library(ggmap)
library(rgdal)
library(ggplot2)

#####################################


## build data frame with triangulation data

t1 <- c(534325, 4858925, 338, 0955)
t2 <- c(534383, 4859261, 290, 1010)
t3 <- c(534386, 4859011, 301, 1015)

df <- as.data.frame(rbind(t1, t2, t3))
colnames(df) <- c("Easting", "Northing", "Azimuth", "Time")
df$Time <- as.character(df$Time)

## plot coordinates with triangulation

ggplot(df, aes(x=Easting, y=Northing, label=Time)) +
  geom_point() +
  geom_text(nudge_x = 50) +
  geom_spoke(aes(angle = Azimuth, radius = -500)) +
  theme_bw()

## convert utms to lat long

utmcoor <- SpatialPoints(cbind(df$Easting,df$Northing),
proj4string=CRS("+proj=utm +zone=12"))
lonlatcoor <- as.data.frame(spTransform(utmcoor,CRS("+proj=longlat")))
colnames(lonlatcoor) <- c("lon", "lat")

df$lon <- lonlatcoor$lon
df$lat <- lonlatcoor$lat

## plot on base map

zoom <- 15

meanlon <- mean(df$lon)
meanlat <- mean(df$lat)

basemap <- get_googlemap(center=c(lon=meanlon, lat=meanlat), zoom=zoom,
maptype="hybrid")

ggmap(basemap) +
  geom_point(aes(x=lon, y=lat), colour="red", size=2, data=df) +
  geom_spoke(aes(x=lon, y=lat, angle = Azimuth), data=df, radius=-200) +
  theme_void()

Warning message:
Removed 3 rows containing missing values (geom_segment).