Make Google Traffic Raster

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(
  location,
  height,
  width,
  zoom,
  google_key,
  traffic_color_dist_thresh = 4.6,
  traffic_color_dist_metric = "CIEDE2000",
  webshot_zoom = 1,
  webshot_delay = NULL,
  print_progress = TRUE
)

Arguments

location

Vector of latitude and longitude

height

Height (in pixels; pixel length depends on zoom)

width

Width (in pixels; pixel length depends on zoom)

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.

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. Larger height/widths require longer delay times. If NULL, the following delay time (in seconds) is used: delay = max(height,width)/200.

print_progress

Whether to print function progress (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) {
r <- gt_make_raster(location   = c(40.712778, -74.006111),
                    height     = 1000,
                    width      = 1000,
                    zoom       = 16,
                    google_key = "GOOGLE-KEY-HERE")
}