not specified, returns the projection's current
#' resampling precision which defaults to Math.SQRT(1/2).
#' @param parallels Depends on the projection used! See
#' https://github.com/mbostock/d3/wiki/Geo-Projections#standard-projections for help
#' @param clipExtent If extent is specified, sets the projection's viewport clip extent to the
#' specified bounds in pixels and returns the projection. The extent bounds are specified as an
#' array `[[x0, y0], [x1, y1]]`, where x0 is the left-side of the viewport, y0 is the top, x1 is
#' the right and y1 is the bottom. If extent is null, no viewport clipping is performed. If extent
#' is not specified, returns the current viewport clip extent which defaults to null. Viewport
#' clipping is independent of small-circle clipping via clipAngle.
#' @param invert Projects backward from Cartesian coordinates (in pixels) to spherical coordinates
#' (in degrees). Returns an array `[longitude, latitude]` given the input array `[x, y]`.
#' @examples
#' projections(proj = "albers")
#' projections(proj = "albers", rotate = "[98 + 00 / 60, -35 - 00 / 60]", scale = 5700)
#' projections(proj = "albers", scale = 5700)
#' projections(proj = "albers", translate = "[55 * width / 100, 52 * height / 100]")
#' projections(proj = "albers", clipAngle = 90)
#' projections(proj = "albers", precision = 0.1)
#' projections(proj = "albers", parallels = "[30, 62]")
#' projections(proj = "albers", clipExtent = "[[105 - 87, 40], [105 + 87 + 1e-6, 82 + 1e-6]]")
#' projections(proj = "albers", invert = 60)
#' projections("orthographic")
projections <- function(proj, rotate = NULL, center = NULL, translate = NULL,
                        scale = NULL, clipAngle = NULL, precision = NULL, parallels = NULL, clipExtent = NULL,
                        invert = NULL) {
  if (missing(proj)) stop("You must provide a character string to 'proj'", call. = FALSE)
  vals <- list(
    albers = "d3.geo.albers()%s",
    albersUsa = "d3.geo.albersUsa()",
    azimuthalEqualArea = "d3.geo.azimuthalEqualArea()",
    azimuthalEquidistant = "d3.geo.azimuthalEquidistant()",
    conicEqualArea = "d3.geo.conicEqualArea()",
    conicConformal = "d3.geo.conicConformal()",
    conicEquidistant = "d3.geo.conicEquidistant()",
    equirectangular = "d3.geo.equirectangular()",
    gnomonic = "d3.geo.gnomonic()",
    mercator = "d3.geo.mercator()",
    orthographic = "d3.geo.orthographic()",
    stereographic = "d3.geo.stereographic()",
    transverseMercator = "d3.geo.transverseMercator()"
  )
  got <- vals[[proj]]
  if (is.null(got)) stop("no match for 'proj' parameter input")
  args <- tg_compact(list(
    rotate = rotate, center = center,
    translate = translate, scale = scale,
    clipAngle = clipAngle, precision = precision, parallels = parallels,
    clipExtent = clipExtent, invert = invert
  ))
  out <- list()
  for (i in seq_along(args)) {
    out[i] <- sprintf(".%s(%s)", names(args[i]), args[[i]])
  }
  argstogo <- paste(out, collapse = "")
  gotgo <- if (nzchar(argstogo)) sprintf(got, argstogo) else got
  gotgo <- gsub("%s", "", gotgo)
  if (is.null(gotgo)) {
    "That projection doesn't exist, check your spelling"
  } else {
    gotgo
  }
}