Make Google Traffic Raster Based on Polygon — gt_make_raster_from

Make a raster of Google traffic data, where each pixel has one of four values indicating traffic volume (no traffic, light, moderate, and heavy).

Usage

gt_make_raster_from_polygon(
  polygon,
  zoom,
  google_key,
  height_width_max = 2000,
  height = NULL,
  width = NULL,
  traffic_color_dist_thresh = 4.6,
  traffic_color_dist_metric = "CIEDE2000",
  webshot_zoom = 1,
  webshot_delay = NULL,
  reduce_hw = 10,
  return_list_of_rasters = FALSE,
  mask_to_polygon = TRUE,
  print_progress = TRUE
)

Arguments

polygon: Polygon (sf object or SpatialPolygonsDataframe) in WGS84 CRS
zoom: Zoom level; integer from 5 to 20. For more information about how zoom levels correspond to pixel size, see here and here.
google_key: Google API key, where the Maps JavaScript API is enabled. To create a Google API key, follow these instructions.
height_width_max: Maximum pixel height and width to check using for each API query (pixel length depends on zoom). If the same number of API queries can be made with a smaller height/width, the function will use a smaller height/width. If height and width are specified, that height and width will be used and height_width_max will be ignored. (Default: 2000)
height: Height, in pixels, for each API query (pixel length depends on zoom). Enter a height to manually specify the height; otherwise, a height of height_width_max or smaller will be used.
width: Pixel, in pixels, for each API query (pixel length depends on zoom). Enter a width to manually specify the width; otherwise, a width of height_width_max or smaller will be used.
traffic_color_dist_thresh: Google traffic relies on four main base colors: #63D668 for no traffic, #FF974D for medium traffic, #F23C32 for high traffic, and #811F1F for heavy traffic. Slight variations of these colors can also represent traffic. By default, the base colors and all colors within a 4.6 color distance of each base color are used to define traffic; by default, the CIEDE2000 metric is used to determine color distance. A value of 2.3 is one threshold used to define a "just noticeable distance" (JND) between colors (by default, 2 X JND is used). This parameter changes the color distance from the base colors used to define colors as traffic. For more information, see here.
traffic_color_dist_metric: See above; this parameter changes the metric used to calculate distances between colors. By default, CIEDE2000 is used; CIE76 and CIE94 can also be used. For more information, see here.
webshot_zoom: How many pixels should be created relative to height and width values. If height and width are set to 100 and webshot_zoom is set to 2, the resulting raster will have dimensions of about 200x200 (default: 1).
webshot_delay: How long to wait for Google traffic layer to render (in seconds). Larger height/widths require longer delay times. If NULL, the following delay time (in seconds) is used: delay = max(height,width)/200.
reduce_hw: Number of pixels to reduce height/width by. Doing so creates some overlap between grids to ensure there is not blank space between tiles. (Default: 10).
return_list_of_rasters: Whether to return a list of raster tiles instead of mosaicing together. (Default: FALSE).
mask_to_polygon: Whether to mask raster to polygon. (Default: TRUE).
print_progress: Show progress for which grid / API query has been processed. (Default: TRUE).

Value

Returns a georeferenced raster. Raster pixels can contain the following values: 1 = no traffic; 2 = medium traffic; 3 = high traffic; 4 = heavy traffic.

References

Markus Hilpert, Jenni A. Shearston, Jemaleddin Cole, Steven N. Chillrud, and Micaela E. Martinez. Acquisition and analysis of crowd-sourced traffic data. CoRR, abs/2105.12235, 2021.

Pavel Pokorny. Determining traffic levels in cities using google maps. In 2017 Fourth International Conference on Mathematics and Computers in Sciences and in Industry (MCSI), pages 144–147, 2017.

Examples

if (FALSE) {
## Grab polygon of Manhattan
us_sp <- raster::getData('GADM', country='USA', level=2)
ny_sp <- us_sp[us_sp$NAME_2 %in% "New York",]

## Make raster
r <- gt_make_raster_from_polygon(polygon    = ny_sp,
                                 height     = 2000,
                                 width      = 2000,
                                 zoom       = 16,
                                 google_key = "GOOGLE-KEY-HERE")
}