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| Original file line number | Diff line number | Diff line change |
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@@ -145,3 +145,5 @@ Collate: | |
| 'deprecated.R' | ||
| 'z_range.R' | ||
| 'm_range.R' | ||
| 'shift_longitude.R' | ||
| 'make_grid.R' | ||
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,166 @@ | ||
| #' Create a regular tesselation over the bounding box of an sf or sfc object | ||
| #' | ||
| #' Create a square or hexagonal grid over the bounding box of an sf or sfc object | ||
| #' @param x object of class \link{sf} or \link{sfc} | ||
| #' @param cellsize target cellsize | ||
| #' @param offset numeric of lengt 2; lower left corner coordinates (x, y) of the grid | ||
| #' @param n integer of length 1 or 2, number of grid cells in x and y direction (columns, rows) | ||
| #' @param crs object of class \code{crs}; coordinate reference system of the target of the target grid in case argument \code{x} is missing, if \code{x} is not missing, its crs is inherited. | ||
| #' @param what character; one of: \code{"polygons"}, \code{"corners"}, or \code{"centers"} | ||
| #' @param square logical; if \code{FALSE}, create hexagonal grid | ||
| #' @param flat_topped logical; if \code{TRUE} generate flat topped hexagons, else generate pointy topped | ||
| #' @return Object of class \code{sfc} (simple feature geometry list column) with, depending on \code{what} and \code{square}, | ||
| #' square or hexagonal polygons, corner points of these polygons, or center points of these polygons. | ||
| #' @examples | ||
| #' plot(st_make_grid(what = "centers"), axes = TRUE) | ||
| #' plot(st_make_grid(what = "corners"), add = TRUE, col = 'green', pch=3) | ||
| #' sfc = st_sfc(st_polygon(list(rbind(c(0,0), c(1,0), c(1,1), c(0,0))))) | ||
| #' plot(st_make_grid(sfc, cellsize = .1, square = FALSE)) | ||
| #' plot(sfc, add = TRUE) | ||
| #' # non-default offset: | ||
| #' plot(st_make_grid(sfc, cellsize = .1, square = FALSE, offset = c(0, .05 / (sqrt(3)/2)))) | ||
| #' plot(sfc, add = TRUE) | ||
| #' @export | ||
| st_make_grid = function(x, | ||
| cellsize = c(diff(st_bbox(x)[c(1,3)]), diff(st_bbox(x)[c(2,4)]))/n, | ||
| offset = st_bbox(x)[c("xmin", "ymin")], n = c(10, 10), | ||
| crs = if (missing(x)) NA_crs_ else st_crs(x), | ||
| what = "polygons", square = TRUE, flat_topped = FALSE) { | ||
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| if (missing(x) && missing(cellsize) && missing(offset) | ||
| && missing(n) && missing(crs)) # create global 10 x 10 degree grid | ||
| return(st_make_grid(cellsize = c(10,10), offset = c(-180,-90), n = c(36,18), | ||
| crs = st_crs(4326), what = what)) | ||
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| if (! square) { # hexagons: | ||
| hex = make_hex_grid(x, dx = cellsize[1]/sqrt(3), pt = offset, what = what, | ||
| flat_topped = flat_topped) | ||
| if (what == "corners") | ||
| hex = st_cast(hex, "POINT")[x] | ||
| return(hex) | ||
| } | ||
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| bb = if (!missing(n) && !missing(offset) && !missing(cellsize)) { | ||
| cellsize = rep(cellsize, length.out = 2) | ||
| n = rep(n, length.out = 2) | ||
| bb_wrap(c(offset, offset + n * cellsize)) | ||
| } else | ||
| st_bbox(x) | ||
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| cellsize_missing = if (! missing(cellsize)) { | ||
| cellsize = rep(cellsize, length.out = 2) | ||
| FALSE | ||
| } else | ||
| TRUE | ||
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| if (missing(n)) { | ||
| nx = ceiling((bb[3] - offset[1])/cellsize[1]) | ||
| ny = ceiling((bb[4] - offset[2])/cellsize[2]) | ||
| } else { | ||
| n = rep(n, length.out = 2) | ||
| nx = n[1] | ||
| ny = n[2] | ||
| } | ||
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| # corner points: | ||
| if (cellsize_missing) { | ||
| xc = seq(offset[1], bb[3], length.out = nx + 1) | ||
| yc = seq(offset[2], bb[4], length.out = ny + 1) | ||
| } else { | ||
| xc = offset[1] + (0:nx) * cellsize[1] | ||
| yc = offset[2] + (0:ny) * cellsize[2] | ||
| } | ||
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| if (what == "polygons") { | ||
| ret = vector("list", nx * ny) | ||
| square = function(x1, y1, x2, y2) | ||
| st_polygon(list(matrix(c(x1, x2, x2, x1, x1, y1, y1, y2, y2, y1), 5))) | ||
| for (i in 1:nx) | ||
| for (j in 1:ny) | ||
| ret[[(j - 1) * nx + i]] = square(xc[i], yc[j], xc[i+1], yc[j+1]) | ||
| } else if (what == "centers") { | ||
| ret = vector("list", nx * ny) | ||
| cent = function(x1, y1, x2, y2) | ||
| st_point(c( (x1+x2)/2, (y1+y2)/2 )) | ||
| for (i in 1:nx) | ||
| for (j in 1:ny) | ||
| ret[[(j - 1) * nx + i]] = cent(xc[i], yc[j], xc[i+1], yc[j+1]) | ||
| } else if (what == "corners") { | ||
| ret = vector("list", (nx + 1) * (ny + 1)) | ||
| for (i in 1:(nx + 1)) | ||
| for (j in 1:(ny + 1)) | ||
| ret[[(j - 1) * (nx + 1) + i]] = st_point(c(xc[i], yc[j])) | ||
| } else | ||
| stop("unknown value of `what'") | ||
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| if (missing(x)) | ||
| st_sfc(ret, crs = crs) | ||
| else | ||
| st_sfc(ret, crs = st_crs(x)) | ||
| } | ||
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| ### hex grid tesselation that | ||
| ## - covers a bounding box st_bbox(obj) | ||
| ## - contains pt | ||
| ## - has x spacing dx: the shortest distance between x coordinates with identical y coordinate | ||
| ## - selects geometries intersecting with obj | ||
| make_hex_grid = function(obj, pt, dx, what, flat_topped = TRUE) { | ||
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| dy = sqrt(3) * dx / 2 | ||
| bb = st_bbox(obj) | ||
| if (!flat_topped) { # pointy topped -- swap x and y: | ||
| ylim = bb[c("xmin", "xmax")] | ||
| xlim = bb[c("ymin", "ymax")] | ||
| pt = pt[2:1] | ||
| } else { | ||
| xlim = bb[c("xmin", "xmax")] | ||
| ylim = bb[c("ymin", "ymax")] | ||
| } | ||
| offset = c(x = (pt[1] - xlim[1]) %% dx, y = (pt[2] - ylim[1]) %% (2 * dy)) | ||
| x0 = seq(xlim[1] - dx, xlim[2] + 2 * dx, dx) + offset[1] | ||
| y0 = seq(ylim[1] - 2 * dy, ylim[2] + 2 * dy, dy) + offset[2] | ||
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| y <- rep(y0, each = length(x0)) | ||
| x <- rep(c(x0, x0 + dx / 2), length.out = length(y)) | ||
| xy = cbind(x, y) # the coordinates | ||
|
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| # compute the indexes, using double coordinates: | ||
| odd <- seq(1, by = 2, length.out = length(x0)) | ||
| even <- seq(2, by = 2, length.out = length(x0)) | ||
| xi <- rep(c(odd, even), length.out = length(y)) | ||
| yi <- rep(seq_along(y0), each = length(x0)) | ||
| # hexagon centers are columns with x index 3, 6, 9, ... : | ||
| centers = cbind(xi,yi)[xi %in% seq(3, max(xi) - 2, by = 3) & yi > 1 & yi < max(yi),] | ||
|
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| # relative offset in double coordinates, https://www.redblobgames.com/grids/hexagons/ | ||
| nx = length(x0) | ||
| xy_pattern = rbind(c(-2,0), c(-1,-1), c(1,-1), c(2,0), c(1,1), c(-1,1), c(-2,0)) | ||
| i_from_x = function(x) ((x[,1] - 1) %/% 2 + 1) + (x[,2] - 1) * nx | ||
|
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| mk_point = if (flat_topped) | ||
| function(center) st_point(xy[i_from_x(matrix(center, ncol = 2)),]) | ||
| else | ||
| function(center) st_point(xy[i_from_x(matrix(center, ncol = 2)),2:1]) | ||
|
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| mk_pol = if (flat_topped) | ||
| function(center) { | ||
| m = matrix(center, ncol=2, nrow = 7, byrow=TRUE) + xy_pattern | ||
| st_polygon(list(xy[i_from_x(m),])) | ||
| } | ||
| else | ||
| function(center) { | ||
| m = matrix(center, ncol=2, nrow = 7, byrow=TRUE) + xy_pattern | ||
| st_polygon(list(xy[i_from_x(m),2:1])) | ||
| } | ||
|
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| ret = if (what == "points") | ||
| st_sfc(lapply(seq_len(nrow(centers)), function(i) mk_point(centers[i,])), crs = st_crs(bb)) | ||
| else # points: | ||
| st_sfc(lapply(seq_len(nrow(centers)), function(i) mk_pol(centers[i,])), crs = st_crs(bb)) | ||
|
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| if (what == "points") | ||
| ret[obj] | ||
| else | ||
| ret[lengths(st_relate(ret, obj, "2********")) > 0] # part or total overlap | ||
| } |
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