[OZAPRS] Packet disassembly help needed

[Merv Joyce]

Andrew,

The followingg routine is in Delphi (pascal) ... It should translate
pretty easily.
"TS" is an object for the "station" that owns this data. Parameter "S"
is everything
After the timestamp "HHMMSSz" .  String "S" is 1-based array in pascal
(not 0-based).
Its not perfect, but it’s a start ..........

------------------------------------------------------------------------
---------------------------------   procedure GetCompPosit(s: string;
var N,E: LongInt);
   var
      nr,er: real;
      b: integer;

      function power(base,ex: real): real;
      begin
         if (Abs(Base)<0.000001)
         then begin
                 Power := 0;
                 Exit;
              end;
         power := exp(ex*ln(abs(base)));
      end;

   begin
      N := -1; E := -1;
      if not (length(s)=13) then exit;

      Try
      TS.Symbol_Table := s[ 1];;
      TS.Symbol_Index := s[10];

      (* extract latitude *)

      lat := 90.0 -
             (((ord(s[2])-33)*91.0*91.0*91.0) +
              ((ord(s[3])-33)*91.0*91.0)    +
              ((ord(s[4])-33)*91.0)       +
              ((ord(s[5])-33)))/380926.0;

      (* extract longitude *)

      long := - 180.0 +
             (((ord(s[6])-33)*91.0*91.0*91.0) +
              ((ord(s[7])-33)*91.0*91.0)    +
              ((ord(s[8])-33)*91.0)       +
              ((ord(s[9])-33)))/190463.0;

      (* now calculate northing and easting *)

      Calc_LL2NE(lat,long,map,nr,er);
      N := round(nr);
      E := round(er);

      if not (s[11]=' ')
      then begin
              (* course/speed *)
              b := ord(s[11])-33;
              if b in [0..89]
              then begin
                      TS.course := 4 * b;
                      TS.speed  := 1.852 *
(power(1.08,(ord(S[12])-33))-1);
                   end
              else begin
                      TS.course := 0.0;
                      TS.speed  := 0.0;
                   end;

              (* radio range *)
              if s[11]='{'
              then begin
                      (* range := 2 * power(1.08,(ord(S[12])-33)); *)
                   end;

               (* and we ignore the decoding of the last char (c[13]) -
the T-byte *)
           end;

      TS.posit_when := w;
      TS.posit_path := TS.path;
      TS.posit_msg  := TS.msg;

      Except
         on E: Exception do Application.MessageBox(PChar(E.Message),
                                                   'Exception Trap
during "APRS_Server:GetCompPosit"',
                                                   MB_OKCANCEL);
      end;
   end;
------------------------------------------------------------------------
---------------------------------


Merv Joyce (VK4ZE)


-----Original Message-----
From: ozaprs-bounces at marconi.ics.mq.edu.au
[mailto:ozaprs-bounces at marconi.ics.mq.edu.au] On Behalf Of vk4tec
Sent: Sunday, 21 November 2004 11:25
To: ozaprs
Subject: [OZAPRS] Packet disassembly help needed


Hi,

Does anyone have some perl code I can use to uncompress

VK4YBN>APRS,VK4RAI-3*,VK4GME-3*,WIDE:
@210039z/\G;Xt{68>+GzBob VK4YBN, 2004 Summer Challenge {UIV23N}

@ (Compressed with timestamp)
210039z (HHMMSSz)
/ (sym table)
\G;X (YYYY)
t{68 (XXXX)
> (symbol)
+Gz (csT)
Bob VK4YBN, 2004 Summer Challenge {UIV23N} (comment)

I need to be able to return the ascii value of a number as well.

and do powers of 91 calculations

Cheers Andy VK4TEC

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