geo3x3.prg

OPTION STRICT

COMMON DEF GEO3X3_ENCODE(LAT,LNG,LV%)
 IF LV%<1 THEN RETURN ""
 
 DIM RES$="E"
 
 IF LNG<0.0 THEN
  RES$="W"
  INC LNG,180.0
 ENDIF
 
 INC LAT,90.0
 
 DIM I%
 DIM UNIT=180.0
 
 FOR I%=1 TO LV%-1
  UNIT=UNIT/3.0
  
  DIM X%=FLOOR(LNG/UNIT)
  DIM Y%=FLOOR(LAT/UNIT)
  DIM N%=X%+Y%*3+1
  
  RES$=RES$+STR$(N%)
  
  DEC LNG,X%*UNIT
  DEC LAT,Y%*UNIT
 NEXT
 
 RETURN RES$
END

COMMON DEF GEO3X3_DECODE CODE$,RES[]
 DIM CLEN%=LEN(CODE$)
 
 IF CLEN%==0 THEN RETURN
 
 DIM BEGIN%,FLG%=#FALSE
 DIM C$=CODE$[0]
 
 IF C$=="-" || C$=="W" THEN
  FLG%=#TRUE
  BEGIN%=1
 ELSEIF C$=="+" || C$=="E" THEN
  BEGIN%=1
 ENDIF
 
 DIM LAT,LNG,UNIT=180.0
 DIM I%,LV%=1
 
 FOR I%=BEGIN% TO CLEN%-1
  DIM N%=VAL(CODE$[I%])
  
  IF N%<=0 THEN BREAK
  
  UNIT=UNIT/3.0
  DEC N%
  INC LNG,(N% MOD 3)*UNIT
  INC LAT,FLOOR(N%/3)*UNIT
  INC LV%
 NEXT
 
 INC LAT,UNIT/2
 INC LNG,UNIT/2
 DEC LAT,90.0
 
 IF FLG% THEN DEC LNG,180.0
 
 RES[0]=LAT:RES[1]=LNG
 RES[2]=LV%:RES[3]=UNIT
END