How do I discern Maidenhead Locator from GPS lat long info.

[Darrel Taylor]

Nope, it's 24x24.
And your 10-digit locator is IO93ok03kh.

This version is quite different from the last one.
I've tossed out the stuff that came from the pearl script and did it like the PDF mentioned above.

It has to use the 32-bit floating point routines now. 24-bits just didn't have enough resolution for the sub-squares.
While this version is more efficient, it's also harder to understand, sorry.

; Filename    : Maidenhead_10.pbp
; Compiler    : PICBASIC PRO Compiler
; Target PIC  : 16F1937, but will work with most any chip
; Oscillator  : ANY
; Keywords    : Maidenhead, Locator, GPS, Amateure Radio
; Description : PICBASIC PRO program to convert between
;             : GPS Sexagesimal to Maidenhead coordinate systems
;-------------------------------------------------------------------------------
                       ; Must use the 32-bit Floating Point routines
INCLUDE "FP2032.bas"   ; 32-bit Floating Point for 14-bit cores with RAM at $20

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 25  ' 19200 Baud @ 32MHz, 0.16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

HSEROUT [27,"[2J","Maidenhead Locator",13,10]
HSEROUT ["16F1937, 32-bit Floating Point",13,10,13,10]

MH        VAR BYTE[10]
LonStr    VAR BYTE[12]
LatStr    VAR BYTE[12]
LonDeg    VAR BYTE
LonMin    VAR BYTE
LonMinDec VAR BYTE
LonDir    VAR BYTE
LatDeg    VAR BYTE
LatMin    VAR BYTE
LatMinDec VAR BYTE
LatDir    VAR BYTE
Idx       VAR BYTE
AddChar   VAR BYTE
Divisor   VAR BYTE[4]
AARG_SAVE VAR BYTE[4]

;-------------------------------------------------------------------------------
ASM
MOVE?CF32  macro C, F       ; put a Floating Point Constant in an FP variable
    MOVE?CW  (C & 0xFFFF), F
    MOVE?CW  (C >> 16), F + 2
  endm

MOVE?FF32  macro Fin, Fout  ; Copy an FP var to another FP var
    MOVE?WW  Fin, Fout
    MOVE?WW  Fin + 2, Fout + 2
  endm
ENDASM
;-------------------------------------------------------------------------------

ARRAYWRITE LonStr,["00049.77,W",0]  ;  0° 47.70'  ;<-- enter GPS location here
ARRAYWRITE LatStr,["5325.83,N",0]   ; 53° 26.20'

HSEROUT ["LonStr  = ", STR LonStr,13,10]          ; display manual input
HSEROUT ["LatStr  = ", STR LatStr,13,10]

;----[parse strings as if they came from a GPS]---------------------------------
ARRAYREAD LonStr,[DEC3 LonDeg, DEC2 LonMin, Dec LonMinDec, LonDir]
ARRAYREAD LatStr,[DEC2 LatDeg, DEC2 LatMin, Dec LatMinDec, LatDir]


;----[convert Longitude Sexagesimal to Decimal Degrees]-------------------------
Aint = LonMinDec : GOSUB ItoFA    ; decimal portion of Minutes
Bint = 100 : GOSUB ItoFB          ; divided by 100
GOSUB fpdiv
Bint = LonMin : GOSUB ItoFB       ; add whole portion of Minutes
GOSUB fpadd
Bint = 60 : GOSUB ItoFB           ; divide by 60
GOSUB fpdiv
Bint = LonDeg : GOSUB ItoFB       ; add degrees
GOSUB fpadd
IF LonDir = "W" THEN              ; if west of Prime Meridian
    @ MOVE?FF32 AARGB2, BARGB2    ; copy Float AARG to BARG
    Aint = 0    : GOSUB ItoFA     ; subtract from 0 to negate
    GOSUB fpsub
ENDIF

Bint = 180  : GOSUB ItoFB         ; add 180
GOSUB fpadd

;----[Have Longitude in AARG as Float]------------------------------------------
FOR Idx = 0 TO 8 STEP 2
    SELECT CASE Idx
      CASE 0 : AddChar = "A"
               @ MOVE?CF32 0x83200000, _Divisor   ; 20
      CASE 2 : AddChar = "0"
               @ MOVE?CF32 0x80000000, _Divisor   ; 2
      CASE 4 : AddChar = "a"
               @ MOVE?CF32 0x7B2AAAAB, _Divisor   ; 0.0833333
      CASE 6 : AddChar = "0"
               @ MOVE?CF32 0x78088889, _Divisor   ; 0.00833333
      CASE 8 : AddChar = "a"
               @ MOVE?CF32 0x73360B61, _Divisor   ; 0.000347222
    END SELECT
    GOSUB MH_Digit
NEXT Idx

;----[convert Latitude Sexagesimal to Decimal Degrees]--------------------------
Aint = LatMinDec : GOSUB ItoFA    ; decimal portion of Minutes
Bint = 100 : GOSUB ItoFB          ; divided by 100
GOSUB fpdiv
Bint = LatMin : GOSUB ItoFB       ; add whole portion of Minutes
GOSUB fpadd
Bint = 60 : GOSUB ItoFB           ; divide by 60
GOSUB fpdiv
Bint = LatDeg : GOSUB ItoFB       ; add degrees
GOSUB fpadd
IF LatDir = "S" THEN              ; if south of equator
    @ MOVE?FF32 AARGB2, BARGB2    ; copy Float AARG to BARG
    Aint = 0    : GOSUB ItoFA     ; subtract from 0 to negate
    GOSUB fpsub
ENDIF

Bint = 90  : GOSUB ItoFB          ; add 90
GOSUB fpadd

;----[Have Latitude  in AARG as Float]------------------------------------------
FOR Idx = 1 TO 9 STEP 2
    SELECT CASE Idx
      CASE 1 : AddChar = "A"
               @ MOVE?CF32 0x82200000, _Divisor   ; 10
      CASE 3 : AddChar = "0"
               @ MOVE?CF32 0x7F000000, _Divisor   ; 1
      CASE 5 : AddChar = "a"
               @ MOVE?CF32 0x7A2AAAAB, _Divisor   ; 0.0416666
      CASE 7 : AddChar = "0"
               @ MOVE?CF32 0x770882F1, _Divisor   ; 0.00416666
      CASE 9 : AddChar = "a"
               @ MOVE?CF32 0x723603EC, _Divisor   ; 0.000173583
    END SELECT
    GOSUB MH_Digit
NEXT Idx
;----[Maidenhead conversion complete]-------------------------------------------

HSEROUT ["LOC ",STR MH\10,13,10,13,10] ; show final result

Main:                             ; blink an LED when done
    HIGH PORTA.0
    PAUSE 500
    LOW PORTA.0
    PAUSE 500
GOTO Main

;----[Calculate one digit of the Maidenhead Locator]----------------------------
MH_Digit:
    @ MOVE?FF32 _Divisor, BARGB2      ; put divisor in BARG
    GOSUB fpdiv                       ; do the divide
    @ MOVE?FF32 AARGB2, _AARG_SAVE    ; save AARG for modulus

    GOSUB FtoIA                       ; get integer
    MH(Idx) = Aint + AddChar          ; The Character
    Bint = Aint                       ; copy integer result to BARG
    GOSUB ItoFB                       ; convert it to float
    @ MOVE?FF32 _AARG_SAVE, AARGB2    ; restore previous AARG
    GOSUB fpsub                       ; subtract integer

    @ MOVE?FF32 _Divisor, BARGB2      ; multiply times original divisor
    GOSUB fpmul                       ; AARG now contains the remainder
RETURN

The output of the program looks like this ...

Maidenhead Locator
16F1937, 32-bit Floating Point

LonStr  = 00049.77,W
LatStr  = 5325.83,N
LOC IO93ok03kh

BTW: Those are really small squares (in red).