Package 'slippymath'

bbox_tile_extent

Description

Convert a bounding box from latitude and longitude to tile numbers

Usage

bbox_tile_extent(bbox, zoom)

Arguments

bbox	a bbox object created by 'sf::st_bbox', or a vector with names 'xmin', 'xmax', 'ymin', 'ymax'
zoom	zoom level to calculate the tile grid on.

Details

This function creates an analog of a bounding box but in tile numbers. It returns the min and max x and y tile numbers for a tile grid that would fit the bounding box for a given zoom level.

Value

a list of 'x_min', 'y_min', 'x_max', 'y_max'

Examples

tibrogargan<- c(xmin = 152.938485, ymin = -26.93345, xmax = 152.956467, 
               ymax = -26.921463)
bbox_tile_extent(tibrogargan, zoom = 15)

---

bbox_tile_query

Description

Bounding box tile query

Usage

bbox_tile_query(bbox, zoom_levels = 2:18)

Arguments

bbox	a bbox object created by 'sf::st_bbox', or a vector with names 'xmin', 'xmax', 'ymin', 'ymax'
zoom_levels	a numeric vector of zoom levels to calculate tile usage for.

Details

Determines how many tiles the bounding box would occupy for a range of zooms. Useful for working out what is a reasonable zoom to work at. Each tile is a separate request from the server.

Tiles are typically 256x256 pixels and are tens of Kb in size, you can get some sense of the data from the query also.

Value

a data frame containing tile usage information for the bounding box at each zoom level.

Examples

tibrogargan<- c(xmin = 152.938485, ymin = -26.93345, xmax = 152.956467, 
               ymax = -26.921463)

bbox_tile_query(tibrogargan)

---

bbox_to_tile_grid

Description

Bounding box to tile grid

Usage

bbox_to_tile_grid(bbox, zoom = NULL, max_tiles = NULL)

Arguments

bbox	the bounding box to fit onto a grid of tiles. Must be either a 'bbox' object created with sf::st_bbox or a vector of length 4 with names: 'xmin', 'xmax', 'ymin', 'ymax'.
zoom	Optional. The desired zoom level.
max_tiles	Optional. The maximum number of tiles the grid may occupy.

Details

Calculate a slippy map tile grid that will fit a supplied bounding box.

The grid is returned as part of a tile_grid object that contains a data.frame of x,y tile numbers and zoom level.

The tile grid can be calculated for a given zoom level or for the deepest zoom that ensures the number of tiles is less than or equal to 'max_tiles'.

If 'zoom' and 'max_tiles' are supplied together, then the max is still enforced and the function will fail if more tiles are required for the given zoom.

Value

a 'tile_grid' object containing 'tiles' and 'zoom'

Examples

tibrogargan<- c(xmin = 152.938485, ymin = -26.93345, xmax = 152.956467, 
               ymax = -26.921463)

## Get a grid of the minimum number of tiles for a given zoom.
bbox_to_tile_grid(tibrogargan, zoom = 15)

## get a grid of at most 12 tiles, choosing the most detailed zoom possible.
bbox_to_tile_grid(tibrogargan, max_tiles = 12)

---

compose_tile_grid

Description

Compose a list of images using tile_grid data.

Usage

compose_tile_grid(tile_grid, images)

Arguments

tile_grid	a tile_grid object, likely returned from 'bbox_to_tile_grid'
images	a list of character strings defining paths to images. Matched to tiles in tile_grid based on list position.

Details

Given a tile_grid object and a list of images, compose the images into a single spatially referenced RasterBrick object.

The list of images is assumed to be in corresponding order to the tiles in the tile_grid object.

The returned object uses the Web Mercator projection, EPSG:3857, which is the native crs of the tiles.

Value

a spatially referenced raster.

---

Transform between spherical Mercator and longitude/latitude

Description

Transform between spherical Mercator and longitude/latitude

Usage

lonlat_to_merc(ll)

merc_to_lonlat(xy)

Arguments

ll	matrix of longitude / latitude
xy	matrix of x / y Mercator

Value

matrix of coordinates transformed forward or inverse

Examples

uluru_lonlat <- matrix(c(131.0325162,
                         -25.3448562),
                       nrow = 1)

lonlat_to_merc(uluru_lonlat)

uluru_merc <- matrix(c(14586472.958481,
                       -2918162.223463),
                     nrow = 1)

merc_to_lonlat(uluru_merc)

---

lonlat_to_tilenum

Description

Convert longitude and latitude to slippy tile numbers

Usage

lonlat_to_tilenum(lon_deg, lat_deg, zoom)

Arguments

lon_deg	degrees longitude for point
lat_deg	degrees latitude for point
zoom	zoom level for tile calculation. Increasing zoom increases the number of tiles.

Details

Returns the Open Street Map slippy map tile numbers (x, y) the supplied latitude and longitude fall on, for a given zoom level.

The point specified by lon_deg' and 'lat_deg' is assumed to be in ESPG:4326 coordinate reference system.

Value

a list containing 'x' and 'y' - the tile numbers.

Examples

lonlat_to_tilenum(
 lon = 13.37771496361961,
 lat = 52.51628011262304,
 zoom = 17
)

---

merc_truncate

Description

Truncate coordinate to Mercator extent.

Usage

merc_truncate(xy)

Arguments

xy	a matrix of Mercator XY points.

Details

If a point in m lies outside the Mercator extent, this function can be used to truncate it to the boundary of the extent.

Value

a matrix of XY points.

Examples

stray <- matrix(c(20037509,
                   -2918162.223463),
                 nrow = 1)

merc_truncate(stray)

---

raster_to_png

Description

Write a raster to PNG

Usage

raster_to_png(tile_raster, file_path)

Arguments

tile_raster	the raster to write to PNG
file_path	the path to write the raster

Details

This function is a convenience wrapper for writing rasters in PNG format.

Value

nothing.

---

tile_bbox

Description

Calculate the bounding box for a tile in latitude and longitude

Usage

tile_bbox(x, y, zoom)

Arguments

x	slippy map tile x number
y	slippy map tile y number
zoom	zoom level for tile

Details

Given a slippy maps tile specified by 'x', 'y', and 'zoom', return the an 'sf' bounding box object for the tile with units in metres using the EPSG:3857 coordinate reference system (Web Mercator).

Value

an sf bbox object.

Examples

## return an sf style bbox object in with epsg and proj4string
tile_bbox(x = 30304, y = 18929, zoom = 15)

---

tile_grid_bboxes

Description

Get tile grid bounding boxes

Usage

tile_grid_bboxes(tile_grid)

Arguments

tile_grid

a tile_grid object, likely returned from 'bbox_to_tile_grid'

Details

Given an tile_grid object like that returned from 'bbox_to_tile_grid', return a list of sf style bounding box objects, one for each tile in the grid, in the same order as tiles in 'tile_grid$tiles'.

The bounding box units are metres in the EPSG:3857 coordinate reference system (Web Mercator).

Value

a list of sf bounding box objects in the corresponding order to the tiles in 'tile_grid'

Examples

tibrogargan<- c(xmin = 152.938485, ymin = -26.93345, xmax = 152.956467, 
               ymax = -26.921463)

tibrogargan_grid <- bbox_to_tile_grid(tibrogargan, zoom = 15)

tile_grid_bboxes(tibrogargan_grid)

---

tilenum_to_lonlat

Description

Convert slippy map tiles numbers to latitude and longitude

Usage

tilenum_to_lonlat(x, y, zoom)

Arguments

x	slippy map tile number in x domain (left to right)
y	slippy map tile number in y domain (top to bottom)
zoom	the zoom level for the calculation. Increasing zoom increases the number of tiles.

Details

Returns the latitude and longitude of the top left corner of a slippy map tile specified by 'x', 'y' for a given zoom level.

Value

a list containing 'lat' and 'lon' - latitude and longitude.

Examples

tilenum_to_lonlat(
 x = 70406,
 y = 42987,
 zoom = 17
)

---

within_mercator_extent

Description

Are points in meters within Mercator extent?

Usage

within_merc_extent(xy)

Arguments

xy	a matrix of Mercator xy coordinates.

Details

When doing maths with Mercator coordinates in m, you can end up outside the Mercator extent with an undefined coordinate. This function returns true if all xy lie within the Mercator extent.

Value

TRUE or FALSE

Examples

stray <- matrix(c(20037509,
                   -2918162.223463),
                 nrow = 1)

within_merc_extent(stray)

---