polar-anim.R

## Function that creates a polar plot
polar.plot <- function(df, i){
  # Add bridges for polar coordinates
  years <- unique(df$year)[1:i]
  df2 <- filter(df, year %in% years)
  bridges <- df2[df2$month == 'Jan',]
  bridges$year <- bridges$year - 1
  if(nrow(bridges) == 0){
    bridges <- data.frame(site = df2$site[1], year = min(df2$year), month = NA, anom = NA)
  } else {
    bridges$month <- NA
  }
  blanks <- data.frame(site = df2$site[1], expand.grid(year = min(df2$year)-1, month = month.abb), anom = NA)
  # Polar plot
  pp <- ggplot(data = rbind(blanks, df2, bridges), aes(x = month, y = anom, group = year)) +
    # Circular black background
    geom_rect(colour = "black", fill = "black", aes(xmin = "Jan", xmax = NA,
                  ymin = min(df$anom, na.rm = T), ymax = max(df$anom, na.rm = T))) +
                  # ymin = min(df$anom, na.rm = T), ymax = 3)) +
    # Anomaly threshold labels
    geom_hline(aes(yintercept = 1.0), colour = "red") +
    geom_label(aes(x = "Jan", y = 1.0, label = "1.0°C"),
               colour = "red", fill = "black", size = 3) +
    geom_hline(aes(yintercept = 2.0), colour = "red") +
    geom_label(aes(x = "Jan", y = 2.0, label = "2.0°C"),
               colour = "red", fill = "black", size = 3) +
    geom_hline(aes(yintercept = 3.0), colour = "red") +
    geom_label(aes(x = "Jan", y = 3.0, label = "3.0°C"),
               colour = "red", fill = "black", size = 3) +
    geom_hline(aes(yintercept = 4.0), colour = "red") +
    geom_label(aes(x = "Jan", y = 4.0, label = "4.0°C"),
               colour = "red", fill = "black", size = 3) +
    # Temperature spiral
    geom_path(aes(colour = anom), show.legend = F) +
    geom_point(data = df2[i,], aes(colour = anom), show.legend = F) +
    # Scale corrections
    scale_colour_viridis(limits = c(min(df$anom, na.rm = T), max(df$anom, na.rm = T))) +
    scale_x_discrete(expand = c(0,0), breaks = month.abb) +
    scale_y_continuous(expand = c(0,0),
                       limits = c(min(df$anom, na.rm = T), max(df$anom, na.rm = T))) +
    # Year label
    geom_text(aes(x = "Jan", y = min(df$anom, na.rm = T), label = max(df2$year, na.rm = T)),
              colour = "ivory", size = 8) +
    # Additional tweaks
    ggtitle(paste0(df$site[1]," temperature change (",min(df$year),"-",max(df$year),")")) +
    coord_polar() +
    theme(panel.background = element_rect(fill = "grey20"),
          plot.background = element_rect(fill = "grey20"),
          panel.grid.major = element_blank(),
          panel.grid.minor = element_blank(),
          # axis.text.x = element_text(colour = "ivory"),
          axis.text.x = element_text(colour = "ivory", angle =
            (360/(2*pi)*rev(seq(pi/12, 2*pi-pi/12, len = 12)))+15,
            size = 12),
          axis.text.y = element_blank(),
          axis.title = element_blank(),
          axis.ticks = element_blank(),
          axis.ticks.length = unit(0, "cm"),
          plot.title = element_text(hjust = 0.5, colour = "ivory", size = 15))
  print(pp)
}

## Create animation of polar plots
animate.polar.plot <- function(df) {
  lapply(seq(1,length(unique(df$year))), function(i) {
    polar.plot(df = df, i = i)
  })
}