Using dplyrOracle

geoconvert <- function (x) 
  {
  i <- sign(x)
  x <- abs(x)
  x1 <- x%%10000
  k <- c(1:length(x1))
  k <- k[x1 > 5999 & !is.na(x1)]
  min <- (x/100) - trunc(x/10000) * 100
  return((i * (x + (200/3) * min))/10000)
}

require(dplyr)
#devtools::install_github("tomasgreif/dplyOracle")
require(dplyrOracle)

mar <- src_oracle(dbname='mar')
db_query_fields(mar$con, sql("fiskar.stodvar"))

##  [1] "SYNIS_ID"        "LEIDANGUR"       "DAGS"           
##  [4] "SKIP"            "STOD"            "REITUR"         
##  [7] "SMAREITUR"       "KASTAD_N_BREIDD" "KASTAD_V_LENGD" 
## [10] "HIFT_N_BREIDD"   "HIFT_V_LENGD"    "DYPI_KASTAD"    
## [13] "DYPI_HIFT"       "VEIDARFAERI"     "MOSKVASTAERD"   
## [16] "GRANDARALENGD"   "HEILDARAFLI"     "LONDUNARHOFN"   
## [19] "SKIKI"           "FJARDARREITUR"   "SNT"            
## [22] "SNN"             "SBT"             "SBN"            
## [25] "HNATTSTADA"      "LANDSYNI"        "ATHS"           
## [28] "STADA_STODVAR"   "NET_NR"          "SYNAFLOKKUR"    
## [31] "VEIDISVAEDI"     "HITAMAELIR_ID"   "MAELINGARMENN"  
## [34] "VEIDARFAERI_ID"  "TOG_ATHS"        "MEDFERD_AFLA"

db_query_rows(mar$con, sql('select * from fiskar.stodvar'))

## [1] 302362

st <- mar %>% 
  tbl(sql('SELECT * FROM fiskar.stodvar')) %>%
  collect() %>%
  select(SYNIS_ID, LEIDANGUR, DAGS,
         KASTAD_V_LENGD, KASTAD_N_BREIDD,
         SYNAFLOKKUR) %>%
  filter(lubridate::year(DAGS) == 2015) %>%
  rename(lon=KASTAD_V_LENGD, lat= KASTAD_N_BREIDD) %>%
  mutate(lon= -geoconvert(lon),lat=geoconvert(lat)) 

## [1] "we are here"
## [1] "we are here"

require(ggplot2)
require(ggmap)
gmap <- get_map(location = c(lon = -18, lat = 65),zoom = 5,maptype="satellite")

ggmap(gmap) +
  geom_point(data=st,aes(lon,lat),col="red") +
  labs(x="",y="")