Libraries

library(data.table)
library(ggplot2)
library(lubridate)
library(gganimate)

Read and Preprocess Data

Using data from KDD CUP of Fresh Air.

bj_aq <- rbindlist(lapply(Sys.glob("../data/bj_*_renamed_aq.csv", dirmark = FALSE), fread))
bj_station <- fread("../data/Beijing_AirQuality_Stations.csv")
# Dedup
bj_aq <- bj_aq[!duplicated(bj_aq, from_last=T)]
# Parse time
bj_aq[, time:=with_tz(ymd_hms(bj_aq[, time], tz="UTC"), tz="Asia/Shanghai")]
# Filling Gaps in Time
full_keys <- expand.grid(
    time=seq(ymd_hms("2017-01-01 16:00:00"), 
             ymd_hms("2018-03-30 16:00:00"), 
             by="1 hour"),
    station_id=unique(bj_aq[,station_id])
)
bj_aq_full <- merge(bj_aq, full_keys, by=c("time", "station_id"), all.y=T)
bj_aq_full <- merge(bj_aq_full, bj_station, by="station_id")

Single Snaphot

(Missing data points are colored white.)

# Single snapshot
p <- ggplot(bj_aq_full[time==ymd_hms("2017-01-02 00:00:00")], 
       aes(x=Longitude, y=Latitude, fill=PM25_Concentration)) +
    geom_point(size=3, pch=21, color="grey50") + scale_fill_gradient(
        low = "#FFFF99", high = "#990000",
        na.value = "grey50", guide = "colourbar") 
p + theme_minimal() + 
    theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())

Animation Over A Short Period of Time

(Missing data points are colored white.)

p <- ggplot(bj_aq_full[time<ymd_hms("2017-01-10 00:00:00")], 
            aes(x=Longitude, y=Latitude, fill=pmin(500, PM25_Concentration),
                frame=time, cumulative=FALSE)) +
    geom_point(size=8, pch=21, color="grey50") + 
    scale_fill_gradient(low = "#FFFF99", high = "#990000",
        na.value = "white", guide = "colourbar") 
p <- p + theme_minimal() + labs(fill="PM25") +
    theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())
animation <- gganimate(p, "animation_tmp.gif", interval = 0.5, ani.width = 1280, ani.height = 720)
# gganimate(p, interval = 0.5, ani.width = 1280,
#   ani.height = 720, filename="pm25_0101_0110.mp4", other.opts = "-pix_fmt yuv420p")
Animation

Animation