Revised Figure11.txt

100 :
110 REMark Set ShowTrack% to 0 for orbits, 1 for track
120 ShowTrack%= 0
130 REMark For orbits: set Blobs% to 1 for blobs, 0 for lines
140 Blobs%= 1
150 :
160 CLOSE
170 REMark Serial Port: 6 for PC, 1 for Laptop
180 SerPort%= 6
190 maxid= 30: REMark highest permitted satellite id no.
200 :
210 IF ShowTrack% >0 THEN
220   Minlon=0: Minlat=0: Maxlon=0: Maxlat=0
230   REMark PRINT Minlon,Minlat,Maxlon,Maxlon
240   REMark For displaying track must set min and max
250   REMark   lat and lon or call a procedure to do so ...
260   ChiCityMap
270   REMark PfdMap
280   :
290   REMark See Jan Jones page 39, 40
300   IF (1+ Minlon+ Minlat+ Maxlon+ Maxlat)= 1 THEN
310     CLS
320     PRINT \\\"   *** Map limits not set ***": STOP
330   END IF
340 END IF
350 :
360 COLOUR_PAL
370 REMark For orbit display:
380 REMark Colours used for spot showing first observed
390 REMark position and use of satellite
400 seentint%= 194: usdtint%= 96
410 :
420 REMark ***********************************
430 sim= 1: REMark Set to 0 for receiver input
440 REMark                1 for file input
450 REMark Set dtof to 1 to save raw data to win1_sats_data
460 dtof= 0
470 REMark No point in saving already saved data!
480 IF sim <> 0 THEN dtof = 0
490 REMark ***********************************
500 :
510 CLS#0: CLS
520 CSIZE 0,0
530 :
540 REMark Set up the Serial Port if needed
550 IF sim THEN
560   REMark Serial Port simulated by data file
570   cs%= FOP_IN("win1_gps_sats_dat")
580 :
590 ELSE
600   REMark For real time data from receiver
610   REMark SerPort% set to 6 or 1 at start of program
620   BAUD SerPort%,4800
630   SerPort$= SerPort%
640   cs%= FOPEN("srx"&SerPort$&"IA")
650 END IF
660 :
670 REMark Window to display raw data
680 dd%= FOPEN ("con")
690 WINDOW #dd%,550,75,0,525
700 BORDER #dd%,1,9,1
710 PAPER #dd%,36: INK #dd%,0: CLS #dd%
720 :
730 REMark Window to display error and other messages
740 REMark in particular, corrupted data
750 de%= FOPEN ("con")
760 WINDOW #de%,400,75,400,45
770 BORDER #de%,1,9,1
780 PAPER #de%,39: INK #de%,0: CLS #de%: REMark paper was 36
790 :
800 REMark Delay in seconds between readings
810 REMark to avoid enormous sats_data file
820 INPUT "Delay in seconds",delay
830 :
840 REMark Window for main display of orbits or track
850 asprat= .8: REMark aspect ratio: width/height
860 size = 3.5: REMark for early fiddling with windows
870 dc%= FOPEN ("con")
880 Mctr= COS(RAD((Minlat+Maxlat)/2))
890 High= 100*size
900 Wide= 137*size*asprat
910 WINDOW #dc%,Wide,High,0,525-High
920 BORDER #dc%,1,9,1
930 INK #dc%,0
940 PAPER #dc%,37: CLS #dc%
950 :
960 REMark 
====================================================
970 REMark Set up for track display
980 IF ShowTrack% <>0 THEN
990   difflon= Maxlon- Minlon
1000   difflat= Maxlat- Minlat
1010   SCALE #dc%,difflat,Minlon*asprat*Mctr, Minlat
1020   :
1030   REMark Lat and Lon grid
1040   LatLonGrid
1050   :
1060   REMark window to show instantaneous track and speed
1070   dt%= FOPEN ("scr")
1080   Topdc%= 525-High+3
1090   WINDOW #dt%,137/4*size*asprat,100/4*size,285,Topdc%:
1100   BORDER #dt%,1,9,1
1110   SCALE #dt%,200,-100*asprat,-100
1120   PAPER #dt%,37: CLS #dt%:
1130  ELSE
1140   REMark For orbit display
1150   SCALE #dc%,2.2,-1.1*asprat,-1.1
1160   REMark Set up alternative for orbits
1170   SatSky
1180 END IF
1190 REMark =================================================
1200 :
1210 REMark Open a file to collect the data for simulation
1220 IF dtof <> 0 THEN
1230   fc%= FOP_NEW(win1_sats_data)
1240 END IF
1250 :
1260 REMark ::::::::::::::::::::::::::::::::::::::::::::::::::
1270 REMark This was originally the only display, put DEF PROC
1280 REMark round it to allow alternative track display
1290 REMark Window #dc% already defined as same size for both
1300 DEFine PROCedure SatSky
1310   REMark Sky disk
1320   FILL#dc%,1
1330   INK#dc%,29
1340   ELLIPSE#dc%,0,0,1,1*asprat,0
1350   FILL#dc%,0
1360   :
1370   REMark Draw polar plot grid lines
1380   INK#dc%,12
1390   radials : REMark draw the bearings
1400   REMark now draw the elevations
1410   FOR i = 1 TO 3
1420    ELLIPSE#dc%,0,0,i/3,1*asprat,0
1430   END FOR
1440   LINE#dc%,-1.02*asprat,0 TO 1.02*asprat,0
1450   LINE#dc%,0,-1.02 TO 0,1.02
1460   :
1470   REMark Mark points of compass
1480   INK#dc%,9
1490   CURSOR#dc%,1.03*asprat,0,0,-4
1500   PRINT#dc%,"E"
1510   CURSOR#dc%,-1.03*asprat,0,-6,-4
1520   PRINT#dc%,"W"
1530   CURSOR#dc%,0,1.04,-3,-8
1540   PRINT#dc%,"N"
1550   CURSOR#dc%,0,-1.03,-3,2
1560   PRINT#dc%,"S"
1570   :
1580   REMark Mark azimuth scale
1590   FOR i= 30 TO 330 STEP 30
1600     IF (i MOD 90) = 0 THEN NEXT i
1610     j= i+90
1620     CURSOR#dc%,1.03*COS(j*PI/180)*asprat,1.03*SIN
(j*PI/180),-6,-5
1630     PRINT#dc%,360-i
1640   END FOR i
1650   :
1660   REMark mark elevation scale
1670   FOR i= 0 TO 3
1680     CURSOR#dc%,0,i/3,-6,-5
1690     PRINT#dc%,90-30*i
1700   END FOR i
1710 END DEFine SatSky
1720 :
1730 
REMark ::::::::::::::::::::::::::::::::::::::::::::::::::::
1740 :
1750 REMark Display set up, now get ready for GPS data
1760 :
1770 REMark Array to store raw data lines from receiver
1780 DIM rawdata$(5,128)
1790 REMark Array to store satellite data ..
1800 REMark with:  IdNo, Bearing, Elevation, Usage
1810 REMark where: Usage is 0 for not used, 1 for used.
1820 DIM satsvis(11,3) : REMark Allow for 12 satellites in 
view
1830 :
1840 DIM satsusd(11)   : REMark List of Ids of  satellites 
used.
1850 :
1860 REMark I use copies of the raw data ...
1870 DIM satlist$(6,128):REMark Satellite data from $GPSGV 
input
1880 REMark Allow for 7 $GPSV lines (OTT -- never more than 
2!)
1890 :
1900 DIM rmcdata$(128) : REMark Lat, Long, Time
1910 :
1920 REMark Posns for orbits plotted as lines
1930 REMark to draw a blob for first point, then a line
1940 REMark Store: Old x,y; New x,y: 5th item, 0= new orbit ..
1950 REMark .. so draw a blob, 1= orbit started so draw line
1960 DIM posns(maxid,5): REMark need enough for each satellite
1970 REMark set all to zero for a start
1980 FOR i%= 0 TO maxid-1
1990   FOR j%= 0 TO 4
2000     posns(i%,j%)= 0
2010   END FOR j%
2020 END FOR i%
2030 :
2040 CLS
2050 REMark For plotting track, need a POINT to start
2060 REMark then continue with lines.
2070 REMark Don't bother not defining this if orbits
2080 FirstPt%=0
2090 :
2100 lines=0:      REMark A count of input lines
2110 GoodLines=0: REMark Another count of input lines
2120 CLS #dd%: REMark I needed this for raw data display
2130 :
2140 REMark 
=====================================================
2150 REMark Setting up complete, now for ...
2160 REMark ... data reading and display
2170 :
2180 REMark Repeat loop for continous display
2190 REMark delay at end
2200 REMark Each run through loop deals with a single set
2210 REMark of data sentences, five in my case, starting
2220 REMark with a $GPGGA. Sent each second, but read
2230 REMark at a rate determined by missing some with the 
delay
2240 REMark Test for end in gpsdata$ function
2250 :
2260 REPeat orbits
2270   AT #dd%,0,0: AT 0,0: REMark To keep the display tidy
2280   REMark I read all the sentences at one go so that I
2290   REMark don't end up with some from a later second's 
lot.
2300   rawdata$(0)= gpsdata$("$GPGGA"): REMark Wait for a 
first
2310   rawdata$(1)= gpsdata$("$GPGSA"): REMark ... read the 
rest
2320   rawdata$(2)= gpsdata$("$GPGSV")
2330   rawdata$(3)= gpsdata$("$GPGSV")
2340   rawdata$(4)= gpsdata$("$GPRMC")
2350   lines=  lines+5: REMark lines, GoodLines  bit messy ...
2360   REMark ... intended it to help look at corrupted data
2370   REMark Check lines for not corrupted data
2380   FOR i= 0 TO 4
2390     REMark Go through data to look for corrupted lines.
2400     REMark This became a long winded process, so that is
2410     REMark why I read all the sentences in one go.
2420     REMark Ignoring all the set of data, if there is one
2430     REMark corrupted item ,is a bit OTT, but safe.
2440     :
2450     REMark Sometimes get lines much longer than spec. ..
2460     REMark .. 'Long' lines seem to be a normal line 
but ..
2470     REMark .. no <CR><LF> and followed by more, ..
2480     REMark  .. badly formed, data, so ignore them:
2490     ChkFld%= '*' INSTR rawdata$(i)
2500     IF LEN(rawdata$(i)) > ChkFld%+ 3 THEN NEXT orbits
2510     :
2520     IF dtof <> 0 THEN
2530       PRINT #fc%,rawdata$(i): REMark Save in file if 
needed
2540     END IF
2550     :
2560     REMark Ckeck 'Checksum' field
2570     Check%= CheckSum(rawdata$(i))
2580     IF Check% <> 0 THEN
2590      NEXT orbits
2600     END IF
2610     GoodLines= GoodLines+1
2620     DisLine dd%,GoodLines&" "&rawdata$(i),0
2630   END FOR i
2640 :
2650 REMark Get ready forlist of satellites used
2660 REMark from $GPGSA data line
2670 gpsAdata$ = rawdata$(1): REMark cautiously use copies
2680 :
2690 REMark Get ready for list of satellite data
2700 REMark First $GPGSV line gives no of $GPSV lines
2710 satlist$(1) = rawdata$(2)
2720 REMark Extract number of $GPGSV lines
2730 novrecs% = satlist$(1,8)
2740 :
2750 REMark Get rest of $GPGSV lines
2760 REMark FOR j= 2 to novrecs%
2770 REMark  satlist$(j)= gpsdata$("GPGSV")
2780 REMark END FOR
2790 REMark Had trouble with that so .. assumed always two ...
2800 satlist$(2)= rawdata$ (3)
2810 :
2820 REMark Get RMC data
2830 REMark Too late now, but should use a copy of raw data!
2840 gpsrmc$= gpsdata$ ( "$GPRMC")
2850 :
2860 REMark Start at first $GPGSV line
2870 t$= satlist$(1): REMark To leave full data for later
2880 f$= field$(chop$(t$,3))
2890 REMark IF NumChk(f$)<>0 THEN NEXT orbits
2900 novsats%= f$
2910 :
2920 REMark Now have all the data needed for display
2930 :
2940 REMark Extract satellites used into satsusd array
2950 REMark from $GPGGA line
2960 v$= chop$(gpsAdata$,2)
2970 i= 0: REMark Count for sused REPeat loop
2980 PRINT \" Sats used   : ";
2990 :
3000 REMark Extract time and validity
3010 UTC$= GPSTime$(rawdata$(4))
3020 Inv%= 0: REMark to record invalid time and data
3030 IF gpsrmc$(18)= "V": Inv%=1
3040 :
3050 REPeat sused
3060   v$= chop$(gpsAdata$,1)
3070   REMark Mark end of list with -1
3080   IF v$(1)="," THEN satsusd(i)= -1: EXIT sused
3090   f$= field$(v$)
3100   IF LEN(f$) =0 THEN NEXT orbits
3110   satsusd(i)=f$
3120   IF satsusd(i)<10 THEN PRINT "0";
3130   PRINT satsusd(i);" ";
3140   i= i+1
3150 END REPeat sused
3160 :
3170 REMark Spaces at end of 'used' line for shorter overwrite
3180 PRINT "      "
3190 :
3200 PRINT " Sats in view: ";
3210 :
3220 REMark Extract data from $GPGSV lines
3230 v$= satlist$(1)
3240 v$= chop$(v$, 2)
3250 FOR i= 1 TO novsats%
3260   v$= chop$(v$, 2)
3270   id$= field$( v$ ): REMark Satellite Identifier
3280   IF LEN(id$) =0 THEN NEXT orbits
3290   id%= id$
3300   IF id%<10 THEN PRINT "0";
3310   PRINT id%!;
3320   v$= chop$ ( v$, 1 ): REMark Satellite elevation
3330   el$= field$( v$ )
3340   IF LEN(el$) =0 THEN NEXT orbits
3350   el%= el$
3360   v$= chop$ ( v$, 1 ): REMark Satellite azimuth
3370   az$= field$( v$ )
3380   IF LEN(el$) =0 THEN NEXT orbits
3390   IF NumChk(az$)<>0 THEN NEXT orbits
3400   az%= az$
3410   j= 0: tint%= seentint%
3420   REPeat chkid
3430     IF satsusd(j)= -1 THEN EXIT chkid
3440     IF satsusd(j)= id% THEN
3450       tint%= usdtint%
3460     END IF
3470     j= j+1
3480   END REPeat chkid
3490   :
3500   IF ShowTrack% =0 THEN
3510     REMark At last can plot satellite in position
3520     REMark Plot omly valid data
3530     IF Inv%=0 THEN : spot el%, az%, id%, tint%
3540   END IF
3550   REMark Change data line after 4 sats
3560   IF (i MOD 4)= 0 THEN v$= chop$(satlist$(2),2)
3570 END FOR i
3580 :
3590 REMark Spaces at end of 'ids' line for shorter overwrite
3600 PRINT "      "
3610 :
3620 REMark Print validity
3630 PRINT \"   ";
3640 IF Inv%=1: PRINT "Inv";: ELSE PRINT "V";
3650 PRINT "alid Position  "
3660 REMark Spaces to overwrite longer 'Invalid' message
3670 :
3680 REMark Extract Lat and Long
3690 REMark Chopped gpsrmc$ also used by Track code
3700 REMark so use a variable to synchronise
3710 rmchop%= 3
3720 gpsrmc$= chop$(gpsrmc$, rmchop%)
3730 CSIZE 3,1
3740 AT 3,0
3750 REMark Latitude
3760 PRINT "  ";gpsrmc$( 1 TO 2); CHR$(186);
3770 PRINT " ";gpsrmc$(3 TO 10);"'"!gpsrmc$(12);
3780 LatDeg$= gpsrmc$( 1 TO 2)
3790 LatMin$= gpsrmc$(3 TO 10)
3800 Lat= DecDeg(LatDeg$,LatMin$)
3810 IF gpsrmc$(12) =="S" THEN Lat= -Lat
3820 REMark Validity
3830 PRINT "  "; Validity$
3840 REMark Longitude
3850 PRINT " ";gpsrmc$(14 TO 16); CHR$(186);
3860 PRINT " ";gpsrmc$(17 TO 24);"'"! gpsrmc$(26)
3870 LonDeg$= gpsrmc$(14 TO 16)
3880 LonMin$= gpsrmc$(17 TO 24)
3890 Lon= DecDeg(LonDeg$,LonMin$)
3900 IF gpsrmc$(26)== "W" THEN Lon= -Lon
3910 :
3920 REMark Display UTC, extracted way back
3930 AT 6,2
3940 PRINT UTC$;
3950 :
3960 REMark Extract Track data,
3970 REMark    gprsmc$ already chopped for Lat, Long
3980 AT 8,2
3990 trak$= gpsrmc$: trak$= chop$(trak$, 7-rmchop%)
4000 speed$= trak$(1 TO 5)
4010 IF NumChk(speed$)<>0 THEN CSIZE 0,0: NEXT orbits
4020 Speed= speed$* 1.150779: REMark Convert Knots to m.p.h.
4030 PRINT "Track"!trak$(7 TO 11);CHR$(186): REMark Bearing
4040 PRINT_USING "     at ##.# m.p.h", Speed
4050 Brg= trak$(7 TO 11)
4060 :
4070 CSIZE 0,0
4080 :
4090 IF ShowTrack% THEN
4100   REMark Show track as a line: colour shows speed
4110   INK #dc%,Spink%(Speed)
4120   IF FirstPt%==0 THEN
4130     POINT #dc%, Lon*asprat*Mctr, Lat
4140     FirstPt%= 1
4150    ELSE
4160     LINE #dc% TO Lon*asprat*Mctr, Lat
4170   END IF
4180 :
4190   REMark Show Speed and bearing as a line, ..
4200   REMark .. length and colour for speed, ..
4210   REMark .. bearing as direction of line.
4220   CLS #dt%: INK #dt%,Spink%(Speed)
4230   POINT #dt%,0,0
4240   PENDOWN #dt%
4250   TURNTO #dt%,90-Brg: MOVE #dt%,Speed
4260   PENUP #dt%
4270 END IF
4280 :
4290 REMark Pause to slow down rate of refreshment of display
4300 PAUSE 50*delay
4310 :
4320 REMark End of repeat loop for continous display
4330 END REPeat orbits
4340 CLOSE #cs%: IF dtof <>0 THEN CLOSE #dc%
4350 STOP
4360 :
4370 REMark End of Main Program 
=================================
4380 :
4390 DEFine PROCedure radials
4400   REMark Draws the celestial meridians at 30 deg 
intervals
4410   REMark as a series of dots to avoid too dark a line
4420   LOCal i,j,interval
4430   interval = 2E-2
4440   FOR i = 0 TO 350 STEP 10
4450     FOR j= 2 TO 100
4460       REMark uses j*interval as a radial distance ..
4470       REMark .. which must be converted to x,y for plot
4480       IF j*interval > 1 THEN EXIT j
4490       POINT#dc%,j*interval*COS(i*PI/180)
*asprat,j*interval*SIN(i*PI/180)
4500     END FOR j
4510   END FOR i
4520 END DEFine
4530 :
4540 DEFine PROCedure spot(elvn,azm,id,tint)
4550 REMark Draw a blob in tint at elvn,azm and show id
4560 REMark For a polar plot need to convert to x,y coords
4570 REMark Code for line plot added later
4580 LOCal x,y,srad
4590 REMark ignore data if id outside possible range ..
4600 REMark .. it has happened, usually during start up of RX
4610 IF id > maxid THEN RETurn
4620 srad= (90-elvn)/90: REMark zero to one on plot
4630 x= srad*SIN(azm*PI/180)*asprat
4640 y= srad*COS(azm*PI/180)
4650 REMark Copy previous posn as 'old'
4660 posns(id,0)= posns(id,2)
4670 posns(id,1)= posns(id,3)
4680 REMark Save new posn for 'old' next time
4690 posns(id,2)= x
4700 posns(id,3)= y
4710 INK #dc%,tint: STRIP #dc%,tint
4720 REMark Draw sat as blob if first time plotted ...
4730 IF posns(id,4)< 1 OR Blobs% =1 THEN
4740   posns(id,4)= 1: REMark Remember as blobbed
4750   REMark draw a blob
4760   FILL#dc%,1
4770    ELLIPSE#dc%,x,y,6E-2,asprat,0
4780   FILL#dc%,0
4790   REMark Show sat id in contrasing ink
4800   IF tint= seentint% THEN INK #dc%,0: ELSE INK #dc%,7
4810   CURSOR#dc%,x,y,-6,-5
4820   IF id<10 THEN PRINT#dc%,0;: REMark Add leading zero?
4830   PRINT#dc%,id: REMark At last, print sat id
4840 ELSE
4850 REMark ... otherwise draw a line
4860   INK #dc%,tint: LINE #dc%,posns(id,0),posns(id,1) 
TO                       posns(id,2),posns(id,3): INK #dc%,0
4870 END IF
4880 END DEFine
4890 :
4900 DEFine FuNction gpsdata$( id$ )
4910   REMark Waits for and reads a sentence of data starting
4920   REMark with the string id$ (not sat id this time)
4930   REMark Give up if there's no data to serial port
4940   FOR i= 1 TO 50
4950     IF EOF(#cs%) THEN
4960       AT 20,3: PRINT "Lines: ";lines!;
4970                PRINT " Good lines: ";GoodLines
4980                INPUT "   Press <enter> to finish: ";t$
4990       CLS: CLS#0: CLS#2: CLOSE: STOP
5000     END IF
5010     INPUT #cs%,t$
5020     REMark More checks for dodgy data
5030     IF LEN(t$) = 0 THEN NEXT i
5040     IF t$(1) <> "$" THEN NEXT i
5050     IF t$(1 TO 6) = id$ THEN RETurn t$:
5060   END FOR
5070   IF i > 10 THEN PRINT " No GPS data": STOP
5080 END DEFine
5090 :
5100 DEFine FuNction field$(str$)
5110   REMark Extracts the first field from the NMEA message 
data
5120   REMark after it has been chopped to the start of the
5130   REMark field, with comma separated fields, so making
5140   REMark no assumption about the field length.
5150   LOCal k%
5160   REMark last field terminated by * at start of checksum
5170   REMark so need to check for ',' -- if none then '*'
5180   k%= "," INSTR str$
5190   IF k% =0 THEN k%= "*" INSTR str$
5200   RETurn str$ ( TO (k%-1))
5210   REMark NOTE errors such as empy string must be
5220   REMark dealt with on return from call
5230 END DEFine
5240 :
5250 DEFine FuNction NumChk(a$)
5260 REMark Check if a$ contains a decimal number, fixed point
5270 REMark Return: 0= ok; 1= empty; 2= >1 d.ps; 3= non-
numeric
5280  LOCal i%,a%,NoDecPts%: NoDecPts%= 0
5290  REMark NoDecPts% holds the nunber of dec pts found
5300  IF LEN(a$) = 0 THEN RETurn 1
5310  FOR i% = 1 TO LEN(a$)
5320    a%= CODE (a$(i%))
5330    REMark 48 and 57 are codes for '0' and '9'
5340    REMark .. I just like < more than <=
5350    IF a% > 47 AND a < 58 THEN
5360      NEXT i%
5370     ELSE
5380      REMark Check for dec pt
5390      IF a%=46 THEN
5400        NoDecPts%= NoDecPts%+1: REMark Allow one dec. pt.
5410        IF NoDecPts%> 1 THEN RETurn 2: ELSE NEXT i%
5420      END IF
5430     RETurn 3
5440    END IF
5450  END FOR i%
5460  RETurn 0
5470 END DEFine
5480 :
5490 DEFine FuNction chop$(str$, skip)
5500   REMark Chops off skip fields from the start of str$
5510   REMark Haven't had to chop as far as the '*' yet
5520   LOCal i,j
5530   IF ( skip < 1 ) THEN RETurn str$
5540   FOR i= 1 TO skip
5550     j= "," INSTR str$
5560     str$ = str$ ( j+1 TO )
5570   END FOR
5580   RETurn str$
5590 END DEFine
5600 :
5610 DEFine PROCedure DisLine(c%,t$,l%)
5620   REMark Diplays line padded to l% chars with spaces ..
5630   REMark .. in channel #c%, the spaces are needed
5640   REMark when short lines follow long
5650   REMark Had no success with CLS so far
5660   PRINT #c%;t$;
5670   tl%= LEN(t$)
5680   IF tl%< l% THEN
5690     PRINT #c%;FILL$(" ",l%-tl%)
5700    ELSE PRINT #c%
5710   END IF
5720 END DEFine
5730 :
5740 DEFine FuNction GPSTime$(t$)
5750  REMark Extracts time from t$ -- copy of RMC input
5760  REMark Should have used chop$ etc, but by this time the
5770  REMark data format seemed stable enough and CBB took 
over.
5780   t$= chop$(t$,1): REMark Remove '$GPRMC'
5790   RETurn '@ '&t$(1 TO 2)&':'&t$(3 TO 4)&':'&t$(5 TO 6)&' 
UTC'
5800 END DEFine GPSTime$
5810 :
5820 DEFine FuNction CheckSum(a$)
5830 LOCal i,aa$,ChkSum,ChkCode$
5840 IF LEN(a$)=0 THEN RETurn -2
5850 FOR i= 1 TO 256: REMark Allow for sentence ..
5860   REMark        .. not terminated properly, i.e. no '*'
5870   aa$= a$(i)
5880   SELect ON CODE(aa$)
5890       REMark set ChkSum to zeros at start of sentence
5900     = CODE('$'): ChkSum= 0
5910     = CODE('*'):
5920       ChkCode$= a$((i+1) TO (i+2))
5930       EXIT i
5940     = REMAINDER :
5950       REMark ^^ is 'bit-wise exclusive OR' Jan Jones p 40
5960       ChkSum= CODE(aa$) ^^ ChkSum
5970   END SELect
5980 END FOR i
5990 REMark Checksum in data is two hex chars (8 bits)
6000 IF HEX$(ChkSum,8) = ChkCode$ THEN
6010   RETurn 0: REMark Good result
6020  ELSE
6030   REMark Bad result
6040    PRINT #de%,a$;" ChkSum: ";HEX$(ChkSum,8);" Check 
code: ";ChkCode$
6050    RETurn -1
6060 END IF
6070 END DEFine
6080 :
6090 REMark Follow a series of definitons of charts for tracks
6100 REMark Maxlon necessary for lat, lon grid
6110 DEFine PROCedure ChiCityMap
6120   Minlat= 50+49/60
6130   Maxlat= 50+51/60
6140   Minlon= -47/60
6150   Maxlon= -43/60
6160 END DEFine
6170 :
6180 DEFine PROCedure PfdMap
6190   Minlat= 50.7667
6200   Maxlat= 51.05
6210   Minlon= -1-3/60
6220   Maxlon= -.6
6230 END DEFine
6240 :
6250 DEFine FuNction DecDeg(D$,M$)
6260  IF LEN(D$)==0 OR LEN(M$)==0 THEN RETurn 361
6270  IF ',' INSTR(D$&M$) THEN RETurn 362
6280  RETurn D$+(M$/60)
6290 END DEFine
6300 :
6310 DEFine FuNction Spink%(S)
6320   REMark Returns a colour according to the Speed S
6330   SELect ON S
6340    ON S=0  TO  9.999: RETurn 0   : REMark Black
6350    ON S=10 TO 19.999: RETurn 59  : REMark Brown
6360    ON S=20 TO 29.999: RETurn 2   : REMark Red
6370    ON S=30 TO 39.999: RETurn 236 : REMark Yellow
6380    ON S=40 TO 49.999: RETurn 22  : REMark Orange
6390    ON S=50 TO 59.999: RETurn 3   : REMark Green
6400    ON S=60 TO 69.999: RETurn 25  : REMark Blue
6410    ON S=70 TO 79.999: RETurn 26  : REMark Violet
6420    REMark Shocking pink for over 80m.p.h.
6430    ON S= REMAINDER : RETurn 112
6440   END SELect
6450 END DEFine
6460 :
6470 DEFine PROCedure LatLonGrid
6480 REMark For track, prints a grid of lats and longs ..
6490 REMark .. each at one minute of arc intervals
6500 REMark parameters set in main program
6510 REMark No need for precise match to window as SB
6520 REMark just doesn't draw outside it
6530 LOCal Glat, Glon, Gld, Glm
6540 INK #dc%,13: REMark nice pale grey
6550 :
6560 REMark Start with latitudes
6570 Gl= Minlat
6580 REMark Need to convert to decimal degrees
6590 Gl= INT(Gl)+(INT((Gl-INT(Gl))*60))/60
6600 Gminl= Minlon*asprat*Mctr: Gmaxl= Maxlon*asprat*Mctr
6610 REPeat LatLines
6620    IF Minlat<=Gl AND Maxlat > Gl THEN
6630      LINE #dc%, Gminl,Gl TO Gmaxl,Gl
6640    END IF
6650    Gl= Gl+1/60
6660    IF Gl> Maxlat THEN EXIT LatLines
6670 END REPeat
6680 :
6690 REMark next meridians
6700 Gl= Minlon
6710 Gl= INT(Gl)+(INT((Gl-INT(Gl))*60))/60
6720 Gminl= Minlon: Gmaxl= Maxlon
6730 REPeat LonLines
6740    IF Minlon <= Gl AND Maxlon > Gl THEN
6750      Gp= Gl*asprat*Mctr
6760      LINE #dc%, Gp,Minlat TO Gp,Maxlat
6770    END IF
6780    Gl= Gl+1/60
6790    IF Gl> Maxlon THEN EXIT LonLines
6800 END REPeat
6810 END DEFine
6820 :
6830 REMark My programs always have this procedure at the end
6840 DEFine PROCedure backup
6850   SAVE dos1_GPSTalk_QLMags_Figure11.txt
6860 END DEFine