Parsing take #3

I want to make more structured messages so I parse the lists using a function I call compose/1 for this I again use Erlangs superior pattern matching.

So for GPGSA the compose looks like:

compose(["GPGSA",A,B,C1,C2,C3,C4,C5,C6,C7,C8,C9,C10,C11,C12,D,E,F]) ->
    {gsa,
     {auto,list_to_atom(A)},
     {fix,list_to_integer(B)},
     {satellites,satellites([C1,C2,C3,C4,C5,C6,C7,C8,C9,C10,C11,C12],[])},
     {pdop,list_to_float(D)},
     {horizdi,list_to_float(E)},
     {vertdi,list_to_float(F)}};

This will only match the lists with "GPGSA" sentences (my GPS device only submits the sentences GPGSA,GPGGA,GPRMC,GPGSV).

The structured data I use are simple tuples, where I use Erlang atoms as identifiers for the fields, as you can see I also translate the integer data into integers (and for other messages to float values). A helper function is used so I do not repeat my self to much:

satellites([[] | _], Satellites) ->
   Satellites;
satellites([A | Rest], Satellites) ->
   satellites(Rest, [list_to_integer(A) | Satellites]).

The rest of compose for parsing the remaining sentences looks like:

compose(["GPGGA",A,B1,B2,C1,C2,D,E,F,G1,G2,H1,H2,I,J]) ->
   {gga,
    {fixtime,A},
    {lattitude,[list_to_float(B1)/100,list_to_atom(B2)]},
    {longitude,[list_to_float(C1)/100,list_to_atom(C2)]},
    {quality,list_to_integer(D)},
    {numberofsatellites,list_to_integer(E)},
    {horizdi,list_to_float(F)},
    {altitude,[list_to_float(G1),list_to_atom(G2)]},
    {geoidheight,[list_to_float(H1),list_to_atom(H2)]},
    {timesincedgps,list_to_float(I)},
    {dgpsstation,J}};

compose(["GPRMC",A,B,C1,C2,D1,D2,E,F,G,H1,H2]) ->
   {rmc,
    {fixtime,A},
    {status,list_to_atom(B)},
    {lattitude,[list_to_float(C1)/100,list_to_atom(C2)]},
    {longitude,[list_to_float(D1)/100,list_to_atom(D2)]},
    {speed,list_to_float(E)},
    {trackangle,list_to_float(F)},
    {date,G},
    {magneticvariation,[H1,H2]}};

compose(["GPGSV",A,B,C | SateliteData ]) ->
   {gsv,
    {numberofsentences,list_to_integer(A)},
    {number,list_to_integer(B)},
    {numberofsatellites,list_to_integer(C)},
    satellitedata(SateliteData, [])}.

I divide the longitude/lattitudes by 100 as I wish that they closely match the expected format for Google maps.

The GPGSV sentences are variable length so I use a helper function for parsing those:

satellitedata([D,E,F,G | SateliteData ], Satellites) ->
   satellitedata(SateliteData, 
                 [{sattelite,list_to_integer(D)},
                  {elevation,list_to_integer(E)},
                  {azimuth,list_to_integer(F)},
                  {snr,list_to_integer(G)} | Satellites]);
satellitedata([], Satellites) ->
   Satellites.

My final loop/1 looks like this:

loop(Port) ->
   receive
       {Port, {data, Data}} ->
           case Data of
               <<"$", Rest/binary>> ->
                   Tokens = tokenize (Rest),
                   Record = compose(Tokens),
                   io:format("~p~n", [Record]);
               _ ->
                   sl:setopt(Port, mode, line),
                   sl:update(Port)
           end,
           loop(Port);
       stop  ->
           exit(normal);
       {'EXIT', Port, Reason} ->
           exit({port_terminated, Reason})
   end.

The resulting messages are reported in the shell like:

{rmc,{fixtime,"214612.620"},
    {status,'A'},
    {lattitude,[29.9792,'N']},
    {longitude,[31.1343,'E']},
    {speed,9.00000e-2},
    {trackangle,81.9100},
    {date,"291107"},
    {magneticvariation,[[],[]]}}
{gga,{fixtime,"214613.620"},
    {lattitude,[29.9792,'N']},
    {longitude,[31.1343,'E']},
    {quality,1},
    {numberofsatellites,4},
    {horizdi,4.00000},
    {altitude,[146.2000,'M']},
    {geoidheight,[0.0000,'M']},
    {timesincedgps,0.00000e+0},
    {dgpsstation,"0000"}}
{gsa,{auto,'A'},
    {fix,3},
    {satellites,[2,23,20,31]},
    {pdop,7.30000},
    {horizdi,4.00000},
    {vertdi,6.00000}}
{rmc,{fixtime,"214613.620"},
    {status,'A'},
    {lattitude,[56.2778,'N']},
    {longitude,[10.2091,'E']},
    {speed,0.100000},
    {trackangle,100.610},
    {date,"291107"},
    {magneticvariation,[[],[]]}}

Note I still need to parse the dates and times into some nice representations.
I will next time make an additional process which will receive these messages and report only the position data in a format compatible with Google maps