Created
July 2, 2019 10:09
-
-
Save mskyttner/4e72baef580ab1d58fb59440925e077a to your computer and use it in GitHub Desktop.
aisdecode.R
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
library(vikingr) | |
library(dplyr) | |
library(purrr) | |
library(stringr) | |
log <- read_ais_log(vikingr_example("vikingr-visby-2019-ais-2")) | |
log_tail <- | |
log$message %>% | |
str_replace("(.*?,){5}(.*?)", "\\2") | |
log_head <- | |
log$message %>% | |
str_extract("((.*?,){5})") %>% | |
str_remove(",$") %>% | |
readr::read_csv(col_names = letters[1:5]) | |
log_clean <- bind_cols( | |
timestamp = log$timestamp, | |
log_head, | |
message = log_tail | |
) | |
to_payload <- function(message) { | |
message %>% utf8ToInt() - 48 %>% | |
map_dbl(function(x) if_else(x > 40, x - 8, x)) | |
} | |
to_bits <- function(x, n_bits = 8) { | |
x %>% map(~ intToBits(.)[n_bits:1] %>% as.logical) %>% unlist | |
} | |
to_decimal <- function(bits) { | |
# using as.integer means bits should be <= 32 | |
stopifnot(bits <= 32) | |
bits %*% 2^((length(bits) - 1):0) %>% as.integer | |
} | |
decode_bits <- function(bits) { | |
list( | |
msg_type = bits[1:6], | |
repeat_indicator = bits[7:8], | |
mmsi = bits[9:38], | |
nav_stat = bits[39:42], | |
rot = bits[43:50], | |
sog = bits[51:60], | |
pos_acc = bits[61], | |
lon = bits[62:89], | |
lat = bits[90:116], | |
cog = bits[117:128], | |
hdg = bits[118:137] | |
) %>% | |
map_df(to_decimal) %>% | |
mutate_at(vars(lon, lat), ~ . / 600000) | |
} | |
decode_ais <- function(message) { | |
decode_message <- function(x) | |
x %>% to_payload() %>% to_bits() %>% decode_bits() | |
message %>% map_df(decode_message) | |
} | |
# this is the resulting df after decoding the messages | |
df <- bind_cols( | |
log_clean, | |
decode_ais(log_clean$message) | |
) | |
decode_sixbits <- function(payload) { | |
six_bit <- c('@', LETTERS, '[', '\\', ']', | |
'^', '_', ' ', '!', '"', '#', '$', '%', | |
'&', '\'', '(', ')', '*', '+', ',', '-', | |
'.', '/', 0:9, ':', ';', '<', '=', '>', '?') | |
six_bit %>% set_names(c(0:(2^6 - 1))) | |
six_bit[payload] | |
} | |
# we seem not to have any type 5 messages so cannot test this | |
df %>% filter(msg_type == 5) |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment